AD7172-2BRUZ-RL - ANALOG DEVICES

Low Power, 24-Bit, 31.25 kSPS, Sigma-Delta

ADC with True Rail-to-Rail Buffers

Data Sheet

AD7172-2

Rev. A Document Feedback

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FEATURES

Fast and flexible output rate: 1.25 SPS to 31.25 kSPS

Channel scan data rate of 6.21 kSPS/channel (161 µs settling)

Performance specifications

17.2 noise free bits at 31.25 kSPS

24 noise free bits at 5 SPS

INL: ±2 ppm of FSR

85 dB rejection of 50 Hz and 60 Hz with 50 ms settling

User configurable input channels

2 fully differential channels or 4 single-ended channels

Crosspoint multiplexer

On-chip 2.5 V reference (±2 ppm/°C drift)

True rail-to-rail analog and reference input buffers

Internal or external clock

Power supply

AVDD1 = 3.0 V to 5.5 V, AVDD2 = IOVDD = 2 V to 5.5 V

Split supply with AVDD1 and AVSS at ±2.5 V or ±1.65 V

ADC current: 1.5 mA

Temperature range: −40°C to +105°C

3- or 4-wire serial digital interface (Schmitt trigger on SCLK)

Serial port interface (SPI), QSPI-, MICROWIRE-, and DSP-

compatible

APPLICATIONS

Process control: PLC/DCS modules

Temperature and pressure measurement

Medical and scientific multichannel instrumentation

Chromatography

GENERAL DESCRIPTION

The AD7172-2 is an intelligent, low noise, low power, multiplexed,

Σ-Δ analog-to-digital converter (ADC) with 2- or 4-channel

(fully differential/single-ended) inputs for low bandwidth

signals. The AD7172-2 has a maximum channel scan rate of

6.21 kSPS (161 µs) for fully settled data. The output data rates

range from 1.25 SPS to 31.25 kSPS.

The AD7172-2 integrates key analog and digital signal condition-

ing blocks to allow users to configure an individual setup for each

analog input channel in use via the SPI. Integrated true rail-to-rail

buffers on the analog inputs and external reference inputs provide

easy to drive high impedance inputs. The precision 2.5 V low drift

(2 ppm/°C) band gap internal reference (with an output reference

buffer) adds embedded functionality to reduce the external

component count.

The digital filter allows simultaneous 50 Hz and 60 Hz rejection

at a 27.27 SPS output data rate. The user can switch between

different filter options according to the demands of each channel in

the application, with further digital processing functions such as

offset and gain calibration registers, which are also configurable on

a per channel basis. General-purpose inputs/outputs (GPIOs)

control external multiplexers synchronous to the ADC conversion

timing.

The specified operating temperature range is −40°C to +105°C.

The AD7172-2 is in a 24-lead TSSOP package.

Note that, throughout this data sheet, the dual function pin

names are referenced by the relevant function only.

FUNCTIONAL BLOCK DIAGRAM

AVSS GPIO0 GPIO1 XTAL1 XTAL2/CLKIO DGND

REF–

AVDD1

AVSS

REF+ REFOUT

AIN0

AIN1

AIN2

AIN3

AIN4

Σ-Δ ADC

1.8V

LDO

INT

REF

AVDD1 AVDD2 REGCAPA

1.8V

LDO

IOVDD REGCAPD

GPIO AND

MUX

I/O CONTROL

SERIAL

INTERFACE

AND CONTROL

TEMPERATURE

SENSOR

DIGITAL

FILTER

AD7172-2

BUFFERED

PRECISION

REFERENCE

XTAL AND INTERNAL

CLOCK OSCILLATOR

CIRCUITRY

SCLK

DIN

DOUT/RDY

SYNC/ERROR

CROSSPOINT

MULTIPLEXER

AVDD

AVSS

RAIL-TO-RAIL

ANALOG INPUT

BUFFERS

RAIL-TO-RAIL

REFERENCE

INPUT BUFFERS

12672-001

Figure 1.

AD7172-2 Data Sheet

Rev. A | Page 2 of 60

TABLE OF CONTENTS

Features .............................................................................................. 1

Applications ....................................................................................... 1

General Description ......................................................................... 1

Functional Block Diagram .............................................................. 1

Revision History ............................................................................... 3

Specifications ..................................................................................... 4

Timing Characteristics ................................................................ 7

Timing Diagrams .......................................................................... 8

Absolute Maximum Ratings ............................................................ 9

Thermal Resistance ...................................................................... 9

ESD Caution .................................................................................. 9

Pin Configuration and Function Descriptions ........................... 10

Typical Performance Characteristics ........................................... 12

Noise Performance and Resolution .............................................. 19

Getting Started ................................................................................ 20

Power Supplies ............................................................................ 21

Digital Communication ............................................................. 21

AD7172-2 Reset .......................................................................... 22

Configuration Overview ........................................................... 22

Circuit Description ......................................................................... 27

Buffered Analog Input ............................................................... 27

Crosspoint Multiplexer .............................................................. 27

AD7172-2 Reference .................................................................. 28

Buffered Reference Input ........................................................... 29

Clock Source ............................................................................... 29

Digital Filters ................................................................................... 30

Sinc5 + Sinc1 Filter ..................................................................... 30

Sinc3 Filter ................................................................................... 30

Single Cycle Settling ................................................................... 31

Enhanced 50 Hz and 60 Hz Rejection Filters ......................... 34

Operating Modes ............................................................................ 37

Continuous Conversion Mode ................................................. 37

Continuous Read Mode ............................................................. 38

Single Conversion Mode ........................................................... 39

Standby and Power-Down Modes ............................................ 40

Calibration ................................................................................... 40

Digital Interface .............................................................................. 41

Checksum Protection................................................................. 41

CRC Calculation ......................................................................... 42

Integrated Functions ...................................................................... 44

General-Purpose Input/Output................................................ 44

External Multiplexer Control ................................................... 44

Delay ............................................................................................ 44

16-Bit/24-Bit Conversions......................................................... 44

DOUT_RESET ........................................................................... 44

Synchronization .......................................................................... 44

Error Flags ................................................................................... 45

DATA_STAT ............................................................................... 45

IOSTRENGTH ........................................................................... 46

Internal Temperature Sensor .................................................... 46

Grounding and Layout .................................................................. 47

Communications Register ......................................................... 49

Status Register ............................................................................. 50

ADC Mode Register ................................................................... 51

Interface Mode Register ............................................................ 52

Data Register ............................................................................... 53

GPIO Configuration Register ................................................... 54

ID Register................................................................................... 55

Channel Register 0 ..................................................................... 55

Channel Register 1 to Channel Register 3 .............................. 56

Setup Configuration Register 0 ................................................ 57

Setup Configuration Register 1 to Setup Configuration

Filter Configuration Register 0 ................................................. 58

Filter Configuration Register 1 to Filter Configuration

Offset Register 0 ......................................................................... 59

Offset Register 1 to Offset Register 3 ....................................... 59

Gain Register 0............................................................................ 59

Gain Register 1 to Gain Register 3 ........................................... 59

Outline Dimensions ....................................................................... 60

Ordering Guide .......................................................................... 60

Data Sheet AD7172-2

Rev. A | Page 3 of 60

REVISION HISTORY

3/16—Rev. 0 to Rev. A

Changes to Figure 1........................................................................... 1

Change to Figure 17, Figure 18, and Figure 19 ........................... 14

Changes to Figure 20 and Figure 21 ............................................. 14

Changes to Figure 40 and Figure 41 ............................................. 18

Changes to Power Supplies Section .............................................. 20

Changes to Buffered Analog Input Section ................................. 27

Changes to Figure 65 Caption, Figure 66 Caption, and

Figure 67 Caption ............................................................................ 35

Changes to Figure 69 Caption ....................................................... 36

Changes to Delay Section ............................................................... 44

10/14—Revision 0: Initial Version

AD7172-2 Data Sheet

Rev. A | Page 4 of 60

SPECIFICATIONS

AVDD1 = 3.0 V to 5.5 V, AVDD2 = IOVDD = 2 V to 5.5 V, AVSS = DGND = 0 V, REF+ = 2.5 V, REF− = AVSS,

MCLK = internal master clock = 2 MHz, TA = TMIN to TMAX (−40°C to +105°C), unless otherwise noted.

Table 1.

Parameter Test Conditions/Comments Min Typ Max Unit

ADC SPEED AND PERFORMANCE

Output Data Rate (ODR) 1.25 31,250 SPS

No Missing Codes1 Excluding sinc3 filter ≥ 15 kSPS 24 Bits

Resolution See Table 6 and Table 7

Noise See Table 6 and Table 7

ACCURACY

Integral Nonlinearity (INL) ±2 ±5 ppm of FSR

Offset Error2 Internal short ±40 µV

Offset Drift Internal short ±65 nV/°C

Gain Error2 AVDD1 = 5 V ±5 ±45 ppm of FSR

Gain Drift ±0.2 ±0.5 ppm/°C

REJECTION

Power Supply Rejection AVDD1, AVDD2, VIN = 1 V 98 dB

Common-Mode Rejection VIN = 0.1 V

At DC

At 50 Hz, 60 Hz1 20 Hz output data rate (postfilter), 50 Hz ±

1 Hz and 60 Hz ± 1 Hz

120 dB

Normal Mode Rejection1 50 Hz ± 1 Hz and 60 Hz ± 1 Hz

Internal clock, 20 SPS ODR (postfilter) 71 90 dB

External clock, 20 SPS ODR (postfilter) 85 90 dB

ANALOG INPUTS

Differential Input Range VREF = (REF+) − (REF−) ±VREF V

Absolute Voltage Limits1

Input Buffers Disabled AVSS − 0.05 AVDD1 + 0.05 V

Input Buffers Enabled AVSS AVDD1 V

Analog Input Current

Input Buffers Disabled

Input Current ±6 µA/V

Input Current Drift External clock ±75 pA/V/°C

Internal clock (±2.5% clock) ±0.5 nA/V/°C

Input Buffers Enabled

Input Current ±5 nA

Input Current Drift ±0.1 nA/°C

Crosstalk 1 kHz input −120 dB

INTERNAL REFERENCE 100 nF external capacitor to AVSS

Output Voltage REFOUT, with respect to AVSS 2.5 V

Initial Accuracy3 REFOUT, TA = 25°C −0.12 +0.12 % of V

Temperature Coefficient1

0°C to 105°C ±2 ±5 ppm/°C

−40°C to +105°C ±3 ±10 ppm/°C

Reference Load Current, I

LOAD

−10

+10

Power Supply Rejection AVDD1, AVDD2 (line regulation) 90 dB

Load Regulation ∆VOUT/∆ILOAD 50 ppm/mA

Voltage Noise eN, 0.1 Hz to 10 Hz, 2.5 V reference 4.5 µV rms

Voltage Noise Density eN, 1 kHz, 2.5 V reference 215 nV/√Hz

Turn On Settling Time

100 nF REFOUT capacitor

200

µs

Short-Circuit Current, ISC 25 mA

Data Sheet AD7172-2

Rev. A | Page 5 of 60

Parameter Test Conditions/Comments Min Typ Max Unit

EXTERNAL REFERENCE INPUTS

Differential Input Range VREF = (REF+) − (REF−) 1 2.5 AVDD1 V

Absolute Voltage Limits1

Input Buffers Disabled AVSS − 0.05 AVDD1 + 0.05 V

Input Buffers Enabled AVSS AVDD1 V

REFIN Input Current

Input Buffers Disabled

Input Current

±9

µA/V

Input Current Drift External clock ±100 pA/V/°C

Internal clock ±0.75 nA/V/°C

Input Buffers Enabled

Input Current ±100 nA

Input Current Drift

±0.25

nA/°C

Normal Mode Rejection1 See the Rejection parameter

Common-Mode Rejection 95 dB

TEMPERATURE SENSOR

Accuracy

After user calibration at 25°C

±2

°C

Sensitivity 477 µV/K

BURNOUT CURRENTS

Source/Sink Current Analog input buffers must be enabled ±10 µA

GPIO (GPIO0, GPIO1) With respect to AVSS

Input Mode Leakage

Current1

−10

+10

µA

Floating State Output

Capacitance

5 pF

Output High Voltage, VOH1 ISOURCE = 200 µA AVSS + 4 V

Output Low Voltage, VOL1 ISINK = 800 µA AVSS + 0.4 V

Input High Voltage, VIH1 AVSS + 3 V

Input Low Voltage, VIL1 AVSS + 0.7 V

CLOCK

Internal Clock

Frequency 2 MHz

Accuracy −2.5% +2.5% %

Duty Cycle 50 %

Output Low Voltage, VOL 0.4 V

Output High Voltage, VOH 0.8 × IOVDD V

Crystal

Frequency 14 16 16.384 MHz

Startup Time

µs

External Clock (CLKIO) 2 2.048 MHz

Duty Cycle1 30 50 70 %

LOGIC INPUTS

Input High Voltage, VINH1 2 V ≤ IOVDD < 2.3 V 0.65 × IOVDD V

2.3 V ≤ IOVDD ≤ 5.5 V 0.7 × IOVDD V

Input Low Voltage, VINL1 2 V ≤ IOVDD < 2.3 V 0.35 × IOVDD V

2.3 V ≤ IOVDD ≤ 5.5 V 0.7 V

Hysteresis1 IOVDD ≥ 2.7 V 0.08 0.25 V

IOVDD < 2.7 V

0.04

0.2

Leakage Currents −10 +10 µA

AD7172-2 Data Sheet

Rev. A | Page 6 of 60

Parameter Test Conditions/Comments Min Typ Max Unit

LOGIC OUTPUT (DOUT/RDY)

Output High Voltage, VOH1 IOVDD ≥ 4.5 V, ISOURCE = 1 mA 0.8 × IOVDD V

2.7 V ≤ IOVDD < 4.5 V, ISOURCE = 500 µA 0.8 × IOVDD V

IOVDD < 2.7 V, ISOURCE = 200 µA 0.8 × IOVDD V

Output Low Voltage, VOL1 IOVDD ≥ 4.5 V, ISINK = 2 mA 0.4 V

2.7 V ≤ IOVDD < 4.5 V, ISINK = 1 mA 0.4 V

IOVDD < 2.7 V, ISINK = 400 µA 0.4 V

Leakage Current Floating state −10 +10 µA

Output Capacitance Floating state 10 pF

SYSTEM CALIBRATION1

Full-Scale (FS) Calibration

Limit

1.05 × FS V

Zero-Scale Calibration Limit −1.05 × FS V

Input Span 0.8 × FS 2.1 × FS V

POWER REQUIREMENTS

Power Supply Voltage

AVDD1 to AVSS 3.0 5.5 V

AVDD2 to AVSS

5.5

AVSS to DGND −2.75 0 V

IOVDD to DGND 2 5.5 V

IOVDD to AVSS

For AVSS < DGND

6.35

POWER SUPPLY CURRENTS4 All outputs unloaded, digital inputs connected

to IOVDD or DGND

Full Operating Mode

AVDD1 Current

AVDD1 = 5 V Typical,

5.5 V Maximum

AIN± and REF± buffers disabled; external

reference

0.23 0.27 mA

AIN± and REF± buffers disabled; internal

reference

0.4 0.48 mA

AIN± and REF± buffers enabled; internal

reference

1.9

2.35

Each buffer: AIN± and REF± 0.38 mA

AVDD1 = 3.3 V Typical,

3.6 V Maximum

AIN± and REF± buffers disabled; external

reference

0.15 0.19 mA

AIN± and REF± buffers disabled; internal

reference

0.33

0.39

AIN± and REF± buffers enabled; internal

reference

1.65 2.1 mA

Each buffer: AIN± and REF± 0.33 mA

AVDD2 Current External reference 1 1.1 mA

Internal reference 1.3 1.45 mA

IOVDD Current External clock 0.33 0.5 mA

Internal clock 0.61 0.82 mA

External crystal 0.98 mA

Standby Mode

Standby (LDO On) Reference off, total current consumption 32 µA

Reference on, total current consumption 420 µA

Power-Down Mode Full power-down, LDO, REF± 1 10 µA

Data Sheet AD7172-2

Rev. A | Page 7 of 60

Parameter Test Conditions/Comments Min Typ Max Unit

POWER DISSIPATION4

Full Operating Mode Unbuffered, external clock and reference;

AVDD1 = 3.3 V, AVDD2 = 2 V, IOVDD = 2 V

3.16 mW

Unbuffered, external clock and reference;

all supplies = 5 V

7.8 mW

Unbuffered, external clock and reference;

all supplies = 5.5 V

10.3 mW

Fully buffered, internal clock and reference

(note that REFOUT has no load); AVDD1 = 3.3 V,

AVDD2 = 2 V, IOVDD = 2 V

9.27

Fully buffered, internal clock and reference

(note that REFOUT has no load); all supplies = 5 V

19.1 mW

Fully buffered, internal clock and reference (note

that REFOUT has no load); all supplies = 5.5 V

25.4 mW

Standby Mode Reference off, all supplies = 5 V 160 µW

Reference on, all supplies = 5 V 2.1 mW

Power-Down Mode Full power-down, all supplies = 5 V 5 µW

Full power-down, all supplies = 5.5 V 55 µW

1 This specification is not production tested but is supported by characterization data at initial product release.

2 Following a system or internal zero-scale calibration, the offset error is in the order of the noise for the programmed output data rate selected. A system full-scale

calibration reduces the gain error to the order of the noise for the programmed output data rate.

3 This specification includes moisture sensitivity level (MSL) preconditioning effects.

4 These specifications are with no load on the REFOUT and digital output pins.

TIMING CHARACTERISTICS

IOVDD = 2 V to 5.5 V, DGND = 0 V, Input Logic 0 = 0 V, Input Logic 1 = IOVDD, CLOAD = 20 pF, unless otherwise noted.

Table 2.

Parameter Limit at TMIN, TMAX Unit Test Conditions/Comments1, 2

SCLK

t3 25 ns min SCLK high pulse width

ns min

SCLK low pulse width

READ OPERATION

t1 0 ns min CS falling edge to DOUT/RDY active time

15 ns max IOVDD = 4.75 V to 5.5 V

ns max

IOVDD = 2 V to 3.6 V

t23 0 ns min SCLK active edge to data valid delay4

12.5 ns max IOVDD = 4.75 V to 5.5 V

25 ns max IOVDD = 2 V to 3.6 V

t5 2.5 ns min Bus relinquish time after CS inactive edge

20 ns max

t6 0 ns min SCLK inactive edge to CS inactive edge

t75 10 ns min SCLK inactive edge to DOUT/RDY high/low

WRITE OPERATION

ns min

CS falling edge to SCLK active edge setup time4

t9 8 ns min Data valid to SCLK edge setup time

t10 8 ns min Data valid to SCLK edge hold time

t11 5 ns min CS rising edge to SCLK edge hold time

1 Sample tested during initial release to ensure compliance.

2 See Figure 2 and Figure 3.

3 This parameter is defined as the time required for the output to cross the VOL or VOH limits.

4 The SCLK active edge is the falling edge of SCLK.

5 DOUT/RDY returns high after a read of the data register. In single conversion mode and continuous conversion mode, the same data can be read again, if required,

while DOUT/RDY is high, although care must be taken to ensure that subsequent reads do not occur close to the next output update. If the continuous read feature is

enabled, the digital word can be read only once.

Data Sheet AD7172-2

Rev. A | Page 8 of 60

TIMING DIAGRAMS

CS (I)

DOUT/RDY (O)

SCLK (I)

I = INPUT, O = OUTPUT

MSB LSB

12672-003

Figure 2. Read Cycle Timing Diagram

I = INPUT, O = OUTPUT

CS (I)

SCLK (I)

DIN (I) MSB LSB

t10

t11

12672-004

Figure 3. Write Cycle Timing Diagram

Data Sheet AD7172-2

Rev. A | Page 9 of 60

ABSOLUTE MAXIMUM RATINGS

TA = 25°C, unless otherwise noted.

Table 3.

Parameter Rating

AVDD1, AVDD2 to AVSS −0.3 V to +6.5 V

AVDD1 to DGND −0.3 V to +6.5 V

IOVDD to DGND −0.3 V to +6.5 V

IOVDD to AVSS −0.3 V to +7.5 V

AVSS to DGND −3.25 V to +0.3 V

Analog Input Voltage to AVSS −0.3 V to AVDD1 + 0.3 V

Reference Input Voltage to AVSS

−0.3 V to AVDD1 + 0.3 V

Digital Input Voltage to DGND −0.3 V to IOVDD + 0.3 V

Digital Output Voltage to DGND −0.3 V to IOVDD + 0.3 V

Analog Input/Digital Input Current 10 mA

Operating Temperature Range −40°C to +105°C

Storage Temperature Range −65°C to +150°C

Maximum Junction Temperature 150°C

Lead Soldering, Reflow Temperature 260°C

ESD Rating (HBM) 4 kV

Stresses at or above those listed under Absolute Maximum

Ratings may cause permanent damage to the product. This is a

stress rating only; functional operation of the product at these

or any other conditions above those indicated in the operational

section of this specification is not implied. Operation beyond

the maximum operating conditions for extended periods may

affect product reliability.

THERMAL RESISTANCE

θJA is specified for a device soldered on a JEDEC test board for

surface-mount packages.

Table 4. Thermal Resistance

Package Type θJA Unit

24-Lead TSSOP

1-Layer JEDEC Board

149

°C/W

2-Layer JEDEC Board

°C/W

ESD CAUTION

AD7172-2 Data Sheet

Rev. A | Page 10 of 60

PIN CONFIGURATION AND FUNCTION DESCRIPTIONS

REF–

REF+

REFOUT

AVDD1

AVSS

REGCAPA

AIN4

AVDD2

XTAL1

DIN

DOUT/RDY

XTAL2/CLKIO

AIN2

AIN1

AIN0

REGCAPD

GPIO0

GPIO1

DGND

IOVDD

SCLK

SYNC/ERROR

AIN3

AD7172-2

TOP VIEW

(Not to Scale)

12672-002

Figure 4. Pin Configuration

Table 5. Pin Function Descriptions

Pin No. Mnemonic Type 1 Description

1 AIN4 AI Analog Input 4. Analog Input 4 is selectable through the crosspoint multiplexer.

2 REF− AI Reference Input Negative Terminal. REF− can span from AVSS to AVDD1 − 1 V.

3 REF+ AI

Reference Input Positive Terminal. An external reference can be applied between REF+ and REF−. REF+

can span from AVSS + 1 V to AVDD1.The device functions with a reference magnitude from 1 V to

AVDD1.

4 REFOUT AO Buffered Output of Internal Reference. The output is 2.5 V with respect to AVSS.

5 REGCAPA AO Analog LDO Regulator Output. Decouple this pin to AVSS using a 1 µF and a 0.1 µF capacitor.

6 AVSS P Negative Analog Supply. This supply ranges from −2.75 V to 0 V and is nominally set to 0 V.

7 AVDD1 P Analog Supply Voltage 1. This voltage is 3.3 V or 5 V ± 10% with respect to AVSS.

AVDD2

Analog Supply Voltage 2. This voltage ranges from 2 V to 5.5 V with respect to AVSS.

9 XTAL1 AI Input 1 for Crystal.

10 XTAL2/CLKIO AI/

DI/O

Input 2 for Crystal/Clock Input or Output. Based on the CLOCKSEL bits in the ADCMODE register. The

following four options are available for selecting the MCLK source:

Internal oscillator: no output.

Internal oscillator: output to XTAL2/CLKIO. Operates at IOVDD logic level.

External clock: input to XTAL2/CLKIO. Input must be at IOVDD logic level.

External crystal: connected between XTAL1 and XTAL2/CLKIO.

11 DOUT/RDY DO Serial Data Output/Data Ready Output. DOUT/RDY is a dual purpose pin. This pin functions as a serial data

output pin to access the output shift register of the ADC. The output shift register can contain data from

any of the on-chip data or control registers. The data-word/control word information is placed on the

DOUT/RDY pin on the SCLK falling edge and is valid on the SCLK rising edge. When CS is high, the

DOUT/RDY output is three-stated. When CS is low, DOUT/RDY operates as a data ready pin, going low

to indicate the completion of a conversion. If the data is not read after the conversion, the pin goes

high before the next update occurs. The DOUT/RDY falling edge can be used as an interrupt to a

processor, indicating that valid data is available.

12 DIN DI Serial Data Input to the Input Shift Register on the ADC. Data in this shift register is transferred to the

control registers in the ADC, with the register address (RA) bits of the communications register

identifying the appropriate register. Data is clocked in on the rising edge of SCLK.

13 SCLK DI Serial Clock Input. This serial clock input is for data transfers to and from the ADC. The SCLK has a

Schmitt triggered input, making the interface suitable for opto-isolated applications.

14 CS DI Chip Select Input. This is an active low logic input selects the ADC. CS can select the ADC in systems

with more than one device on the serial bus. CS can be hardwired low, allowing the ADC to operate in 3-

wire mode with the SCLK, DIN, and DOUT pins interfacing with the device. When CS is high, the

DOUT/RDY output is three-stated.

Data Sheet AD7172-2

Rev. A | Page 11 of 60

Pin No. Mnemonic Type 1 Description

15 SYNC/ERROR DI/O Synchronization Input/Error Input/Output. This pin can be switched between a logic input and a logic

output in the GPIOCON register. When synchronization input (SYNC) is enabled, this pin allows

synchronization of the digital filters and analog modulators when using multiple AD7172-2 devices.

For more information, see the Synchronization section. When the synchronization input is disabled,

this pin can be used in one of the following three modes:

Active low error input mode: this mode sets the ADC_ERROR bit in the status register.

Active low, open-drain error output mode: the status register error bits are mapped to the ERROR

output. The SYNC/ERROR pins of multiple devices can be wired together to a common pull-up resistor

so that an error on any device can be observed.

General-purpose output mode: the status of the pin is controlled by the ERR_DAT bit in the GPIOCON

used by the GPIOx pins. The pin has an active pull-up in this case.

16 IOVDD P Digital Input/Output Supply Voltage. The IOVDD voltage ranges from 2 V to 5.5 V. IOVDD is

independent of AVDD2. For example, IOVDD can be operated at 3 V when AVDD2 equals 5 V, or vice

versa. If AVSS is set to −2.5 V, the voltage on IOVDD must not exceed 3.6 V.

DGND

Digital Ground.

18 REGCAPD AO Digital LDO Regulator Output. This pin is for decoupling purposes only. Decouple this pin to DGND

using a 1 µF and a 0.1 µF capacitor.

19 GPIO0 DI/O General-Purpose Input/Output 0. The pin is referenced between the AVDD1 and AVSS levels.

20 GPIO1 DI/O General-Purpose Input/Output 1. The pin is referenced between the AVDD1 and AVSS levels.

21 AIN0 AI Analog Input 0. Analog Input 0 is selectable through the crosspoint multiplexer.

AIN1

Analog Input 1. Analog Input1 is selectable through the crosspoint multiplexer.

23 AIN2 AI Analog Input 2. Analog Input 2 is selectable through the crosspoint multiplexer.

24 AIN3 AI Analog Input 3. Analog Input 3 is selectable through the crosspoint multiplexer.

1 AI is analog input, AO is analog output, DI/O is bidirectional digital input/output, DO is digital output, DI is digital input, and P is power supply.

AD7172-2 Data Sheet

Rev. A | Page 12 of 60

TYPICAL PERFORMANCE CHARACTERISTICS

AVDD1 = 5 V, AVDD2 = 5 V, IOVDD = 3.3 V, TA = 25°C, unless otherwise noted.

0200 400 600 800 1000

ADC CODE

SAMPLE NUMBER

8388478

8388480

8388482

8388484

8388486

8388488

8388490

8388492

12672-205

Figure 5. Noise (Analog Input Buffers Disabled, VREF = 5 V,

Output Data Rate = 1.25 SPS)

0200 400 600 800 1000100 300 500 700 900

ADC CODE

OCCURENCE

8388460

8388465

8388470

8388475

8388480

8388485

8388490

8388495

8388500

8388505

8388510

12672-206

Figure 6. Noise (Analog Input Buffers Disabled, VREF = 5 V,

Output Data Rate = 2.6 kSPS)

0200 400 600 800 1000100 300 500 700 900

ADC CODE

OCCURENCE

8388440

8388450

8388460

8388470

8388480

8388490

8388500

8388510

8388520

8388530

8388540

12672-207

Figure 7. Noise (Analog Input Buffers Disabled, VREF = 5 V,

Output Data Rate = 31.25 kSPS)

OCCURENCE

ADC CODE

1200

1000

800

600

400

200

8388480 8388482 8388484 8388486 8388488 8388490 8388492

12672-208

Figure 8. Histogram (Analog Input Buffers Disabled, VREF = 5 V,

Output Data Rate = 1.25 SPS)

OCCURENCE

ADC CODE

140

120

100

8388465

8388467

8388469

8388471

8388473

8388475

8388477

8388479

8388481

8388483

8388485

8388487

8388489

8388491

8388493

8388495

8388497

8388499

8388501

8388503

8388505

12672-209

Figure 9. Histogram (Analog Input Buffers Disabled, VREF = 5 V,

Output Data Rate = 2.6 kSPS)

OCCURENCE

ADC CODE

100

8388446

8388449

8388452

8388455

8388458

8388461

8388464

8388467

8388470

8388473

8388476

8388479

8388482

8388485

8388488

8388491

8388494

8388497

8388500

8388503

8388506

8388509

8388512

8388515

8388518

8388521

8388524

8388527

8388530

8388533

12672-210

Figure 10. Histogram (Analog Input Buffers Disabled, VREF = 5 V,

Output Data Rate = 31.25 kSPS)

Data Sheet AD7172-2

Rev. A | Page 13 of 60

0200 400 600 800 1000

ADC CODE

SAMPLE NUMBER

8388481

8388483

8388485

8388487

8388489

8388491

8388493

8388495

12672-211

Figure 11. Noise (Analog Input Buffers Enabled, VREF = 5 V,

Output Data Rate = 1.25 SPS)

0200 400 600 800 1000100 300 500 700 900

ADC CODE

OCCURENCE

8388460

8388470

8388480

8388490

8388500

8388510

8388520

12672-212

Figure 12. Noise (Analog Input Buffers Enabled, VREF = 5 V,

Output Data Rate = 2.6 kSPS)

200 400 600 800 1000100 300 500 700 900

ADC CODE

OCCURENCE

8388400

8388420

8388440

8388460

8388480

8388500

8388520

8388540

8388560

12672-213

Figure 13. Noise (Analog Input Buffers Enabled, VREF = 5 V,

Output Data Rate = 31.25 kSPS)

OCCURENCE

ADC CODE

1200

1000

800

600

400

200

8388482 8388484 8388486 8388488

8388490 8388494

8388492

12672-214

Figure 14. Histogram (Analog Input Buffers Enabled, VREF = 5 V,

Output Data Rate = 1.25 SPS)

OCCURENCE

ADC CODE

120

100

8388462

8388464

8388466

8388468

8388470

8388472

8388474

8388476

8388478

8388480

8388482

8388484

8388486

8388488

8388490

8388492

8388494

8388496

8388498

8388500

8388502

8388504

8388506

8388508

8388510

8388512

8388514

8388516

12672-215

Figure 15. Histogram (Analog Input Buffers Enabled, VREF = 5 V,

Output Data Rate = 2.6 kSPS)

OCCURENCE

ADC CODE

120

100

8388422

8388430

8388438

8388446

8388454

8388462

8388470

8388478

8388486

8388494

8388502

8388510

8388518

8388526

8388534

8388542

12672-216

Figure 16. Histogram (Analog Input Buffers Enabled, VREF = 5 V,

Output Data Rate = 31.25 kSPS)

AD7172-2 Data Sheet

Rev. A | Page 14 of 60

NOISE (V rms)

FREQUENCY (MHz)

1000

201000

401000

601000

801000

1001000

1201000

1401000

1601000

1801000

ANALOG INPUT BUFFERS OFF

ANALOG INPUT BUFFERS ON

12672-218

Figure 17. Noise vs. External Master Clock Frequency,

Analog Input Buffers On and Off

110 100 1k 10k 100k 1M

CMRR (dB)

VIN FREQUENCY (Hz)

–140

–120

–100

–80

–60

–40

–20

12672-224

Figure 18. Common-Mode Rejection Ratio (CMRR) vs. VIN Frequency

(VIN = 0.1 V, Output Data Rate = 31.25 kSPS)

10 20 30 40 50 60 70

CMRR (dB)

FREQUENCY (Hz)

–180

–160

–140

–120

–100

–80

–60

–40

–20

12672-225

Figure 19. Common-Mode Rejection Ratio (CMRR) vs. VIN Frequency

(VIN = 0.1 V, 10 Hz to 70 Hz, Output Data Rate = 20 SPS, Enhanced Filter)

110 100 1k 10k 100k 100M10M1M

PSRR (dB)

FREQUENCY (Hz)

12672-226

–150

–140

–130

–120

–110

–100

–90

–80

–70

–60

Figure 20. Power Supply Rejection Ratio (PSRR) vs. VIN Frequency

–5 –4 –3 –2 –1 0 1 2 3 4 5

INL (ppm/FS)

(V)

–6

–4

–2

INTERNAL 2.5V REFERENCE, ANALOG INPUT BUFFERS OFF

INTERNAL 2.5V REFERENCE, ANALOG INPUT BUFFERS ON

EXT-CRYSTAL BUFFERS OFF

EXT-CRYSTAL BUFFERS ON

EXT CLK BUFFERS OFF

EXT CLK BUFFERS ON

12672-227

EXTERNAL 2.5V REFERENCE, ANALOG INPUT BUFFERS OFF

EXTERNAL 2.5V REFERENCE, ANALOG INPUT BUFFERS ON

EXTERNAL 5V REFERENCE, ANALOG INPUT BUFFERS OFF

EXTERNAL 5V REFERENCE, ANALOG INPUT BUFFERS ON

Figure 21. Integral Nonlinearity (INL) vs. VIN (Differential Input)

OCCURENCE

INL (ppm)

0.75 1.00 1.25 1.50 1.75 2.00 2.25 2.50 2.75 3.00 3.25

12672-228

Figure 22. INL Distribution Histogram (Differential Input, Analog Input

Buffers Enabled, VREF = 2.5 V External, 100 Units)

Data Sheet AD7172-2

Rev. A | Page 15 of 60

OCCURENCE

INL (ppm)

0.50 0.75 1.00 1.25 1.50 1.75 2.00 2.25 2.50 2.75 3.00

12672-229

Figure 23. INL Distribution Histogram (Differential Input, Analog Input

Buffers Disabled, VREF = 2.5 V External, 100 Units)

OCCURENCE

INL (ppm)

0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

12672-230

Figure 24. INL Distribution Histogram (Analog Input Buffers Enabled,

Differential Input, VREF = 5 V External, 100 Units)

OCCURENCE

INL (ppm)

0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

12672-231

Figure 25. INL Distribution Histogram (Analog Input Buffers Disabled,

Differential Input, VREF = 5 V External, 100 Units)

–40–30–20–100 102030405060708090100

INL (ppm)

TE M P E R ATURE (°C)

5.0

4.5

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

BUFFERS ON

BUFFERS OFF

12672-232

Figure 26. INL vs. Temperature (Differential Input, VREF = 2.5 V External)

OCCURENCE

FRE Q UE NCY ( M Hz)

1.996 1.997 1.998 1.999 2.00 2.001 2.002 2.003

12672-233

Figure 27. Internal Oscillator Frequency Distribution Histogram (100 Units)

–40–30–20–100 102030405060708090100

FREQ UENCY (Hz )

TE M P E R ATURE (°C)

1.95

1.96

1.97

1.98

1.99

2.00

2.01

12672-234

Figure 28. Internal Oscillator Frequency vs. Temperature

AD7172-2 Data Sheet

Rev. A | Page 16 of 60

–40 –30 –20 –10 010 20 30 40 50 60 70 80 90 100

ERROR (V)

TEMPERATURE (°C)

–0.0015

–0.0010

–0.0005

0.0005

0.0010

0.0015

12672-235

Figure 29. Absolute Reference Error vs. Temperature

OCCURENCE

OFFSET (µV)

–50 –40 –30 –20 –10 010 20 30 40 50 60 70

12672-236

Figure 30. Offset Error Distribution Histogram

(Internal Short, 100 Units)

OCCURENCE

OFFSET DRIFT (nV/°C)

–50 –40 –30 –20 –10 010 20 30 40 50 60 1101008070 90

12672-237

Figure 31. Offset Error Drift Distribution Histogram

(Internal Short, 100 Units)

OCCURENCE

GAIN ERROR (ppm of FSR)

–8 –7 –6 –5 –4 –3 –2 –1 01 2 3 6

12672-238

Figure 32. Gain Error Distribution Histogram

(Analog Input Buffers Enabled, 100 Units)

OCCURENCE

GAIN ERROR (ppm of FSR)

–7 –6 –5 –4 –3 –2 –1 0 1 2 3 654

12672-239

Figure 33. Gain Error Distribution Histogram

(Analog Input Buffers Disabled, 100 Units)

OCCURENCE

GAIN DRIFT (ppm/°C)

–0.2 –0.1 00.1 0.2 0.3 0.4 0.5

12672-240

Figure 34. Gain Drift Distribution Histogram

(Analog Input Buffers Enabled, 100 Units)

Data Sheet AD7172-2

Rev. A | Page 17 of 60

OCCURENCE

GAIN DRIFT (ppm/°C)

–0.05 00.05 0.10 0.15 0.20 0.25

12672-241

Figure 35. Gain Drift Distribution Histogram

(Analog Input Buffers Disabled, 100 Units)

–40 –30 –20 –10 010 20 30 40 50 60 70 80 90 100

CURRENT (mA)

TEMPERATURE (°C)

ALL BUFFERS ENABLED

ALL BUFFERS DISABLED

12672-242

Figure 36. Current Consumption vs. Temperature

(Continuous Conversion Mode)

–40 –30 –20 –10 010 20 30 40 50 60 70 80 90 100

CURRENT (µA)

TEMPERATURE (°C)

700

600

500

400

300

200

100

REFERENCE ENABLED

REFERENCE DISABLED

12672-243

Figure 37. Current Consumption vs. Temperature

(Standby Mode)

–2.0 –1.6 –1.2 –0.8 –0.4 00.4 0.8 1.2

OCCURENCE

TEMPERATURE DELTA (°C)

12672-244

Figure 38. Temperature Sensor Distribution Histogram

(Uncalibrated, 100 Units)

AD7172-2 Data Sheet

Rev. A | Page 18 of 60

9.5 10.5

10.410.3

10.2

10.110.0

9.99.89.79.6

OCCURENCE

CURRENT (µA)

12672-245

Figure 39. Burnout Current Distribution Histogram (100 Units)

INPUT CURRENT (nA)

INPUT VOLTAGE (V)

–10

–5

–5.00

–4.62

–4.29

–3.96

–3.63

–3.30

–2.97

–2.64

–2.31

–1.98

–1.65

–1.32

–990.00m

–660.00m

–330.00m

330.00m

660.00m

990.00m

1.32

1.65

1.98

2.31

2.64

2.97

3.30

3.63

3.96

4.29

4.62

5.00

–40°C, AIN–

–40°C, AIN+

+25°C, AIN–

+25°C, AIN+

+85°C, AIN–

+85°C, AIN+

+105°C, AIN–

12672-246

Figure 40. Analog Input Current vs. Input Voltage (VCM = 2.5 V)

–40 –30 –20 –10 010 20 30 40 50 60 70 80 90 100

CURRENT (nA)

TEMPERATURE (°C)

–15

–5

–10

12672-247

AIN+=AVDD1–0.2V

AIN

–=AVSS + 0.2 V

AIN+=AVDD1

AIN– =AVSS

Figure 41. Analog Input Current vs. Temperature

Data Sheet AD7172-2

Rev. A | Page 19 of 60

NOISE PERFORMANCE AND RESOLUTION

Table 6 and Table 7 show the rms noise, peak-to-peak noise,

effective resolution, and the noise free (peak-to-peak) resolution

of the AD7172-2 for various output data rates and filters. The

numbers given are for the bipolar input range with an external

5 V reference. These numbers are typical and are generated with

a differential input voltage of 0 V when the ADC is

continuously converting on a single channel. It is important to

note that the peak-to-peak resolution is calculated based on the

peak-to-peak noise. The peak-to-peak resolution represents the

resolution for which there is no code flicker.

Table 6. RMS Noise and Peak-to-Peak Resolution vs. Output Data Rate Using Sinc5 + Sinc1 Filter (Default)1

Output Data Rate (SPS) RMS Noise (µV rms) Effective Resolution (Bits) Peak-to-Peak Noise (µV p-p) Peak-to-Peak Resolution (Bits)

Input Buffers Disabled

31,250 8.2 20.2 66 17.2

15,625 7.0 20.4 52 17.5

10,417 6.0 20.7 45 17.8

1007 2.2 22.2 15 19.3

59.52 0.48 24 3.2 21.6

49.68 0.47 24 3.1 21.6

16.63 0.25 24 1.6 22.6

1.25 0.088 24 0.32 24

Input Buffers Enabled

31,250 9.5 20 74 17

15,625 8.2 20.2 63 17.3

10,417 7.1 20.4 53 17.5

1007 2.6 21.9 16 19.3

59.52 0.62 24 3.6 21.4

49.68 0.53 24 3.3 21.5

16.63

0.32

1.7

22.2

1.25 0.089 24 0.35 24

1 Selected rates only, 1000 samples.

Table 7. RMS Noise and Peak-to-Peak Resolution vs. Output Data Rate Using Sinc3 Filter1

Output Data Rate (SPS) RMS Noise (µV rms) Effective Resolution (Bits) Peak-to-Peak Noise (µV p-p) Peak-to-Peak Resolution (Bits)

Input Buffers Disabled

31,250 211 15.5 1600 12.5

15,625 27.2 18.5 205 15.6

10,417 7.9 20.3 57 17.4

1008 1.6 22.6 11 19.8

59.98 0.38 24 2.5 21.9

50 0.35 24 2.3 22

16.67 0.21 24 1.1 23.1

1.25 0.054 24 0.27 24

Input Buffers Enabled

31,250 212 15.5 1600 12.5

15,625

27.7

18.5

210

15.5

10,417 8.5 20.2 63 17.3

1008 1.8 22.4 13 19.6

59.98 0.45 24 2.8 21.8

50 0.44 24 2.5 22

16.67

0.24

1.2

1.25 0.073 24 0.29 24

1 Selected rates only, 1000 samples.

AD7172-2 Data Sheet

Rev. A | Page 20 of 60

GETTING STARTED

The AD7172-2 offers the user a fast settling, high resolution,

multiplexed ADC with high levels of configurability, including

the following features:

• Two fully differential or four single-ended analog inputs.

• A crosspoint multiplexer selects any analog input combina-

tion as the input signals to be converted, routing them to

the modulator positive or negative input.

• True rail-to-rail buffered analog and reference inputs.

• Fully differential input or single-ended input relative to any

analog input.

• Per channel configurability—up to four different setups

can be defined. A separate setup can be mapped to each of

the channels. Each setup allows the user to configure

whether the buffers are enabled or disabled, gain and offset

correction, filter type, output data rate, and reference

source selection (internal or external).

The AD7172-2 includes a precision, 2.5 V, low drift (±2 ppm/°C)

band gap internal reference. This reference can be used for the

ADC conversions, reducing the external component count.

Alternatively, the reference can be output to the REFOUT pin to

be used as a low noise biasing voltage for external circuitry. An

example of this is using the REFOUT signal to set the input

common mode for an external amplifier.

The AD7172-2 includes two separate linear regulator blocks for

both the analog and digital circuitry. The analog LDO regulator

regulates the AVDD2 supply to 1.8 V, supplying the ADC core.

The user can tie the AVDD1 and AVDD2 supplies together for

easiest connection. If there is already a clean analog supply rail

in the system in the range of 2 V (minimum) to 5.5 V

(maximum), the user can also choose to connect this supply to

the AVDD2 input, allowing lower power dissipation.

DGND

AD7172-2

IOVDD

SYNC/ERROR

REGCAPD

REFOUT

AVSS

0.1µF

REGCAPA

AVDD2

AVDD1

XTAL1

GPIO1

19 20

REF–

REF+

2.5V REFERENCE

OUTPUT

4.7µF0.1µF

0.1µF

OUT

GND

NCV

0.1µF

4.7µF

0.1µF

ADR445BRZ

IOVDD

AVDD2

0.1µF

AVDD1

0.1µF

CX1

16MHz

CX2

0.1µF

1µF

0.1µF 1µF

GENERAL-PURPOSE I/O 0 AND

GENERAL-PURPOSE I/O 1

OUTPUT HIGH = AVDDx

OUTPUT LOW = AVSS

OPTIONAL EXTERNAL

CRYSTAL CIRCUITRY

CAPACITORS

GPIO0

CLKIN

OPTIONAL

EXTERNAL

CLOCK

INPUT

AIN0

AIN1

AIN2

AIN3

AIN4

GPIO0 GPIO1

XTAL2/CLKIO

DOUT/RDY

DIN

SCLK

SYNC/ERROR

DOUT/RDY

DIN

SCLK

0.1µF

12672-051

TP NC

TPTRIM

Figure 42. Typical Connection Diagram

Data Sheet AD7172-2

Rev. A | Page 21 of 60

The linear regulator for the digital IOVDD supply regulates the

input voltage applied at the IOVDD pin to 1.8 V for the internal

digital filtering. The serial interface signals always operate from

the IOVDD supply seen at the pin; if 3.3 V is applied to the

IOVDD pin, the interface logic inputs and outputs operate at

this level.

The AD7172-2 can be used across a wide variety of applications,

providing high resolution and accuracy. A sample of these

scenarios is as follows:

• Fast scanning of analog input channels using the internal

multiplexer

• Fast scanning of analog input channels using an external

multiplexer with automatic control from the GPIOs

• High resolution at lower speeds in either channel scanning

or ADC per channel applications

• Single ADC per channel: the fast low latency output allows

further application specific filtering in an external micro-

controller, DSP, or field programmable gate array (FPGA)

POWER SUPPLIES

The AD7172-2 has three independent power supply pins: AVDD1,

AVDD2, and IOVDD. AVDD1 powers the crosspoint multiplexer

and integrated analog and reference input buffers. AVDD1 is

referenced to AVSS, and AVDD1 − AVS S = 3.3 V or 5 V. AVDD1

and AVS S can be a single 3.3 V or 5 V supply or a ±1.65 V or

±2.5 V split supply. The split supply operation allows true bipolar

inputs. When using split supplies, consider the absolute maximum

ratings (see the Absolute Maximum Ratings section).

AVDD2 powers the internal 1.8 V analog LDO regulator. This

regulator powers the ADC core. AVDD2 is referenced to AVSS,

and AVDD2 to AVSS can range from 5.5 V (maximum) to 2 V

(minimum).

IOVDD powers the internal 1.8 V digital LDO regulator. This

regulator powers the digital logic of the ADC. IOVDD sets the

voltage levels for the SPI interface of the ADC. IOVDD is refer-

enced to DGND, and IOVDD to DGND can vary from 5.5 V

(maximum) to 2 V (minimum).

There is no specific requirement for a power supply sequence

on the AD7172-2. When all power supplies are stable, a device

reset is required; see the AD7172-2 Reset section for details on

how to reset the device.

Recommended Linear Regulators

The ADP7118 provides positive supply rails to the AD7172-2,

creating either a single 5 V, 3.3 V, or dual AVDD1/IOVDD,

depending on the required supply configuration. The ADP7118

can operate from input voltages up to 20 V.

12672-100

ADP7118

LDO 5V: AVDD1

ADP7118

LDO 3.3V: AVDD2/IOVDD

12V

INPUT

Figure 43. Single Supply Linear Regulator

The ADM660 and ADP7182 generate a clean negative rail for

AVSS in the bipolar configuration to provide optimal converter

performance.

ADP7118

LDO +2.5V: AVDD1/AVDD2

ADP7118

LDO +3.3V: IOVDD

ADP7182

LDO

ADM660

LDO –2.5V: AVSS

INPUT

–5V

12672-101

Figure 44. Bipolar AD7172-2 Supply Rails

Table 8. Recommended Power Management Devices

Product

Description

ADP7118 20 V, 200 mA, low noise, CMOS LDO regulator

ADP7182

−28 V, −200 mA, low noise, linear regulator

ADM660 CMOS switched-capacitor voltage converter

DIGITAL COMMUNICATION

The AD7172-2 has a 3- or 4-wire SPI interface that is compatible

with QSPI™, MICROWIRE, and DSPs. The interface operates in

SPI Mode 3 and can be operated with CS tied low. In SPI Mode 3,

the SCLK idles high, the falling edge of SCLK is the drive edge,

and the rising edge of SCLK is the sample edge. This means that

data is clocked out on the falling/drive edge and data is clocked

in on the rising/sample edge.

DRIVE EDGE SAMPLE EDGE

12672-052

Figure 45. SPI Mode 3 SCLK Edges

Accessing the ADC Register Map

The communications register controls access to the full register

map of the ADC. This register is an 8-bit write only register. On

power-up or after a reset, the digital interface defaults to a state

where it is expecting a write to the communications register;

therefore, all communication begins by writing to the

communications register.

The data written to the communications register determines

which register is being accessed and if the next operation is a read

or write. The register address bits (RA, Bits[5:0] in Register 0x00)

determine the specific register to which the read or write

operation applies.

When the read or write operation to the selected register is

complete, the interface returns to the default state, where it

expects a write operation to the communications register.

Figure 46 and Figure 47 illustrate writing to and reading from a

AD7172-2 Data Sheet

Rev. A | Page 22 of 60

DIN

SCLK

8-BIT COMMAND

8 BITS, 16 BITS,

OR 24 BITS OF DATA

CMD DATA

12672-053

Figure 46. Writing to a Register

(8-Bit Command with Register Address Followed by Data of 8, 16, or 24 Bits;

Data Length on DIN Is Dependent on the Register Selected)

DIN

SCLK

8-BIT COMMAND

8 BITS, 16 BITS,

24 BITS, OR

32 BITS OUTPUT

CMD

DATA

DOUT/RDY

12672-054

Figure 47. Reading from a Register

(8-Bit Command with Register Address Followed by Data of 8, 16, or 24 Bits;

Data Length on DOUT/RDY Is Dependent on the Register Selected)

Reading the ID register is the recommended method for verifying

correct communication with the device. The ID register is a

read only register and contains the value 0x00DX for the

AD7172-2. The communications register and the ID register details

are described in Table 9 and Table 10.

AD7172-2 RESET

After a power-up cycle and when the power supplies are stable,

a device reset is required. In situations where interface synchro-

nization is lost, a device reset is also required. A write operation

of at least 64 serial clock cycles with DIN high returns the ADC to

the default state by resetting the entire device, including the register

contents. Alternatively, if CS is being used with the digital interface,

returning CS high sets the digital interface to the default state and

halts any serial interface operation.

CONFIGURATION OVERVIEW

After power-on or reset, the AD7172-2 default configuration is

as follows:

• Channel configuration: CH0 is enabled, AIN0 is selected

as the positive input, and AIN1 is selected as the negative

input. Setup 0 is selected.

• Setup configuration: The internal reference and the analog

input buffers are disabled. The reference input buffers are

also disabled. An external reference on the REF± pins is

selected.

• Filter configuration: The sinc5 + sinc1 filter is selected and

the maximum output data rate of 31.25 kSPS is selected.

• ADC mode: Continuous conversion mode and the internal

oscillator are enabled.

• Interface mode: CRC and data + status output are disabled.

Note that only a few of the register setting options are shown;

this list is just an example. For full register information, see the

Figure 48 shows an overview of the suggested flow for changing

the ADC configuration, divided into the following three blocks:

• Channel configuration (see Box A in Figure 48)

• Setup configuration (see Box B in Figure 48)

• ADC mode and interface mode configuration (see Box C

in Figure 48)

Channel Configuration

The AD7172-2 has four independent channels and four independ-

ent setups. The user can select any of the analog input pairs on

any channel, as well as any of the four setups for any channel,

giving the user full flexibility in the channel configuration. This

also allows per channel configuration when using differential

inputs and single-ended inputs because each channel can have a

dedicated setup.

Channel Registers

The channel registers select which of the five analog input pins

(AIN0 to AIN4) are used as either the positive analog input

(AIN+) or the negative analog input (AIN−) for that channel.

This register also contains a channel enable/disable bit and the

setup selection bits, which select which of the four available

setups to use for this channel.

When the AD7172-2 is operating with more than one channel

enabled, the channel sequencer cycles through the enabled

channels in sequential order, from Channel 0 to Channel 3. If a

channel is disabled, it is skipped by the sequencer. Details of the

channel register for Channel 0 are shown in Table 11.

Data Sheet AD7172-2

Rev. A | Page 23 of 60

ADC MODE AND INTERFACE MODE CONFIGURATION

SELECT ADC OPERATING MODE, CLOCK SOURCE,

ENABLE CRC, DATA + STATUS, AND MORE

SETUP CONFIGURATION

4 POSSIBLE ADC SETUPS

SELECT FILTER ORDER, OUTPUT DATA RATE, AND MORE

CHANNEL CONFIGURATION

SELECT POSITIVE AND NEGATIVE INPUT FOR EACH ADC CHANNEL

SELECT ONE OF 4 SETUPS FOR ADC CHANNEL

12672-044

Figure 48. Suggested ADC Configuration Flow

Table 9. Communications Register

Reg. Name Bits Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Reset RW

0x00

COMMS

[7:0]

WEN R/W

0x00

Table 10. ID Register

Reg. Name Bits Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Reset RW

0x07 ID [15:8] ID[15:8] 0x00DX R

[7:0] ID[7:0]

Table 11. Channel 0 Register

Reg. Name Bits Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Reset RW

0x10 CH0 [15:8] CH_EN0 Reserved SETUP_SEL0 Reserved AINPOS0[4:3] 0x8001 RW

[7:0] AINPOS0[2:0] AINNEG0

AD7172-2 Data Sheet

Rev. A | Page 24 of 60

ADC Setups

The AD7172-2 has four independent setups. Each setup consists

of the following four registers:

• Setup configuration register

• Filter configuration register

• Gain register

• Offset register

For example, Setup 0 consists of Setup Configuration Register 0,

Filter Configuration Register 0, Gain Register 0, and Offset

setup is selectable from the channel registers (see the Channel

Configuration section), which allows each channel to be

assigned to one of four separate setups. Table 12 through Table 15

show the four registers that are associated with Setup 0. This

structure is repeated for Setup 1 to Setup 3.

Setup Configuration Registers

The setup configuration registers allow the user to select the output

coding of the ADC by selecting between bipolar mode and

unipolar mode. In bipolar mode, the ADC accepts negative

differential input voltages, and the output coding is offset binary. In

unipolar mode, the ADC accepts only positive differential voltages,

and the coding is straight binary. In either case, the input voltage

must be within the AVDD1/AVSS supply voltages. The user can

select the reference source using these registers. Three options

are available: an internal 2.5 V reference, an external reference

connected between the REF+ and REF− pins, or AVDD1 −

AVSS. The analog input and reference input buffers can also be

enabled or disabled using these registers.

Filter Configuration Registers

The filter configuration registers select which digital filter is

used at the output of the ADC modulator. The order of the filter

and the output data rate is selected by setting the bits in these

registers. For more information, see the Digital Filters section.

SETUP CONFIG

REGISTERS

FILTER CONFIG

REGISTERS

OFFSET REGISTERSGAIN REGISTERS*

SELECT PERIPHERAL

FUNCTIONS FOR

ADC CHANNEL

SELECT DIGITAL

FILTER TYPE

AND OUTPUT DATA RATE

DATA OUTPUT CODING

REFERENCE SOURCE

INPUT BUFFERS

SINC5 + SINC1

SINC3

SINC3 MAP

ENHANCED 50Hz AND 60Hz

GAIN CORRECTION

OPTIONALLY

PROGRAMMED

PER SETUP AS REQUIRED

(*FACTORY CALIBRATED)

OFFSET CORRECTION

OPTIONALLY PROGRAMMED

PER SETUP AS REQUIRED

0x20

0x21

0x22

0x23

0x28

0x29

0x2A

0x2B

0x38

0x39

0x3A

0x3B

0x30

0x31

0x32

0x33

SETUPCON3

SETUPCON0

SETUPCON2

SETUPCON1

FILTCON3

FILTCON0

FILTCON2

FILTCON1

GAIN3

GAIN0

GAIN2

GAIN1

OFFSET3

OFFSET0

OFFSET2

OFFSET1

12672-045

Figure 49. ADC Setup Register Grouping

Table 12. Setup Configuration Register 0

Reg.

Name

Bits

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

Reset

0x20 SETUPCON0

[15:8] Reserved BI_UNIPOLAR0

REFBUF0+ REFBUF0− AINBUF0+ AINBUF0− 0x1000 RW

[7:0] BURNOUT_EN0 Reserved REF_SEL0 Reserved

Table 13. Filter Configuration Register 0

Reg. Name Bits Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Reset RW

0x28 FILTCON0 [15:8] SINC3_MAP0 Reserved ENHFILTEN0

ENHFILT0 0x0500 RW

[7:0] Reserved ORDER0 ODR0

Table 14. Gain Register 0

Reg. Name Bits Bits[23:0] Reset RW

0x38 GAIN0 [23:0] GAIN0[23:0] 0x5XXXX0

Table 15. Offset Register 0

Reg. Name Bits Bits[23:0] Reset RW

0x30 OFFSET0 [23:0] OFFSET0[23:0] 0x800000 RW

Data Sheet AD7172-2

Rev. A | Page 25 of 60

Gain Registers

The gain registers are 24-bit registers that hold the gain

calibration coefficient for the ADC. The gain registers are

read/write registers. These registers are configured at power-on

with factory calibrated coefficients. Therefore, every device has

different default coefficients. The default value is automatically

overwritten if the user initiates a system full-scale calibration or

writes to a gain register. For more information on calibration,

see the Operating Modes section.

Offset Registers

The offset registers hold the offset calibration coefficient for the

ADC. The power-on reset value of the offset registers is 0x800000.

The offset registers are 24-bit read/write registers. The power-on

reset value is automatically overwritten if the user initiates an

internal or system zero-scale calibration or if the user writes to

an offset register.

ADC Mode and Interface Mode Configuration

The ADC mode register and the interface mode register configure

the core peripherals for use by the AD7172-2 and the mode for

the digital interface.

ADC Mode Register

The ADC mode register primarily sets the conversion mode of

the ADC to either continuous or single conversion. The user

can also select the standby and power-down modes, as well as

any of the calibration modes. In addition, this register contains

the clock source select bits and the internal reference enable

bits. The reference select bits are contained in the setup

configuration registers (see the ADC Setups section for more

information). The details of this register are shown in Table 16.

Interface Mode Register

The interface mode register configures the digital interface

operation. This register allows the user to control data-word length,

CRC enable, data plus status read, and continuous read mode. The

details of this register are shown in Table 17. For more information,

see the Digital Interface section.

Table 16. ADC Mode Register

Reg. Name Bits Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Reset RW

0x01 ADCMODE [15:8] REF_EN HIDE_DELAY SING_CYC Reserved Delay 0x0000 RW

[7:0] Reserved Mode CLOCKSEL Reserved

Table 17. Interface Mode Register

Reg. Name Bits Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Reset RW

0x02 IFMODE [15:8] Reserved ALT_SYNC IOSTRENGTH Reserved DOUT_RESET 0x0000 RW

[7:0] CONTREAD DATA_STAT REG_CHECK Reserved CRC_EN Reserved WL16

AD7172-2 Data Sheet

Rev. A | Page 26 of 60

Understanding Configuration Flexibility

The most straightforward implementation of the AD7172-2 is to

use two differential inputs with adjacent analog inputs and run

both of them with the same setup, gain correction, and offset

correction register. In this case, the user selects the following

differential inputs: AIN0/AIN1 and AIN2/AIN3. In Figure 50,

the registers shown in black font must be programmed for such

a configuration. The registers that are shown in gray font are

redundant in this configuration.

Programming the gain and offset registers is optional for any use

case, as indicated by the dashed lines between the register blocks.

An alternative way to implement these two fully differential

inputs is to take advantage of the four available setups.

Motivation for doing this includes having a different speed/noise

requirement on each of the differential inputs, or there may be a

specific offset or gain correction for each channel. Figure 51

shows how each of the differential inputs can use a separate

setup, allowing full flexibility in the configuration of each channel.

Figure 52 shows an example of how the channel registers span

between the analog input pins and the setup configurations down-

stream. In this example, one differential input and two single-ended

inputs are required. The single-ended inputs are the AIN2/AIN4

and AIN3/AIN4 combinations. The differential input pair is AIN0/

AIN1 and uses Setup 0. The two single-ended input pairs are set up

as diagnostics; therefore, they use a separate setup from the

differential input but share a setup between them, Setup 1. Given

that two setups are selected, SETUPCON0 and SETUPCON1

are programmed as required, and FILTCON0 and FILTCON1

are programmed as desired. Optional gain and offset correction

can be employed on a per setup basis by programming GAIN0 and

GAIN1 and OFFSET0 and OFFSET1.

In the example shown in Figure 52, the CH0 to CH2 registers

are used. Setting the MSB in each of these registers, the CH_EN0

to CH_EN2 bits enable the three combinations via the crosspoint

mux. When the AD7172-2 converts, the sequencer transitions in

ascending sequential order from CH0 to CH1 to CH2 before

looping back to CH0 to repeat the sequence.

SETUP CONFIG

REGISTERS

CHANNEL

REGISTERS FILTER CONFIG

REGISTERS OFFSET REGISTERSGAIN REGISTERS*

SELECT PERIPHERAL

FUNCTIONS FOR

ADC CHANNEL

SELECT ANALOG INPUT PAIRS

ENABLE THE CHANNEL

SELECT SETUP 0

SELECT DIGITAL

FILTER TYPE

AND OUTPUT DATA RATE

DATA OUTPUT CODING

REFERENCE SOURCE

INPUT BUFFERS

SINC5 + SINC1

SINC3

SINC3 MAP

ENHANCED 50Hz AND 60Hz

GAIN CORRECTION

OPTIONALLY

PROGRAMMED

PER SETUP AS REQUIRED

(*FACTORY CALIBRATED)

OFFSET CORRECTION

OPTIONALLY PROGRAMMED

PER SETUP AS REQUIRED

0x20

0x21

0x22

0x23

0x28

0x29

0x2A

0x2B

0x38

0x39

0x3A

0x3B

0x30

0x31

0x32

0x33

SETUPCON3

SETUPCON0

SETUPCON2

SETUPCON1

FILTCON3

FILTCON0

FILTCON2

FILTCON1

GAIN3

GAIN0

GAIN2

GAIN1

OFFSET3

OFFSET0

OFFSET2

OFFSET1

0x10

CH0

0x11

CH1

0x12

CH2

0x13

CH3

AIN0

AIN1

AIN2

AIN3

AIN4

12672-046

Figure 50. Two Fully Differential Inputs, Both Using a Single Setup (SETUPCON0; FILTCON0; GAIN0; OFFSET0)

SETUP CONFIG

REGISTERS

FILTER CONFIG

REGISTERS

OFFSET REGISTERSGAIN REGISTERS*

SELECT PERIPHERAL

FUNCTIONS FOR

ADC CHANNEL

SELECT DIGITAL

FILTER TYPE

AND OUTPUT DATA RATE

GAIN CORRECTION

OPTIONALLY

PROGRAMMED

PER SETUP AS REQUIRED

(*FACTORY CALIBRATED)

OFFSET CORRECTION

OPTIONALLY PROGRAMMED

PER SETUP AS REQUIRED

0x20

0x21

0x22

0x23

0x28

0x29

0x2A

0x2B

0x38

0x39

0x3A

0x3B

0x30

0x31

0x32

0x33

SETUPCON3

SETUPCON0

SETUPCON2

SETUPCON1

FILTCON3

FILTCON0

FILTCON2

FILTCON1

GAIN3

GAIN0

GAIN2

GAIN1

OFFSET3

OFFSET0

OFFSET2

OFFSET1

0x10

CH0

0x11

CH1

0x12

CH2

0x13

CH3

AIN0

AIN1

AIN2

AIN3

AIN4

CHANNEL

REGISTERS

DATA OUTPUT CODING

REFERENCE SOURCE

INPUT BUFFERS

SINC5 + SINC1

SINC3

SINC3 MAP

ENHANCED 50Hz AND 60Hz

12672-047

Figure 51. Two Fully Differential Inputs with a Setup per Channel

SETUP CONFIG

REGISTERS

FILTER CONFIG

REGISTERS

OFFSET REGISTERSGAIN REGISTERS*

SELECT PERIPHERAL

FUNCTIONS FOR

ADC CHANNEL

SELECT ANALOG INPUT PARTS

ENABLE THE CHANNEL

SELECT SETUP

SELECT DIGITAL

FILTER TYPE

AND OUTPUT DATA RATE

GAIN CORRECTION

OPTIONALLY

PROGRAMMED

PER SETUP AS REQUIRED

(*FACTORY CALIBRATED)

OFFSET CORRECTION

OPTIONALLY PROGRAMMED

PER SETUP AS REQUIRED

0x20

0x21

0x22

0x23

0x28

0x29

0x2A

0x2B

0x38

0x39

0x3A

0x3B

0x30

0x31

0x32

0x33

SETUPCON3

SETUPCON0

SETUPCON2

SETUPCON1

FILTCON3

FILTCON0

FILTCON2

FILTCON1

GAIN3

GAIN0

GAIN2

GAIN1

OFFSET3

OFFSET0

OFFSET2

OFFSET1

0x10

CH0

0x11

CH1

0x12

CH2

0x13

CH3

AIN0

AIN1

AIN2

AIN3

AIN4

CHANNEL

REGISTERS

DATA OUTPUT CODING

REFERENCE SOURCE

INPUT BUFFERS

SINC5 + SINC1

SINC3

SINC3 MAP

ENHANCED 50Hz AND 60Hz

12672-048

Figure 52. Mixed Differential and Single-Ended Configuration Using Multiple Shared Setups

AD7172-2 Data Sheet

Rev. A | Page 27 of 60

CIRCUIT DESCRIPTION

BUFFERED ANALOG INPUT

The AD7172-2 has true rail-to-rail, integrated, precision unity

gain buffers on both ADC analog inputs. The buffers provide

high input impedance with only 5 nA typical input current,

allowing high impedance sources connect directly to the analog

inputs. The buffers fully drive the internal ADC switch capacitor

sampling network, simplifying the analog front-end circuit

requirements while consuming a very efficient 0.38 mA typical

per buffer. Each analog input buffer amplifier is fully chopped,

meaning that it minimizes the offset error drift and 1/f noise of

the buffer. The 1/f noise profile of the ADC and buffer combined

is shown in Figure 53.

0.1 110 100 1k 10k

AMPLITUDE (dB)

FREQUENCY (Hz)

–250

–200

–150

–100

–50

12672-255

Figure 53. Shorted Input FFT (Analog Input Buffers Enabled)

The analog input buffers do not suffer from linearity degradation

when operating at the rails, unlike many discrete amplifiers. When

operating at or close to the AVDD1 and AVSS supply rails, there

is an increase in input current. This increase is most notable at

higher temperatures. Figure 40 and Figure 41 show the input

current for various conditions. With the analog input buffers

disabled, the average input current to the AD7172-2 changes

linearly with the differential input voltage at a rate of 6 µ A / V.

CROSSPOINT MULTIPLEXER

There are five analog input pins: AIN0, AIN1, AIN2, AIN3, and

AIN4. Each of these pins connects to the internal crosspoint

multiplexer. The crosspoint multiplexer enables any of these inputs

to be configured as an input pair, either single-ended or fully

differential. The AD7172-2 can have up to four active channels.

When more than one channel is enabled, the channels are

automatically sequenced in order from the lowest enabled channel

number to the highest enabled channel number. The output of

the multiplexer is connected to the input of the integrated true

rail-to-rail buffers. These buffers can be bypassed and the

multiplexer output can directly connect to the switched-capacitor

input of the ADC. The simplified analog input circuit is shown in

Figure 54.

AIN0

AIN1

AVDD1

AVSS

AVDD1

AVSS

AIN2

AVDD1

AIN4

AVDD1

AIN3

AVDD1

AVSS

Ø1

CS1

CS2

+IN

–IN

Ø2

Ø1

12672-056

Figure 54. Simplified Analog Input Circuit

The CS1 and CS2 capacitors have a magnitude in the order of a

number of picofarads each. This capacitance is the combination

of both the sampling capacitance and the parasitic capacitance.

Fully Differential Inputs

Because the AIN0 to AIN4 analog inputs are connected to a

crosspoint multiplexer, any combination of signals can create an

analog input pair. This allows the user to select two fully

differential inputs or four single-ended inputs.

If two fully differential input paths are connected to the AD7172-2,

using AIN0/AIN1 as one differential input pair and AIN2/AIN3

as the second differential input pair is recommended. This is

due to the relative locations of these pins to each other. Decouple all

analog inputs to AVSS.

Single-Ended Inputs

The user can also choose to measure four different single-ended

analog inputs. In this case, each of the analog inputs is converted

as the difference between the single-ended input to be measured

and a set analog input common pin. Because there is a crosspoint

multiplexer, the user can set any of the analog inputs as the

common pin. An example of such a scenario is to connect the

AIN4 pin to AVSS or to the REFOUT voltage (that is, AVSS +

2.5 V) and select this input when configuring the crosspoint multi-

plexer. When using the AD7172-2 with single-ended inputs, the

INL specification is degraded.

AD7172-2 Data Sheet

Rev. A | Page 28 of 60

AD7172-2 REFERENCE

The AD7172-2 offers the user the option of either supplying an

external reference to the REF+ and REF− pins of the device or

allowing the use of the internal 2.5 V, low noise, low drift reference.

Select the reference source to be used by the analog input by setting

the REF_SELx bits (Bits[5:4]) in the setup configuration registers

appropriately. The structure of the Setup Configuration 0 register

is shown in Table 18. The AD7172-2 defaults on power-up to

use the external reference inputs, REF+ and REF−.

External Reference

The AD7172-2 has a fully differential reference input applied

through the REF+ and REF− pins. Standard low noise, low drift

voltage references, such as the ADR445, ADR444, and ADR441,

are recommended for use. Apply the external reference to the

AD7172-2 reference pins as shown in Figure 55. Decouple the

output of any external reference to AVSS. As shown in Figure 55,

the ADR445 output is decoupled with a 0.1 µF capacitor at the

output for stability purposes. The output is then connected to a

4.7 µF capacitor, which acts as a reservoir for any dynamic charge

required by the ADC, and followed by a 0.1 µF decoupling

capacitor at the REF+ input. This capacitor is placed as close

as possible to the REF+ and REF− pins.

The REF− pin is connected directly to the AVSS potential. On

power-up of the AD7172-2, the internal reference is disabled by

default. The external reference is used by default instead of the

internal reference. When an external reference is used instead of

the internal reference to supply the AD7172-2, attention must be

paid to the output of the REFOUT pin. If the internal reference

is not being used elsewhere in the application, ensure that the

REFOUT pin is not hardwired to AVSS because this draws a

large current on power-up. The internal reference is controlled

by the REF_EN bit (Bit 15) in the ADC mode register, which is

shown in Table 19.

Internal Reference

The AD7172-2 includes a low noise, low drift voltage reference.

The internal reference has a 2.5 V output. The internal reference is

output on the REFOUT pin after the REF_EN bit in the ADC

mode register is set and is decoupled to AVSS with a 0.1 µF

capacitor. The AD7172-2 internal reference is disabled by

default on power-up.

The REFOUT signal is buffered before being output to the pin.

The signal can be used externally in the circuit as a common-mode

source for external amplifier configurations.

REF–

REF+

4.7µF0.1µF

11 1

0.1µF

3V TO 18V

ADR441

5V VREF

AD7172-2

ALL DECOUPLING IS TO AVSS.

ANY OF THE ADR44x FAMILY OF REFERENCES CAN BE USED.

THE ADR441 ENABLES REUSE OF THE 3.3V ANALOG SUPPLY

NEEDED FOR AVDD1 TO POWER THE REFERENCE V

12672-159

Figure 55. External Reference (ADR441) Connected to AD7172-2 Reference Pins

Table 18. Setup Configuration 0 Register

Reg. Name Bits Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Reset RW

0x20

SETUPCON0

[15:8]

Reserved

BI_UNIPOLAR0

REFBUF0+

REFBUF0−

AINBUF0+

AINBUF0−

0x1000 RW

[7:0] BURNOUT_EN0

Reserved REF_SEL0 Reserved

Table 19. ADC Mode Register

Reg. Name Bits Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 Reset RW

0x01 ADCMODE [15:8] REF_EN HIDE_DELAY SING_CYC Reserved Delay 0x0000 RW

[7:0] Reserved Mode CLOCKSEL Reserved

Data Sheet AD7172-2

Rev. A | Page 29 of 60

BUFFERED REFERENCE INPUT

The AD7172-2 has true rail-to-rail, integrated, precision unity-

gain buffers on both ADC reference inputs. The buffers provide

the benefit of providing high input impedance and allowing

high impedance external sources to be directly connected to the

reference inputs. The integrated reference buffers can fully drive

the internal reference switch capacitor sampling network,

simplifying the reference circuit requirements while consuming

a very efficient 0.38 mA typical per buffer. Each reference input

buffer amplifier is fully chopped, meaning that it minimizes the

offset error drift and 1/f noise of the buffer. When using an

external reference, such as the ADR445, ADR444, or ADR441,

these buffers are not required because these references, with

proper decoupling, can drive the reference inputs directly.

CLOCK SOURCE

The AD7172-2 uses a nominal master clock of 2 MHz. The

AD7172-2 can source the sampling clock from one of three

sources:

• Internal oscillator

• External crystal (use a 16 MHz crystal, automatically

divided internally to set the 2 MHz clock)

• External clock source

All output data rates listed in the data sheet relate to a master

clock rate of 2 MHz. Using a lower clock frequency from, for

instance, an external source scales any listed data rate

proportionally. To achieve the specified data rates, particularly

rates for rejection of 50 Hz and 60 Hz, use a 2 MHz clock. The

source of the master clock is selected by setting the CLOCKSEL bits

(Bits[3:2]) in the ADC mode register as shown in Table 19. The

default operation on power-up and reset of the AD7172-2 is to

operate with the internal oscillator. It is possible to fine tune the

output data rate and filter notch at low output data rates using

the SINC3_MAPx bit (Bit 7 of the FILTCONx registers). See the

Sinc3 Filter section for more information.

Internal Oscillator

The internal oscillator runs at 16 MHz, is internally divided

down to 2 MHz for the modulator, and can be used as the ADC

master clock. The internal oscillator is the default clock source for

the AD7172-2 and is specified with an accuracy of ±2.5%.

There is an option to allow the internal clock oscillator to be

output on the XTAL2/CLKIO pin. The clock output is driven to

the IOVDD logic level. Use of this option can affect the dc

performance of the AD7172-2 due to the disturbance

introduced by the output driver. The extent to which the

performance is affected depends on the IOVDD voltage supply.

Higher IOVDD voltages create a wider logic output swing from

the driver and affect performance to a greater extent. This effect

is further exaggerated if the IOSTRENGTH bit is set at higher

IOVDD levels (see Table 29 for more information).

External Crystal

If higher precision, lower jitter clock sources are required, the

AD7172-2 can use an external crystal to generate the master clock.

The crystal is connected to the XTAL1 and XTAL2/CLKIO pins. A

recommended crystal for use is the FA-20H, a 16 MHz, 10 ppm,

9 pF crystal from Epson-Toyocom that is available in a surface-

mount package. As shown in Figure 56, insert two capacitors

from the traces connecting the crystal to the XTAL1 and XTAL2/

CLKIO pins. These capacitors allow circuit tuning. Connect

these capacitors to the DGND pin. The value for these capacitors

depends on the length and capacitance of the trace connections

between the crystal and the XTAL1 and XTAL2/CLKIO pins.

Therefore, the values of these capacitors differ depending on the

printed circuit board (PCB) layout and the crystal employed.

CX1

CX2

XTAL1

XTAL2/CLKIO

1DECOUPLE TO DGND.

AD7172-2

12672-160

Figure 56. External Crystal Connections

The external crystal circuitry can be sensitive to the SCLK

edges, depending on SCLK frequency, IOVDD voltage, crystal

circuitry layout, and the crystal used. During crystal startup, any

disturbances caused by the SLCK edges can cause double edges

on the crystal input, resulting in invalid conversions until the

crystal voltage has reached a high enough level such that any

interference from the SCLK edges is insufficient to cause double

clocking. This double clocking can be avoided by ensuring that

the crystal circuitry has reached a sufficient voltage level after

startup before applying any SCLK.

Due to the nature of the crystal circuitry, it is recommended

that empirical testing of the circuit be performed under the

required conditions, with the final PCB layout and crystal, to

ensure correct operation.

External Clock

The AD7172-2 can also use an externally supplied clock. In

systems where this is desirable, the external clock is routed to

the XTAL2/CLKIO pin. In this configuration, the XTAL2/

CLKIO pin accepts the externally sourced clock and routes it to

the modulator. The logic level of this clock input is defined by

the voltage applied to the IOVDD pin.

AD7172-2 Data Sheet

Rev. A | Page 30 of 60

DIGITAL FILTERS

The AD7172-2 has three flexible filter options to allow

optimization of noise, settling time, and rejection:

• Sinc5 + sinc1 filter

• Sinc3 filter

• Enhanced 50 Hz and 60 Hz rejection filters

SINC1

SINC5

SINC3

50Hz AND 60Hz

POSTFILTER

12672-058

Figure 57. Digital Filter Block Diagram

The filter and output data rate are configured by setting the

appropriate bits in the filter configuration register for the

selected setup. Each channel can use a different setup and,

therefore, a different filter and output data rate. See the Register

Details section for more information.

SINC5 + SINC1 FILTER

The sinc5 + sinc1 filter is targeted at multiplexed applications

and achieves single cycle settling at output data rates of 2.6 kSPS

and less. The sinc5 block output is fixed at the maximum rate of

31.25 kSPS, and the sinc1 block output data rate can be varied to

control the final ADC output data rate. Figure 58 shows the

frequency domain response of the sinc5 + sinc1 filter at a 50 SPS

output data rate. The sinc5 + sinc1 filter has a slow roll-off over

frequency and narrow notches.

–120

015010050

FILTER GAIN (dB)

FREQUENCY (Hz)

–100

–80

–60

–40

–20

12672-059

Figure 58. Sinc5 + Sinc1 Filter Response at 50 SPS ODR

The output data rates with the accompanying settling time and

rms noise for the sinc5 + sinc1 filter are shown in Table 20 and

Table 21.

SINC3 FILTER

The sinc3 filter achieves the best single-channel noise performance

at lower rates and is, therefore, most suitable for single-channel

applications. The sinc3 filter always has a settling time equal to

tSETTLE = 3/Output Data Rate

Figure 59 shows the frequency domain filter response for the

sinc3 filter. The sinc3 filter has good roll-off over frequency and

has wide notches for good notch frequency rejection.

–120

0150

10050

FILTER GAIN (dB)

FREQUENCY(Hz)

–100

–80

–60

–40

–20

–110

–90

–70

–50

–30

–10

12672-060

Figure 59. Sinc3 Filter Response

The output data rates with the accompanying settling time and

rms noise for the sinc3 filter are shown in Table 22 and Table 2 3. It

is possible to fine tune the output data rate for the sinc3 filter by

setting the SINC3_MAPx bit in the filter configuration registers.

If this bit is set, the mapping of the filter register changes to directly

program the decimation rate of the sinc3 filter. All other options

are eliminated. The data rate when on a single channel can be

calculated using the following equation:

4:0]FILTCONx[1

RateDataOutput

MOD

=32

where:

fMOD is the modulator rate (MCLK/2) and is equal to 1 MHz.

FILTCONx[14:0] are the contents on the filter configuration

registers excluding the MSB.

For example, an output data rate of 50 SPS can be achieved with

SINC3_MAPx enabled by setting the FILTCONx[14:0] bits to a

value of 625.

Data Sheet AD7172-2

Rev. A | Page 31 of 60

SINGLE CYCLE SETTLING

The AD7172-2 can be configured by setting the SING_CYC bit

in the ADC mode register so that only fully settled data is output,

thus effectively putting the ADC into a single cycle settling mode.

This mode achieves single cycle settling by reducing the output

data rate to be equal to the settling time of the ADC for the selected

output data rate. This bit has no effect with the sinc5 + sinc1

filter at output data rates of 2.6 kSPS and less.

Figure 60 shows a step on the analog input with single cycle

settling mode disabled and the sinc3 filter selected. The analog

input requires at least three cycles after the step change for the

output to reach the final settled value.

1/ODR

ANALOG

INPUT

FULLY

SETTLED

ADC

OUTPUT

12672-061

Figure 60. Step Input Without Single Cycle Settling

Figure 61 shows the same step on the analog input but with

single cycle settling enabled. The analog input requires at least a

single cycle for the output to be fully settled. The output data

rate, as indicated by the RDY signal, is now reduced to equal the

settling time of the filter at the selected output data rate.

tSETTLE

ANALOG

INPUT

FULLY

SETTLED

ADC

OUTPUT

12672-062

Figure 61. Step Input with Single Cycle Settling

Table 20. Output Data Rate, Settling Time, and Noise Using the Sinc5 + Sinc1 Filter with Input Buffers Disabled

Default Output

Data Rate (SPS);

SING_CYC = 0 and

Single Channel

Enabled1

Output Data Rate

(SPS/Channel);

SING_CYC = 1 or with

Multiple Channels

Enabled1

Settling

Time1

Notch

Frequency

(Hz)

Noise

(µV rms)

Effective

Resolution with

5 V Reference

(Bits)

Noise

(µV p-p)2

Peak-to-Peak

Resolution with

5 V Reference

(Bits)

31,250 6211 161 µs 31,250 8.2 20.2 66 17.2

15,625

5181

193 µs

15,625 7.0 20.4

17.5

10,417 4444 225 µs 10,417 6.0 20.7 45 17.8

5208 3115 321 µs 5208 4.5 21.1 33 18.2

2597 2597 385 µs 3906 3.9 21.3 29 18.4

1007 1007 993 µs 1157 2.2 22.2 15 19.3

503.8 503.8 1.99 ms 539 1.5 22.6 10 19.9

381 381 2.63 ms 401 1.3 22.9 9.1 20.1

200.3 200.3 4.99 ms 206 0.88 23.3 6.1 20.6

100.2 100.2 9.99 ms 102 0.64 23.8 4.2 21.2

59.52 59.52 16.8 ms 59.98 0.48 24 3.2 21.6

49.68 49.68 20.13 ms 50 0.47 24 3.1 21.6

20.01 20.01 49.98 ms 20 0.27 24 1.7 22.4

16.63 16.63 60.13 ms 16.67 0.25 24 1.6 22.6

10 10 100 ms 10 0.2 24 1.1 23.1

5 5 200 ms 5 0.14 24 0.75 24

2.5 2.5 400 ms 2.5 0.091 24 0.32 24

1.25 1.25 800 ms 1.25 0.088 24 0.32 24

1 The settling time is rounded to the nearest microsecond. This is reflected in the output data rate and channel switching rate. Channel switching rate = 1 ÷ settling time.

2 1000 samples.

AD7172-2 Data Sheet

Rev. A | Page 32 of 60

Table 21. Output Data Rate, Settling Time, and Noise Using the Sinc5 + Sinc1 Filter with Input Buffers Enabled

Default Output Data

Rate (SPS);

SING_CYC = 0 and

Single Channel

Enabled1

Output Data Rate

(SPS/Channel);

SING_CYC = 1 or

with Multiple

Channels Enabled1

Settling

Time1

Notch

Frequency

(Hz)

Noise

(µV rms)

Effective

Resolution with

5 V Reference

(Bits)

Noise

(µV p-p)2

Peak-to-Peak

Resolution with

5 V Reference

(Bits)

31,250 6211 161 µs 31,250 9.5 20 74 17

15,625

5181

193 µs

15,625 8.2 20.2 63 17.3

10,417 4444 225 µs 10,417 7.1 20.4 53 17.5

5208 3115 321 µs 5208 5.3 20.9 39 18

2597 2597 385 µs 3906 4.7 21 29 18.4

1007 1007 993 µs 1157 2.6 21.9 16 19.3

503.8 503.8 1.99 ms 539 1.8 22.4 12 19.7

381

381 2.63 ms 401 1.6 22.6 11 19.8

200.3 200.3 4.99 ms 206 1.1 23.1 7.5 20.3

100.2 100.2 9.99 ms 102 0.75 23.6 5.1 21

59.52 59.52 16.8 ms 59.98 0.62 24 3.6 21.4

49.68 49.68 20.13 ms 50 0.53 24 3.3 21.5

20.01 20.01 49.98 ms 20 0.32 24 1.8 22.4

16.63 16.63 60.13 ms 16.67 0.32 24 1.7 22.5

10 10 100 ms 10 0.25 24 1.2 23

5 5 200 ms 5 0.18 24 0.83 23.5

2.5 2.5 400 ms 2.5 0.11 24 0.35 24

1.25 1.25 800 ms 1.25 0.089 24 0.35 24

1 The settling time is rounded to the nearest microsecond. This is reflected in the output data rate and channel switching rate. Channel switching rate = 1 ÷ settling time.

2 1000 samples.

Data Sheet AD7172-2

Rev. A | Page 33 of 60

Table 22. Output Data Rate, Settling Time, and Noise Using the Sinc3 Filter with Input Buffers Disabled

Default Output

Data Rate (SPS);

SING_CYC = 0 and

Single Channel

Enabled1

Output Data Rate

(SPS/Channel);

SING_CYC = 1 or with

Multiple Channels

Enabled1

Settling

Time1

Notch

Frequency

(Hz)

Noise

(µV rms)

Effective

Resolution with

5 V Reference

(Bits)

Noise

(µV p-p)2

Peak-to-Peak

Resolution with

5 V Reference

(Bits)

31,250 10,309 97 µs 31,250 211 15.5 1600 12.5

15,625 5,181 193 µs 15,625 27.2 18.5 205 15.6

10,417 3,460 289 µs 10,417 7.9 20.3 57 17.4

5,208 1,733 577 µs 5,208 3.7 21.4 27 18.5

2,604 867.3 1.15 ms 2,604 2.5 21.9 17 19.2

1,008 335.9 2.98 ms 1,008 1.6 22.6 11 19.8

504 167.98 5.95 ms 504 1.1 23.1 7.5 20.3

400.6 133.5 7.49 ms 400.6 0.99 23.3 6.7 20.5

200.3 66.67 14.98 ms 200.3 0.68 23.7 4.6 21

100.2 33.39 29.95 ms 100.2 0.47 24 3.1 21.6

59.98 19.99 50.02 ms 59.98 0.38 24 2.5 21.9

50 16.67 60 ms 50 0.35 24 2.3 22

20.01 6.67 149.95 ms 20.01 0.21 24 1.2 23

16.67

5.56

180 ms

16.67

0.21

1.1

23.1

10 3.33 300 ms 10 0.18 24 0.83 23.5

5 1.67 600 ms 5 0.18 24 0.56 24

2.5 0.83 1.2 sec 2.5 0.16 24 0.41 24

1.25 0.42 2.4 sec 1.25 0.054 24 0.27 24

1 The settling time is rounded to the nearest microsecond. This is reflected in the output data rate and channel switching rate. Channel switching rate = 1 ÷ settling time.

2 1000 samples.

Table 23. Output Data Rate, Settling Time, and Noise Using the Sinc3 Filter with Input Buffers Enabled

Default Output

Data Rate (SPS);

SING_CYC = 0 and

Single Channel

Enabled1

Output Data Rate

(SPS/Channel);

SING_CYC = 1 or with

Multiple Channels

Enabled1

Settling

Time1

Notch

Frequency

(Hz)

Noise

(µV rms)

Effective

Resolution with

5 V Reference

(Bits)

Noise

(µV p-p)2

Peak-to-Peak

Resolution with

5 V Reference

(Bits)

31,250 10,309 97 µs 31,250 212 15.5 1600 12.5

15,625 5,181 193 µs 15,625 27.7 18.5 210 15.5

10,417 3,460 289 µs 10,417 8.5 20.2 63 17.3

5,208

1,733 577

µs

5,208

4.3 21.2 28 18.4

2,604 867.3 1.15 ms 2,604 3.0 21.7 20 19

1,008 335.9 2.98 ms 1,008 1.8 22.4 13 19.6

504 167.98 5.95 ms 504 1.3 22.9 8.9 20.1

400.6

133.5

7.49 ms

400.6

1.2

8.2

20.2

200.3 66.67 14.98 ms 200.3 0.82 23.5 5.6 20.8

100.2 33.39 29.95 ms 100.2 0.57 24 3.8 21.3

59.98 19.99 50.02 ms 59.98 0.45 24 2.8 21.8

50 16.67 60 ms 50 0.44 24 2.5 22

20.01 6.67 149.95 ms 20.01 0.26 24 1.3 22.9

16.67 5.56 180 ms 16.67 0.24 24 1.2 23

10 3.33 300 ms 10 0.19 24 0.91 23.4

5 1.67 600 ms 5 0.12 24 0.62 24

2.5 0.83 1.2 sec 2.5 0.098 24 0.45 24

1.25

0.42

2.4 sec

1.25

0.073

0.29

1 The settling time is rounded to the nearest microsecond. This is reflected in the output data rate and channel switching rate. Channel switching rate = 1 ÷ settling time.

2 1000 samples.

AD7172-2 Data Sheet

Rev. A | Page 34 of 60

ENHANCED 50 Hz AND 60 Hz REJECTION FILTERS

The enhanced filters provide rejection of 50 Hz and 60 Hz

simultaneously and allow the user to trade off settling time and

rejection. These filters can operate up to 27.27 SPS or can reject

up to 90 dB of 50 Hz ± 1 Hz and 60 Hz ± 1 Hz interference.

These filters are realized operated by postfiltering the output of the

sinc5 + sinc1 filter. For this reason, the sinc5 + sinc1 filter must

be selected when using the enhanced filters to achieve the

specified settling time and noise performance. Table 24 shows the

output data rates with the accompanying settling time,

rejection, and rms noise. Figure 62 to Figure 69 show the

frequency domain plots of the responses from the enhanced filters.

Table 24. Enhanced Filters Output Data Rate, Noise, Settling Time, and Rejection Using the Enhanced Filters

Output Data Rate (SPS)

Settling

Time (ms)

Simultaneous Rejection of

50 Hz ± 1 Hz and 60 Hz ± 1 Hz (dB)1

Noise

(µV rms)

Peak-to-Peak

Resolution (Bits) Comments

27.27 36.67 47 0.45 21.4 See Figure 62 and Figure 65

40.0

0.44

21.4

See Figure 63 and Figure 66

20 50.0 85 0.41 21.7 See Figure 64 and Figure 67

16.667 60.0 90 0.417 21.7 See Figure 68 and Figure 69

1 Master clock = 2.00 MHz.

Data Sheet AD7172-2

Rev. A | Page 35 of 60

–100

0600

FILTER GAIN (dB)

FREQUENCY (Hz)

–90

–80

–70

–60

–50

–40

–30

–20

–10

100 200 300 400 500

12672-063

Figure 62. 27.27 SPS ODR, 36.67 ms Settling Time

–100

FILTER GAIN (dB)

FREQUENCY (Hz)

–90

–80

–70

–60

–50

–40

–30

–20

–10

600

100 200 300 400 500

12672-065

Figure 63. 25 SPS ODR, 40 ms Settling Time

–100

0600

FILTER GAIN (dB)

FREQUENCY (Hz)

–90

–80

–70

–60

–50

–40

–30

–20

–10

100 200 300 400 500

12672-067

Figure 64. 20 SPS ODR, 50 ms Settling Time

–100

40 70

FILTER GAIN (dB)

FREQUENCY (Hz)

–90

–80

–70

–60

–50

–40

–30

–20

–10

45 50 55 60 65

12672-064

Figure 65. 27.27 SPS ODR, 36.67 ms Settling Time (40 – 70 Hz)

–100

40 70

FILTER GAIN (dB)

FREQUENCY (Hz)

–90

–80

–70

–60

–50

–40

–30

–20

–10

45 50 55 60 65

12672-066

Figure 66. 25 SPS ODR, 40 ms Settling Time (40 – 70 Hz)

–100

40 70

FILTER GAIN (dB)

FREQUENCY (Hz)

–90

–80

–70

–60

–50

–40

–30

–20

–10

45 50 55 60 65

12672-068

Figure 67. 20 SPS ODR, 50 ms Settling Time (40 – 70 Hz)

AD7172-2 Data Sheet

Rev. A | Page 36 of 60

–100

0600

FILTER GAIN (dB)

FREQUENCY (Hz)

–90

–80

–70

–60

–50

–40

–30

–20

–10

100 200 300 400 500

12672-069

Figure 68. 16.667 SPS ODR, 60 ms Settling Time

–100

40 70

FILTER GAIN (dB)

FREQUENCY (Hz)

–90

–80

–70

–60

–50

–40

–30

–20

–10

45 50 55 60 65

12672-070

Figure 69. 16.667 SPS ODR, 60 ms Settling Time (40 – 70 Hz)

Data Sheet AD7172-2

Rev. A | Page 37 of 60

OPERATING MODES

The AD7172-2 has a number of operating modes that can be set

from the ADC mode register and interface mode register (see

Table 28 and Table 29). These modes are as follows and are

described in the following sections:

• Continuous conversion mode

• Continuous read mode

• Single conversion mode

• Standby mode

• Power-down mode

• Calibration modes (three)

CONTINUOUS CONVERSION MODE

Continuous conversion is the default power-up mode. The

AD7172-2 converts continuously, and the RDY bit in the status

the RDY output also goes low when a conversion is complete. To

read a conversion, the user writes to the communications register,

indicating that the next operation is a read of the data register.

When the data-word has been read from the data register, the

DOUT/RDY pin goes high.

The user can read this register additional times, if required.

However, the user must ensure that the data register is not being

accessed at the completion of the next conversion; otherwise,

the new conversion word is lost.

When several channels are enabled, the ADC automatically

sequences through the enabled channels, performing one

conversion on each channel. When all the channels have been

converted, the sequence starts again with the first channel. The

channels are converted in order from the lowest enabled

channel to the highest enabled channel. The data register is

updated as soon as each conversion is available. The RDY

output pulses low each time a conversion is available. The user

can then read the conversion while the ADC converts the next

enabled channel.

If the DATA_STAT bit in the interface mode register is set to 1,

the contents of the status register, along with the conversion data,

are output each time the data register is read. The status register

indicates the channel to which the conversion corresponds.

DIN

SCLK

DOUT/RDY

0x44 0x44

DATA DATA

12672-071

Figure 70. Continuous Conversion Mode

AD7172-2 Data Sheet

Rev. A | Page 38 of 60

CONTINUOUS READ MODE

In continuous read mode, it is not required to write to the

communications register before reading ADC data; apply only

the required number of SCLKs after the RDY output goes low to

indicate the end of a conversion. When the conversion is read,

the RDY output returns high until the next conversion is

available. In this mode, the data can be read only once. The user

must also ensure that the data-word is read before the next

conversion is complete. If the user has not read the conversion

before the completion of the next conversion or if insufficient

serial clocks are applied to the AD7172-2 to read the data-word,

the serial output register is reset shortly before the next

conversion is complete, and the new conversion is placed in the

output serial register. The ADC must be configured for

continuous conversion mode to use continuous read mode.

To enable continuous read mode, set the CONTREAD bit in the

interface mode register. When this bit is set, the only serial interface

operations possible are reads from the data register. To exit con-

tinuous read mode, issue a dummy read of the ADC data register

command (0x44) while the RDY output is low. Alternatively, apply

a software reset, that is, 64 SCLKs with CS = 0 and DIN = 1.

This resets the ADC and all register contents. These are the only

commands that the interface recognizes after it is placed in

continuous read mode. Hold DIN low in continuous read mode

until an instruction is to be written to the device.

If multiple ADC channels are enabled, each channel is output

in turn, with the status bits being appended to the data if the

DATA_STAT bit is set in the interface mode register. The status

DIN

SCLK

DOUT/RDY

0x02

DATA DATA DATA

0x0080

12672-072

Figure 71. Continuous Read Mode

Data Sheet AD7172-2

Rev. A | Page 39 of 60

SINGLE CONVERSION MODE

In single conversion mode, the AD7172-2 performs a single

conversion and is placed in standby mode after the conversion

is complete. The RDY output goes low to indicate the completion

of a conversion. When the data-word has been read from the data

several times, if required, even when the RDY output has

gone high.

If several channels are enabled, the ADC automatically

sequences through the enabled channels and performs a

conversion on each channel. When a conversion is started, the

RDY output goes high and remains high until a valid conversion is

available and CS is low.

When the conversion is available, the RDY output goes low. The

ADC then selects the next channel and begins a conversion. The

user can read the present conversion while the next conversion is

being performed. When the next conversion is complete, the data

which to read the conversion. When the ADC has performed a

single conversion on each of the selected channels, it returns to

standby mode.

If the DATA_STAT bit in the interface mode register is set to 1,

the contents of the status register, along with the conversion, are

output each time the data register is read. The two LSBs of the

status register indicate the channel to which the conversion

corresponds.

DIN

SCLK

DOUT/RDY

0x01 0x44

DATA

0x8010

12672-073

Figure 72. Single Conversion Mode

AD7172-2 Data Sheet

Rev. A | Page 40 of 60

STANDBY AND POWER-DOWN MODES

In standby mode, most blocks are powered down. The LDO

regulators remain active so that the registers maintain their

contents. The internal reference remains active if enabled, and

the crystal oscillator remains active if selected. To power down

the reference in standby mode, set the REF_EN bit in the ADC

mode register to 0. To power down the clock in standby mode,

set the CLOCKSEL bits in the ADC mode register to 00

(internal oscillator).

In power-down mode, all blocks are powered down, including

the LDO regulators. All registers lose their contents, and the GPIO

outputs are placed in three-state. To prevent accidental entry to

power-down mode, the ADC must first be placed in standby

mode. Exiting power-down mode requires 64 SCLKs with CS = 0

and DIN = 1, that is, a serial interface reset. A delay of 500 µs is

recommended before issuing a subsequent serial interface

command to allow the LDO regulator to power up.

CALIBRATION

The AD7172-2 allows a two-point calibration to be performed

to eliminate any offset and gain errors. Three calibration modes

eliminate these offset and gain errors on a per setup basis:

• Internal zero-scale calibration mode

• System zero-scale calibration mode

• System full-scale calibration mode

There is no internal full-scale calibration mode because this is

calibrated in the factory at the time of production.

Only one channel can be active during calibration. After each

conversion, the ADC conversion result is scaled using the ADC

calibration registers before being written to the data register.

The default value of the offset register is 0x800000, and the

nominal value of the gain register is 0x555555. The calibration

range of the ADC gain is from 0.4 × VREF to 1.05 × VREF. The

following equations show the calculations that are used. In

unipolar mode, the ideal relationship—that is, not taking into

account the ADC gain error and offset error—is as follows:

400000x0

800000)x0(2

75.0

××











−−×

=Gain

Offset

Data

REF

In bipolar mode, the ideal relationship—that is, not taking into

account the ADC gain error and offset error—is as follows:

( )

800000x0

400000x0

800000

x0––2

75.

+×











×

=Gain

Offset

Data

REF

To start a calibration, write the relevant value to the mode bits

(Bits[6:4]) in the ADC mode register. The DOUT/RDY pin and

the RDY bit (Bit 7) in the status register go high when the

calibration initiates. When the calibration is complete, the contents

of the corresponding offset or gain register are updated, the RDY

bit in the status register is reset, the RDY output pin returns low

(if CS is low), and the AD7172-2 reverts to standby mode.

During an internal offset calibration, the selected positive

analog input pin is disconnected, and both modulator inputs

are connected internally to the selected negative analog input

pin. Therefore, it is necessary to ensure that the voltage on the

selected negative analog input pin does not exceed the allowed

limits and is free from excessive noise and interference.

However, for system calibrations, the system zero-scale (offset)

and system full-scale (gain) voltages must be applied to the

ADC pins before initiating the calibration modes. As a result,

errors external to the ADC are removed.

From an operational point of view, treat a calibration like

another ADC conversion. An offset calibration, if required,

must always be performed before a full-scale calibration. Set the

system software to monitor the RDY bit in the status register or

the RDY output to determine the end of a calibration via a

polling sequence or an interrupt-driven routine. All calibrations

require a time equal to the settling time of the selected filter and

output data rate to be completed.

An internal offset calibration, system zero-scale calibration, and

system full-scale calibration can be performed at any output data

rate. Using lower output data rates results in better calibration

accuracy and is accurate for all output data rates. A new offset

calibration is required for a given channel if the reference source

for that channel is changed.

The offset error is typically ±40 µV, and an offset calibration

reduces the offset error to the order of the noise. The gain error

is factory calibrated at ambient temperature. Following this

calibration, the gain error is typically ±35 ppm of FSR.

The AD7172-2 provides the user with access to the on-chip

calibration registers, allowing the microprocessor to read the

calibration coefficients of the device and to write calibration

coefficients. A read or write of the offset and gain registers can

be performed at any time except during an internal or self

calibration.

Data Sheet AD7172-2

Rev. A | Page 41 of 60

DIGITAL INTERFACE

The programmable functions of the AD7172-2 are controlled via

the SPI. The serial interface of the AD7172-2 consists of four

signals: CS, DIN, SCLK, and DOUT/RDY. The DIN input

transfers data into the on-chip registers, and the DOUT output

accesses data from the on-chip registers. SCLK is the serial clock

input for the device, and all data transfers (either on DIN input or

on DOUT output) occur with respect to the SCLK signal.

The DOUT/RDY pin also functions as a data ready signal, with

the output going low if CS is low when a new data-word is available

in the data register. The RDY output is reset high when a read

operation from the data register is complete. The RDY output

also goes high before updating the data register to indicate when

not to read from the device to ensure that a data read is not

attempted while the register is being updated. Take care to avoid

reading from the data register when the RDY output is about to

go low. The best method to ensure that no data read occurs is to

always monitor the RDY output; start reading the data register as

soon as the RDY output goes low; and ensure a sufficient SCLK

rate, such that the read is completed before the next conversion

result. CS selects a device. CS can decode the AD7172-2 in systems

where several components are connected to the serial bus.

Figure 2 and Figure 3 show timing diagrams for interfacing to

the AD7172-2 using CS to decode the device. Figure 2 shows the

timing for a read operation from the AD7172-2, and Figure 3

shows the timing for a write operation to the AD7172-2. It is

possible to read from the data register several times even though

the RDY output returns high after the first read operation.

However, ensure that the read operations are completed before the

next output update occurs. In continuous read mode, the data

The serial interface can operate in 3-wire mode by tying CS low.

In this case, the SCLK, DIN, and DOUT/RDY pins communicate

with the AD7172-2. The end of the conversion can also be

monitored using the RDY bit in the status register.

The AD7172-2 can be reset by writing 64 SCLKs with CS = 0

and DIN = 1. A reset returns the interface to the state in which it

expects a write to the communications register. This operation

resets the contents of all registers to their power-on values.

Following a reset, allow a period of 500 µs before addressing the

serial interface.

CHECKSUM PROTECTION

The AD7172-2 has a checksum mode that can improve interface

robustness. Using the checksum ensures that only valid data is

written to a register and allows data read from a register to be

validated. If an error occurs during a register write, the

CRC_ERROR bit is set in the status register. However, to ensure

that the register write was successful, read back the register and

verify the checksum.

For CRC checksum calculations during a write operation, the

following polynomial is always used:

x8 + x2 + x + 1

During read operations, the user can select between this

polynomial and a simpler exclusive or (XOR) function. The

XOR function requires less time to process on the host

microcontroller than the polynomial-based checksum. The

CRC_EN bits in the interface mode register enable and disable

the checksum and allow the user to select between the

polynomial check and the simple XOR check.

The checksum is appended to the end of each read and write

transaction. The checksum calculation for the write transaction

is calculated using the 8-bit command word and the 8-bit to

24-bit data. For a read transaction, the checksum is calculated

using the command word and the 8-bit to 32-bit data output.

Figure 73 and Figure 74 show SPI write and read transactions,

respectively.

8-BIT COMMAND 8-BIT CRCUP TO 24-BIT INPUT

CS DATA CRC

DIN

SCLK

12672-074

Figure 73. SPI Write Transaction with CRC

8-BIT COMMAND 8-BIT CRC

UP TO 32-BIT

OUTPUT

CMD

DATA CRC

DIN

SCLK

DOUT/

RDY

12672-075

Figure 74. SPI Read Transaction with CRC

If checksum protection is enabled when continuous read mode

is active, an implied read data command of 0x44 before every

data transmission must be accounted for when calculating the

checksum value. This implied read data command ensures a

nonzero checksum value even if the ADC data equals 0x000000.

AD7172-2 Data Sheet

Rev. A | Page 42 of 60

CRC CALCULATION

Polynomial

The checksum, which is eight bits wide, is generated using the

polynomial

x8 + x2 + x + 1

To generate the checksum, the data is left shifted by eight bits to

create a number ending in eight Logic 0s.

The polynomial is aligned so that the MSB is adjacent to the

leftmost Logic 1 of the data. An XOR function is applied to the

data to produce a new, shorter number. The polynomial is again

aligned so that the MSB is adjacent to the leftmost Logic 1 of the

new result, and the procedure is repeated. This process repeats

until the original data is reduced to a value less than the

polynomial. This is the 8-bit checksum.

Example of a Polynomial CRC Calculation—24-Bit Word: 0x654321 (8-Bit Command and 16-Bit Data)

An example of generating the 8-bit checksum using the polynomial based checksum is as follows:

Initial value 011001010100001100100001

01100101010000110010000100000000 left shifted eight bits

x8 + x2 + x + 1 = 100000111 polynomial

100100100000110010000100000000 XOR result

100000111 polynomial

100011000110010000100000000 XOR result

100000111 polynomial

11111110010000100000000 XOR result

100000111 polynomial value

1111101110000100000000 XOR result

100000111 polynomial value

111100000000100000000 XOR result

100000111 polynomial value

11100111000100000000 XOR result

100000111 polynomial value

1100100100100000000 XOR result

100000111 polynomial value

100101010100000000 XOR result

100000111 polynomial value

101101100000000 XOR result

100000111 polynomial value

1101011000000 XOR result

100000111 polynomial value

101010110000 XOR result

100000111 polynomial value

1010001000 XOR result

100000111 polynomial value

10000110 checksum = 0x86

Data Sheet AD7172-2

Rev. A | Page 43 of 60

XOR Calculation

The checksum, which is 8 bits wide, is generated by splitting the data into bytes and then performing an XOR of the bytes.

Example of an XOR Calculation—24-Bit Word: 0x654321 (8-Bit Command and 16-Bit Data)

Using the previous example, divide into three bytes: 0x65, 0x43, and 0x21

01100101 0x65

01000011 0x43

00100110 XOR result

00100001 0x21

00000111 CRC

AD7172-2 Data Sheet

Rev. A | Page 44 of 60

INTEGRATED FUNCTIONS

The AD7172-2 has integrated functions that improve the

usefulness of a number of applications as well as serve

diagnostic purposes in safety conscious applications.

GENERAL-PURPOSE INPUT/OUTPUT

The AD7172-2 has two general-purpose digital input/output

pins: GPIO0 and GPIO1. They are enabled using the IP_EN0/

IP_EN1 bits or the OP_EN0/OP_EN1 bits in the GPIOCON

logic level at the pin is contained in the GP_DATA0 or GP_DATA1

bit, respectively. When the GPIO0 or GPIO1 pin is enabled as an

output, the GP_ DATA0 or GP_DATA1 bits, respectively,

determine the logic level output at the pin. The logic levels for

these pins are referenced to AVDD1 and AVSS; therefore, outputs

have an amplitude of 5 V or 3.3 V.

The SYNC/ERROR pin can also be used as a general-purpose

output. When the ERR_EN bits in the GPIOCON register are

set to 11, the SYNC/ERRORA pin operates as a general-purpose

output. In this configuration, the ERR_DAT bit in the GPIOCON

for the pin is referenced to IOVDD and DGND.

The GPIO0 pin, GPIO1 pin, and SYNC/ERROR pin, when set as

general-purpose outputs, have an active pull-up.

EXTERNAL MULTIPLEXER CONTROL

If an external multiplexer increases the channel count, the

multiplexer logic pins can be controlled via the AD7172-2

GPIOx pins. With the MUX_IO bit (Bit 12 in the GPIOCON

the channel change is synchronized with the ADC, eliminating

any need for external synchronization.

DELAY

It is possible to insert a programmable delay before the AD7172-2

begins to take samples. This delay allows an external amplifier

or multiplexer to settle and can also alleviate the specification

requirements for the external amplifier or multiplexer. Eight

programmable settings, ranging from 0 µs to 8 ms, can be set

using the delay bits in the ADC mode register (Register 0x01,

Bits[10:8]).

If a delay greater than 0 µs is selected and the HIDE_DELAY bit

in the ADC mode register is set to 0, this delay is added to the

conversion time, regardless of selected output data rate.

When using the sinc5 + sinc1 filter, it is possible to hide this

delay so the output data rate remains the same as the output data

rate without the delay enabled. If the HIDE_DELAY bit is set to

1 and the selected delay is less than half of the conversion time,

the delay can be absorbed by reducing the number of averages

the digital filter performs, which keeps the conversion time the

same but can affect the noise performance.

The effect on the noise performance depends on the delay time

compared to the conversion time. It is possible to absorb the

delay only for output data rates less than 2.6 kSPS with the

exception of the following four rates, which cannot absorb any

delay: 381 SPS, 59.52 SPS, 49.68 SPS, and 16.66 SPS.

16-BIT/24-BIT CONVERSIONS

By default, the AD7172-2 generates 24-bit conversions. However,

the width of the conversions can be reduced to 16 bits. Setting the

WL16 bit in the interface mode register to 1 rounds all data

conversions to 16 bits. Clearing this bit sets the width of the

data conversions to 24 bits.

DOUT_RESET

The serial interface uses a shared DOUT/RDY pin. By default,

this pin outputs the RDY signal. During a data read, this pin

outputs the data from the register being read. After the read is

complete, the pin reverts to outputting the RDY signal after a

short fixed period of time (t7). However, this time may be too

short for some microcontrollers and can be extended until the

CS pin is brought high by setting the DOUT_RESET bit in the

interface mode register to 1. This setting means CS must frame

each read operation and compete the serial interface transaction.

SYNCHRONIZATION

Normal Synchronization

When the SYNC_EN bit in the GPIOCON register is set to 1,

the SYNC/ERROR pin functions as a synchronization input.

The SYNC input allows the user to reset the modulator and the

digital filter without affecting any of the setup conditions on the

device. This feature allows the user to start to gather samples of

the analog input from a known point, the rising edge of the SYNC

input. The SYNC input must be low for at least one master clock

cycle to ensure that synchronization occurs.

If multiple AD7172-2 devices are operated from a common

master clock, they can be synchronized so the analog inputs

aresampled simultaneously. This synchronization is typically

completed after each AD7172-2 device has performed each

respective calibration or has calibration coefficients loaded into the

calibration registers. A falling edge on the SYNC input resets the

digital filter and the analog modulator and places the AD7172-2

into a consistent known state. While the SYNC input is low, the

AD7172-2 is maintained in this known state. On the SYNC input

rising edge, the modulator and filter are taken out of this reset state,

and on the next master clock edge, the device starts to gather

input samples again.

Data Sheet AD7172-2

Rev. A | Page 45 of 60

The device is taken out of reset on the master clock falling edge

following the SYNC input low to high transition. Therefore,

when multiple devices are being synchronized, take the SYNC

Ainput high on the master clock rising edge to ensure that all

devices are released on the master clock falling edge. If the

SYNC input is not taken high in sufficient time, a difference of

one master clock cycle between the devices is possible, that is,

the instant at which conversions are available differs from

device to device by a maximum of one master clock cycle.

The SYNC input can also be used as a start conversion

command for a single channel when in normal synchronization

mode. In this mode, the rising edge of SYNC input starts a

conversion, and the falling edge of the RDY output indicates when

the conversion is complete. The settling time of the filter is

required for each data register update. After the conversion is

complete, bring the SYNC input low in preparation for the next

conversion start signal.

Alternate Synchronization

In alternate synchronization mode, the SYNC input operates as

a start conversion command when several channels of the

AD7172-2 are enabled. Setting the ALT_SYNC bit in the interface

mode register to 1 enables an alternate synchronization scheme.

When the SYNC input is taken low, the ADC completes the

conversion on the current channel, selects the next channel in

the sequence, and then waits until the SYNC input is taken high

to start the conversion. The RDY output goes low when the

conversion is complete on the current channel, and the data

Therefore, the SYNC input does not interfere with the sampling

on the currently selected channel but allows the user to control

the instant at which the conversion begins on the next channel

in the sequence.

Alternate synchronization mode can be used only when several

channels are enabled. It is not recommended to use this mode

when a single channel is enabled.

ERROR FLAGS

The status register contains three error bits (ADC_ERROR,

CRC_ERROR, and REG_ERROR) that flag errors with the

ADC conversion, errors with the CRC check, and errors caused

by changes in the registers, respectively. In addition, the ERROR

output can indicate that an error has occurred.

ADC_ERROR

The ADC_ERROR bit in the status register flags any errors that

occur during the conversion process. The flag is set when an over-

range or underrange result is output from the ADC. The ADC

also outputs all 0s or all 1s when an undervoltage or overvoltage

occurs. This flag is reset only when the overvoltage or undervoltage

condition is removed. This flag is not reset by a read of the data

CRC_ERROR

If the CRC value that accompanies a write operation does not

correspond with the information sent, the CRC_ERROR flag is

set. The flag is reset when the status register is explicitly read.

REG_ERROR

The REG_ERROR flag is used in conjunction with the

REG_CHECK bit in the interface mode register. When the

REG_CHECK bit is set, the AD7172-2 monitors the values in

the on-chip registers. If a bit changes, the REG_ERROR bit is set

to 1. Therefore, for writes to the on-chip registers, set the

REG_CHECK bit to 0. When the registers have been updated, the

REG_CHECK bit can be set to 1. The AD7172-2 calculates a

checksum of the on-chip registers. If one of the register values

has changed, the REG_ERROR bit is set to 1. If an error is flagged,

the REG_CHECK bit must be set to 0 to clear the REG_ERROR

bit in the status register. The register check function does not

monitor the data register, status register, or interface mode register.

ERROR Input/Output

When the SYNC_EN bit in the GPIOCON register is set to 0,

the SYNC/ERROR pin functions as an error input/output pin or

a general-purpose output pin. The ERR_EN bits in the GPIOCON

When the ERR_EN bits are set to 10, the SYNC/ERROR pin

functions as an open-drain error output, ERROR. The three

error bits in the status register (ADC_ERROR, CRC_ERROR, and

REG_ERROR) are OR’ed, inverted, and mapped to the ERROR

output. Therefore, the ERROR output indicates that an error has

occurred. The status register must be read to identify the error

source.

When the ERR_EN bits are set to 01, the SYNC/ERROR pin

functions as an error input, ERROR. The error output of another

component can be connected to the AD7172-2 ERROR input so

that the AD7172-2 indicates when an error occurs on either itself

or the external component. The value on the ERROR input is

inverted and OR’ed with the errors from the ADC conversion,

and the result is indicated via the ADC_ERROR bit in the status

ERR_DAT bit in the GPIO configuration register.

The ERROR input/output is disabled when the ERR_EN bits are set

to 00. When the ERR_EN bits are set to 11, the SYNC/ERROR pin

operates as a general-purpose output.

DATA_STAT

The contents of the status register can be appended to each con-

version on the AD7172-2 using the DATA_STAT bit in the

IFMODE register. This function is useful if several channels are

enabled. Each time a conversion is output, the contents of the

status register are appended. The two LSBs of the status register

indicate to which channel the conversion corresponds. In

addition, the user can determine if any errors are being flagged

by the error bits.

AD7172-2 Data Sheet

Rev. A | Page 46 of 60

IOSTRENGTH

The serial interface can operate with a power supply as low as

2 V. However, at this low voltage, the DOUT/RDY pin may not

have sufficient drive strength if there is moderate parasitic

capacitance on the board or if the SCLK frequency is high. The

IOSTRENGTH bit in the interface mode register increases the

drive strength of the DOUT/RDY pin.

INTERNAL TEMPERATURE SENSOR

The AD7172-2 has an integrated temperature sensor. The

temperature sensor can be used as a guide for the ambient

temperature at which the device is operating. This can be used

for diagnostic purposes or as an indicator of when the application

circuit must rerun a calibration routine to take into account a shift

in operating temperature. The temperature sensor is selected using

the crosspoint multiplexer and is selected in the same way as an

analog input channel.

The temperature sensor requires that the analog input buffers

be enabled on both analog inputs. If the buffers are not enabled,

selecting the temperature sensor as an input forces the buffers

to be enabled during the conversion.

To use the temperature sensor, the first step is to calibrate the

device in a known temperature (25°C) and take a conversion as

a reference point. The temperature sensor has a nominal sensitivity

of 477 µV/K; the difference in this ideal slope and the slope

measured can calibrate the temperature sensor. The temperature

sensor is specified with a ±2°C typical accuracy after calibration

at 25°C. The temperature can be calculated as follows:

15.273–

μV477

)( 













=° ResultConversion

CeTemperatur

Data Sheet AD7172-2

Rev. A | Page 47 of 60

GROUNDING AND LAYOUT

The analog inputs and reference inputs are differential and,

therefore, most of the voltages in the analog modulator are

common-mode voltages. The high common-mode rejection of

the device removes common-mode noise on these inputs. The

analog and digital supplies to the AD7172-2 are independent

and connected to separate pins to minimize coupling between the

analog and digital sections of the device. The digital filter provides

rejection of broadband noise on the power supplies, except at

integer multiples of the master clock frequency.

The digital filter also removes noise from the analog and reference

inputs, provided that these noise sources do not saturate the analog

modulator. As a result, the AD7172-2 is more immune to noise

interference than a conventional high resolution converter.

However, because the resolution of the AD7172-2 is high and

the noise levels from the converter are so low, take care with

regard to grounding and layout.

The PCB that houses the ADC must be designed such that the

analog and digital sections are separated and confined to

certain areas of the board. A minimum etch technique is

generally best for ground planes because it results in the best

shielding.

In any layout, the user must consider the flow of currents in the

system, ensuring that the paths for all return currents are as close as

possible to the paths the currents took to reach their destinations.

Avoid running digital lines under the device because this

couples noise onto the die. Allow the analog ground plane to

run under the AD7172-2 to prevent noise coupling. The power

supply lines to the AD7172-2 must use as wide a trace as

possible to provide low impedance paths and reduce glitches on

the power supply line. Shield fast switching signals like clocks

with digital ground to prevent radiating noise to other sections

of the board, and never run clock signals near the analog inputs.

Avoid crossover of digital and analog signals. Run traces on

opposite sides of the board at right angles to each other. This

technique reduces the effects of feedthrough on the board. A

microstrip technique is by far the best but is not always possible

with a double-sided board.

Good decoupling is important when using high resolution ADCs.

The AD7172-2 has three power supply pins: AV DD1, AVDD2,

and IOVDD. The AVDD1 and AVDD2 pins are referenced to

AVSS, and the IOVDD pin is referenced to DGND. Decouple

AVDD1 and AVDD2 with a 10 µF capacitor in parallel with a

0.1 µF capacitor to AVSS on each pin. Place the 0.1 µF capacitor

as close as possible to the device on each supply, ideally right up

against the device. Decouple IOVDD with a 10 µF capacitor in

parallel with a 0.1 µF capacitor to DGND. Decouple all analog

inputs to AVSS. If an external reference is used, decouple the

REF+ and REF− pins to AVSS.

The AD7172-2 also has two on-board LDO regulators, one that

regulates the AVDD2 supply and one that regulates the IOVDD

supply. For the REGCAPA pin, use 1 µF and 0.1 µF capacitors to

AVSS. Similarly, for the REGCAPD pin, use 1 µF and 0.1 µF

capacitors to DGND.

If using the AD7172-2 for split supply operation, a separate

plane must be used for AVSS.

AD7172-2 Data Sheet

Rev. A | Page 48 of 60

Table 25. Register Summary

Reg.

Name

Bits

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

Reset

0x00 COMMS [7:0] WEN R/W RA 0x00 W

0x00 STATUS [7:0] RDY ADC_ERROR CRC_ERROR REG_ERROR RESERVED CHANNEL 0x80 R

0x01 ADCMODE [15:8] REF_EN HIDE_DELAY SING_CYC RESERVED DELAY 0x0000 RW

[7:0] RESERVED MODE CLOCKSEL RESERVED

0x02 IFMODE [15:8] RESERVED ALT_SYNC IOSTRENGTH RESERVED DOUT_RESET 0x0000 RW

[7:0] CONTREAD DATA_STAT REG_CHECK RESERVED CRC_EN RESERVED WL16

0x03

REGCHECK

[23:16]

REGISTER_CHECK[23:16]

0x000000

[15:8] REGISTER_CHECK[15:8]

[7:0] REGISTER_CHECK[7:0]

0x04 DATA [23:16] DATA[23:16] 0x000000 R

[15:8] DATA[15:8]

[7:0] DATA[7:0]

0x06 GPIOCON [15:8] RESERVED MUX_IO SYNC_EN ERR_EN ERR_DAT 0x0800 RW

[7:0] RESERVED IP_EN1 IP_EN0 OP_EN1 OP_EN0 GP_DATA1 GP_DATA0

0x07 ID [15:8] ID[15:8] 0x00DX R

[7:0] ID[7:0]

0x10 CH0 [15:8] CH_EN0 RESERVED SETUP_SEL0 RESERVED AINPOS0[4:3] 0x8001 RW

[7:0] AINPOS0[2:0] AINNEG0

0x11 CH1 [15:8] CH_EN1 RESERVED SETUP_SEL1 RESERVED AINPOS1[4:3] 0x0001 RW

[7:0] AINPOS1[2:0] AINNEG1

0x12 CH2 [15:8] CH_EN2 RESERVED SETUP_SEL2 RESERVED AINPOS2[4:3] 0x0001 RW

[7:0] AINPOS2[2:0] AINNEG2

0x13 CH3 [15:8] CH_EN3 RESERVED SETUP_SEL3 RESERVED AINPOS3[4:3] 0x0001 RW

[7:0] AINPOS3[2:0] AINNEG3

0x20 SETUPCON0 [15:8] RESERVED BI_UNIPOLAR0 REFBUF0+ REFBUF0− AINBUF0+ AINBUF0− 0x1000 RW

[7:0] BURNOUT_EN0

RESERVED REF_SEL0 RESERVED

0x21 SETUPCON1 [15:8] RESERVED BI_UNIPOLAR1 REFBUF1+ REFBUF1− AINBUF1+ AINBUF1− 0x1000 RW

[7:0] BURNOUT_EN1

RESERVED REF_SEL1 RESERVED

0x22 SETUPCON2 [15:8] RESERVED BI_UNIPOLAR2 REFBUF2+ REFBUF2− AINBUF2+ AINBUF2− 0x1000 RW

[7:0] BURNOUT_EN2

RESERVED REF_SEL2 RESERVED

0x23 SETUPCON3 [15:8] RESERVED BI_UNIPOLAR3 REFBUF3+ REFBUF3− AINBUF3+ AINBUF3− 0x1000 RW

[7:0] BURNOUT_EN3

RESERVED REF_SEL3 RESERVED

0x28 FILTCON0 [15:8] SINC3_MAP0 RESERVED ENHFILTEN0 ENHFILT0 0x0500 RW

[7:0] RESERVED ORDER0 ODR0

0x29 FILTCON1 [15:8] SINC3_MAP1 RESERVED ENHFILTEN1 ENHFILT1 0x0500 RW

[7:0] RESERVED ORDER1 ODR1

0x2A FILTCON2 [15:8] SINC3_MAP2 RESERVED ENHFILTEN2 ENHFILT2 0x0500 RW

[7:0] RESERVED ORDER2 ODR2

0x2B FILTCON3 [15:8] SINC3_MAP3 RESERVED ENHFILTEN3 ENHFILT3 0x0500 RW

[7:0] RESERVED ORDER3 ODR3

0x30 OFFSET0 [23:0] OFFSET0[23:0] 0x800000 RW

0x31 OFFSET1 [23:0] OFFSET1[23:0] 0x800000 RW

0x32 OFFSET2 [23:0] OFFSET2[23:0] 0x800000 RW

0x33 OFFSET3 [23:0] OFFSET3[23:0] 0x800000 RW

0x38 GAIN0 [23:0] GAIN0[23:0] 0x5XXXX0 RW

0x39 GAIN1 [23:0] GAIN1[23:0] 0x5XXXX0 RW

0x3A GAIN2 [23:0] GAIN2[23:0] 0x5XXXX0 RW

0x3B GAIN3 [23:0] GAIN3[23:0] 0x5XXXX0 RW

Data Sheet AD7172-2

Rev. A | Page 49 of 60

COMMUNICATIONS REGISTER

Address: 0x00, Reset: 0x00, Name: COMMS

All access to the on-chip registers must start with a write to the communications register. This write determines what register is accessed

next and whether that operation is a write or a read.

Table 26. Bit Descriptions for COMMS

Bits

Bit Name

Settings

Description

Reset

Access

7 WEN This bit must be low to begin communications with the ADC. 0x0 W

6 R/W This bit determines if the command is a read or write operation. 0x0 W

0 Write command

1 Read command

[5:0] RA The register address bits determine which register is to be read from or

written to as part of the current communication.

0x00 W

000000 Status register

000001 ADC mode register

000010 Interface mode register

000011 Register check register

000100 Data register

000110 GPIO configuration register

000111 ID register

010000 Channel Register 0

010001 Channel Register 1

010010 Channel Register 2

010011 Channel Register 3

100000 Setup Configuration Register 0

100001

Setup Configuration Register 1

100010 Setup Configuration Register 2

100011 Setup Configuration Register 3

101000 Filter Configuration Register 0

101001 Filter Configuration Register 1

101010 Filter Configuration Register 2

101011 Filter Configuration Register 3

110000 Offset Register 0

110001 Offset Register 1

110010 Offset Register 2

110011 Offset Register 3

111000 Gain Register 0

111001 Gain Register 1

111010 Gain Register 2

111011 Gain Register 3

AD7172-2 Data Sheet

Rev. A | Page 50 of 60

STATUS REGISTER

Address: 0x00, Reset: 0x80, Name: STATUS

The status register is an 8-bit register that contains ADC and serial interface status information. It can optionally be appended to the data

Table 27. Bit Descriptions for STATUS

Bits Bit Name Settings Description Reset Access

7 RDY The status of RDY is output to the DOUT/RDY pin whenever CS is low and

a register is not being read. This bit goes low when the ADC has written a

new result to the data register. In ADC calibration modes, this bit goes low

when the ADC has written the calibration result. RDY is brought high

automatically by a read of the data register.

0x1 R

0 New data result available

1 Awaiting new data result

6 ADC_ERROR This bit by default indicates if an ADC overrange or underrange has

occurred. The ADC result is clamped to 0xFFFFFF for overrange errors and

0x000000 for underrange errors. This bit is updated when the ADC result is

written and is cleared at the next update after removing the overrange or

underrange condition.

0x0 R

No error

1 Error

5 CRC_ERROR This bit indicates if a CRC error has taken place during a register write. For

occurred. This bit is cleared by a read of this register.

0x0 R

0 No error

1 CRC error

4 REG_ERROR This bit indicates if the content of one of the internal registers has

changed from the value calculated when the register integrity check was

activated. The check is activated by setting the REG_CHECK bit in the

interface mode register. This bit is cleared by clearing the REG_CHECK bit.

0x0 R

0 No error

1 Error

[3:2] RESERVED These bits are reserved. 0x0 R

[1:0] CHANNEL These bits indicate which channel was active for the ADC conversion

whose result is currently in the data register. This channel may be different

from the channel currently being converted. The mapping is a direct map

from the channel register; therefore, Channel 0 results in 0x0 and Channel

3 results in 0x3.

0x0 R

00 Channel 0

01 Channel 1

10 Channel 2

Channel 3

Data Sheet AD7172-2

Rev. A | Page 51 of 60

ADC MODE REGISTER

Address: 0x01, Reset: 0x0000, Name: ADCMODE

The ADC mode register controls the operating mode of the ADC and the master clock selection. A write to the ADC mode register resets

the filter and the ARDYA bits and starts a new conversion or calibration.

Table 28. Bit Descriptions for ADCMODE

Bits Bit Name Settings Description Reset Access

15 REF_EN This bit enables the internal reference and outputs a buffered 2.5 V to the

REFOUT pin.

0x0 RW

0 Disabled

1 Enabled

HIDE_DELAY

If a programmable delay is set using the DELAY bits, this bit allows the

delay to be hidden by absorbing the delay into the conversion time for

selected data rates with the sinc5 + sinc1 filter. See the Delay section for

more information.

0x0

0 Enabled

Disabled

13 SING_CYC This bit can be used when only a single channel is active to set the ADC to

only output at the settled filter data rate.

0x0 RW

0 Disabled

Enabled

[12:11] RESERVED These bits are reserved; set these bits to 0. 0x0 R

[10:8] DELAY

These bits allow a programmable delay to be added after a channel switch

to allow settling of external circuitry before the ADC starts processing the

input.

0x0 RW

000 0 µs

001 32 µs

010 128 µs

011 320 µs

100 800 µs

101 1.6 ms

110 4 ms

111 8 ms

7 RESERVED This bit is reserved; set this bit to 0. 0x0 R

[6:4] MODE These bits control the operating mode of the ADC. See the Operating

Modes section for more information.

0x0 RW

000 Continuous conversion mode

001 Single conversion mode

010 Standby mode

011 Power-down mode

100 Internal offset calibration

110 System offset calibration

111

System gain calibration

[3:2] CLOCKSEL This bit selects the ADC clock source. Selecting internal oscillator also

enables the internal oscillator.

0x0 RW

00 Internal oscillator

01 Internal oscillator output on the XTAL2/CLKIO pin

10 External clock input on the XTAL2/CLKIO pin

11 External crystal on the XTAL1 and XTAL2/CLKIO pins

[1:0] RESERVED These bits are reserved; set these bits to 0. 0x0 R

AD7172-2 Data Sheet

Rev. A | Page 52 of 60

INTERFACE MODE REGISTER

Address: 0x02, Reset: 0x0000, Name: IFMODE

The interface mode register configures various serial interface options.

Table 29. Bit Descriptions for IFMODE

Bits Bit Name Settings Description Reset Access

[15:13] RESERVED These bits are reserved; set these bits to 0. 0x0 R

12 ALT_SYNC This bit enables a different behavior of the SYNC/ERROR pin to allow the

use of SYNC/ERROR as a control for conversions when cycling channels

(see the description of the SYNC_EN bit in the GPIO Configuration Register

section for details).

0x0 RW

0 Disabled

1 Enabled

11 IOSTRENGTH This bit controls the drive strength of the DOUT/RDY pin. Set this bit when

reading from the serial interface at high speed with a low IOVDD supply

and moderate capacitance.

0x0 RW

0 Disabled (default)

1 Enabled

[10:9] RESERVED These bits are reserved; set these bits to 0. 0x0 R

8 DOUT_RESET See the DOUT_RESET section for more information. 0x0 RW

0 Disabled

1 Enabled

7 CONTREAD This bit enables a continuous read of the ADC data register. The ADC must

be configured in continuous conversion mode to use continuous read. For

more details, see the Operating Modes section.

0x0 RW

0 Disabled

1 Enabled

6 DATA_STAT This enables the status register to be appended to the data register when

read so that the channel and status information are transmitted with the

data. This is the only way to ensure that the channel bits read from the

status register correspond to the data in the data register.

0x0 RW

0 Disabled

1 Enabled

5 REG_CHECK This bit enables a register integrity checker, which can monitor any change in

the value of the user registers. To use this feature, configure all other registers

as desired, with this bit cleared. Then write to this register to set the

REG_CHECK bit to 1. If the contents of any of the registers change, the

REG_ERROR bit is set in the status register. To clear the error, set the

REG_CHECK bit to 0. Neither the interface mode register nor the ADC data

or status registers are included in the registers that are checked. If a register

must have a new value written, this bit must first be cleared; otherwise,

an error is flagged when the new register contents are written.

0x0 RW

0 Disabled

1 Enabled

4 RESERVED This bit is reserved; set this bit to 0. 0x0 R

[3:2] CRC_EN These bits enable CRC protection of register reads/writes. CRC increases

the number of bytes in a serial interface transfer by one. See the CRC

Calculation section for more details.

0x00 RW

00 Disabled

01 XOR checksum enabled for register read transactions; register writes still

use CRC with these bits set

10 CRC checksum enabled for read and write transactions

1 RESERVED This bit is reserved; set this bit to 0. 0x0 R

Data Sheet AD7172-2

Rev. A | Page 53 of 60

Bits Bit Name Settings Description Reset Access

0 WL16 This bit changes the ADC data register to 16 bits. The ADC is not reset by a

write to the interface mode register; therefore, the ADC result is not

rounded to the correct word length immediately after writing to this bit.

The first new ADC result is correct.

0x0 RW

24-bit data

1 16-bit data

Address: 0x03, Reset: 0x000000, Name: REGCHECK

The register check register is a 24-bit checksum calculated by exclusively OR'ing the contents of the user registers. The REG_CHECK bit

in the interface mode register must be set for this register to operate; otherwise, the register reads 0.

Table 30. Bit Descriptions for REGCHECK

Bits Bit Name Settings Description Reset Access

[23:0] REGISTER_CHECK This register contains the 24-bit checksum of user registers when the

REG_CHECK bit is set in the interface mode register.

0x000000 R

DATA REGISTER

Address: 0x04, Reset: 0x000000, Name: DATA

The data register contains the ADC conversion result. The encoding is offset binary, or it can be changed to unipolar by the

BI_UNIPOLARx bit in the setup configuration registers. Reading the data register brings the RDY bit and the RDY output high if they are

low. The ADC result can be read multiple times; however, because the RDY output has been brought high, it is not possible to know if

another ADC result is imminent. After the command to read the ADC register is received, the ADC does not write a new result into the

data register.

Table 31. Bit Descriptions for DATA

Bits Bit Name Settings Description Reset Access

[23:0] DATA This register contains the ADC conversion result. If the DATA_STAT bit is

set in the interface mode register, the status register is appended to this

the interface mode register, this register is reduced to 16 bits.

0x000000 R

AD7172-2 Data Sheet

Rev. A | Page 54 of 60

GPIO CONFIGURATION REGISTER

Address: 0x06, Reset: 0x0800, Name: GPIOCON

The GPIO configuration register controls the general-purpose input/output pins of the ADC.

Table 32. Bit Descriptions for GPIOCON

Bits Bit Name Settings Description Reset Access

[15:13] RESERVED These bits are reserved; set these bits to 0. 0x0 R

12 MUX_IO This bit allows the ADC to control an external multiplexer, using GPIO0/GPIO1 in sync

with the internal channel sequencing. The analog input pins used for a channel

can still be selected on a per channel basis. Therefore, it is possible to have a

4-channel multiplexer in front of AIN0/AIN1 and another in front of AIN2/AIN3, giving a

total of eight differential channels with the AD7172-2. However, only four channels at a

time can be automatically sequenced. A delay can be inserted after switching an

external multiplexer (see the delay bits in the ADC Mode Register section).

0x0 RW

11 SYNC_EN This bit enables the SYNC/ERROR pin as a sync input. When the pin is low, this bit

holds the ADC and filter in reset until the SYNC/ERROR pin goes high. An alternative

operation of the SYNC/ERROR pin is available when the ALT_SYNC bit in the interface

mode register is set. This mode only works when multiple channels are enabled. In

this case, a low on the SYNC/ERROR pin does not immediately reset the filter/

modulator. Instead, if the SYNC/ERROR pin is low when the channel is due to be

switched, the modulator and filter are prevented from starting a new conversion.

Bringing SYNC/ERROR high begins the next conversion. This alternative sync mode

allows SYNC/ERROR to be used while cycling through channels.

0x1 RW

0 Disabled.

1 Enabled.

[10:9] ERR_EN These bits enable the SYNC/ERROR pin as an error input/output. 0x0 RW

00 Disabled.

01 SYNC/ERROR is an error input. The (inverted) readback state is OR'ed with other

error sources and is available in the ADC_ERROR bit in the status register. The SYNC/

ERROR pin state can also be read from the ERR_DAT bit in this register.

10 SYNC/ERROR is an open-drain error output. The status register error bits are OR'ed,

inverted, and mapped to the SYNC/ERROR pin. The SYNC/ERROR pins of multiple

devices can be wired together to a common pull-up resistor so that an error on

any device can be observed.

11 SYNC/ERROR is a general-purpose output. The status of the pin is controlled by the

ERR_DAT bit in this register. This output is referenced between IOVDD and DGND,

as opposed to the AVDD1 and AVSS levels used by the general-purpose input/output

pins. The SYNC/ERROR pin has an active pull-up in this case.

8 ERR_DAT This bit determines the logic level at the SYNC/ERROR pin if the pin is enabled as a

general-purpose output. This bit reflects the readback status of the pin if the pin is

enabled as an input.

0x0 RW

[7:6]

RESERVED

These bits are reserved; set these bits to 0.

0x0

5 IP_EN1 This bit turns GPIO1 into an input. Inputs are referenced to AVDD1 or AVSS. 0x0 RW

0 Disabled.

1 Enabled.

4 IP_EN0 This bit turns GPIO0 into an input. Inputs are referenced to AVDD1 or AVSS. 0x0 RW

0 Disabled.

1 Enabled.

3 OP_EN1 This bit turns GPIO1 into an output. Outputs are referenced between AVDD1 and AVSS. 0x0 RW

0 Disabled.

1 Enabled.

OP_EN0

This bit turns GPIO0 into an output. Outputs are referenced between AVDD1 and AVSS.

0x0

Disabled.

1 Enabled.

1 GP_DATA1 This bit is the readback or write data for GPIO1. 0x0 RW

0 GP_DATA0 This bit is the readback or write data for GPIO0. 0x0 RW

Data Sheet AD7172-2

Rev. A | Page 55 of 60

ID REGISTER

Address: 0x07, Reset: 0x00DX, Name: ID

The ID register returns a 16-bit ID. For the AD7172-2, this ID is 0x00DX.

Table 33. Bit Descriptions for ID

Bits Bit Name Settings Description Reset Access

[15:0] ID The ID register returns a 16-bit ID code that is specific to the ADC. 0x00DX R

0x00DX AD7172-2

CHANNEL REGISTER 0

Address: 0x10, Reset: 0x8001, Name: CH0

The channel registers are 16-bit registers that select which channels are currently active, which inputs are selected for each channel, and

which setup configures the ADC for that channel.

Table 34. Bit Descriptions for CH0

Bits Bit Name Settings Description Reset Access

15 CH_EN0 This bit enables Channel 0. If more than one channel is enabled, the ADC

automatically sequences between them.

0x1 RW

0 Disabled

1 Enabled (default)

14 RESERVED This bit is reserved; set this bit to 0. 0x0 R

[13:12] SETUP_SEL0 These bits identify which of the four setups configure the ADC for this

channel. A setup comprises a set of four registers: setup configuration register,

filter configuration register, offset register, and gain register. All channels

can use the same setup, in which case the same 2-bit value must be written

to these bits on all active channels, or up to four channels can be

configured differently.

0x0 RW

00 Setup 0

01 Setup 1

Setup 2

11 Setup 3

[11:10] RESERVED These bits are reserved; set these bits to 0. 0x0 R

[9:5] AINPOS0 These bits select which input is connected to the positive input of the

ADC for this channel.

0x0 RW

00000 AIN0 (default)

00001 AIN1

00010 AIN2

00011 AIN3

00100 AIN4

10001 Temperature sensor+

10010

Temperature sensor−

10011 ((AVDD1 − AVSS)/5)+ (analog input buffers must be enabled)

10100 ((AVDD1 − AVSS)/5)− (analog input buffers must be enabled)

10101 REF+

10110 REF−

AD7172-2 Data Sheet

Rev. A | Page 56 of 60

Bits Bit Name Settings Description Reset Access

[4:0] AINNEG0 These bits select which input is connected to the negative input of the

ADC for this channel.

0x1 RW

00000 AIN0

00001 AIN1 (default)

00010 AIN2

00011 AIN3

00100 AIN4

10001 Temperature sensor+

10010 Temperature sensor−

10011 ((AVDD1 − AVSS)/5)+

10100

((AVDD1 − AVSS)/5)−

10101 REF+

10110 REF−

CHANNEL REGISTER 1 TO CHANNEL REGISTER 3

Address: 0x11, 0x12, 0x13, Reset: 0x0001, Name: CH1 to CH3

The remaining three channel registers share the same layout as Channel Register 0.

Table 35. CH1 to CH3 Register Map

Reg.

Name

Bits

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

Reset

0x11

CH1

[15:8]

CH_EN1

RESERVED

SETUP_SEL1

RESERVED

AINPOS1[4:3]

0x0001

[7:0]

AINPOS1[2:0]

AINNEG1

0x12

CH2

[15:8]

CH_EN2

RESERVED

SETUP_SEL2

RESERVED

AINPOS2[4:3]

0x0001

[7:0]

AINPOS2[2:0]

AINNEG2

0x13

CH3

[15:8]

CH_EN3

RESERVED

SETUP_SEL3

RESERVED

AINPOS3[4:3]

0x0001

[7:0]

AINPOS3[2:0]

AINNEG3

Data Sheet AD7172-2

Rev. A | Page 57 of 60

SETUP CONFIGURATION REGISTER 0

Address: 0x20, Reset: 0x1000, Name: SETUPCON0

The setup configuration registers are 16-bit registers that configure the reference selection, input buffers, and output coding of the ADC.

Table 36. Bit Descriptions for SETUPCON0

Bits Bit Name Settings Description Reset Access

[15:13] RESERVED These bits are reserved; set these bits to 0. 0x0 R

12 BI_UNIPOLAR0 This bit sets the output coding of the ADC for Setup 0. 0x1 RW

0 Unipolar coded output

1 Bipolar coded output (offset binary)

11 REFBUF0+ This bit enables or disables the REF+ input buffer. 0x0 RW

0 REF+ buffer disabled

1 REF+ buffer enabled

10 REFBUF0− This bit enables or disables the REF− input buffer. 0x0 RW

0 REF− buffer disabled

1 REF− buffer enabled

AINBUF0+

This bit enables or disables the AIN+ input buffer.

0x0

0 AIN+ buffer disabled

1 AIN+ buffer enabled

8 AINBUF0− This bit enables or disables the AIN− input buffer. 0x0 RW

0 AIN− buffer disabled

1 AIN− buffer enabled

7 BURNOUT_EN0 This bit enables a 10 µA current source on the positive analog input

selected and a 10 µA current sink on the negative analog input selected.

The burnout currents are useful in diagnosis of an open wire, whereby the

ADC result goes to full scale. Enabling the burnout currents during

measurement results in an offset voltage on the ADC. The best strategy for

diagnosing an open wire is turning on the burnout currents at intervals,

before or after precision measurements.

0x00 R

6 RESERVED These bits are reserved; set these bits to 0. 0x00 R

[5:4] REF_SEL0 These bits allow you to select the reference source for ADC conversion on

Setup 0.

0x0 RW

00 External reference.

10 Internal 2.5 V reference. The REF_EN bit must also be enabled in the ADC

mode register.

11 AVDD1 − AVSS. This can be used to as a diagnostic to validate other

reference values.

[3:0] RESERVED These bits are reserved; set these bits to 0. 0x0 R

SETUP CONFIGURATION REGISTER 1 TO SETUP CONFIGURATION REGISTER 3

Address: 0x21, 0x22, 0x23, Reset: 0x1000, Name: SETUPCON1 to SETUPCON3

The remaining three setup configuration registers share the same layout as Setup Configuration Register 0.

Table 37. SETUPCON1 to SETUPCON3 Register Map

Reg.

Name

Bits

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

Reset

0x21 SETUPCON1 [15:8] RESERVED BI_UNIPOLAR1 REFBUF1+ REFBUF1− AINBUF1+ AINBUF1− 0x1000 RW

[7:0] BURNOUT_EN1 RESERVED REF_SEL1 RESERVED

0x22 SETUPCON2 [15:8] RESERVED BI_UNIPOLAR2 REFBUF2+ REFBUF2− AINBUF2+ AINBUF2− 0x1000 RW

[7:0] BURNOUT_EN2 RESERVED REF_SEL2 RESERVED

0x23 SETUPCON3 [15:8] RESERVED BI_UNIPOLAR3 REFBUF3+ REFBUF3− AINBUF3+ AINBUF3− 0x1000 RW

[7:0] BURNOUT_EN3 RESERVED REF_SEL3 RESERVED

AD7172-2 Data Sheet

Rev. A | Page 58 of 60

FILTER CONFIGURATION REGISTER 0

Address: 0x28, Reset: 0x0500, Name: FILTCON0

The filter configuration registers are 16-bit registers that configure the ADC data rate and filter options. Writing to any of these registers

resets any active ADC conversion and restarts converting at the first channel in the sequence.

Table 38. Bit Descriptions for FILTCON0

Bits Bit Name Settings Description Reset Access

15 SINC3_MAP0 If this bit is set, the mapping of the filter register changes to directly program

the decimation rate of the sinc3 filter for Setup 0. All other options are

eliminated. This allows fine tuning of the output data rate and filter notch

for rejection of specific frequencies. The data rate when on a single

channel equals fMOD/(32 × FILTCON0[14:0]).

0x0 RW

[14:12] RESERVED These bits are reserved; set these bits to 0. 0x0 R

11 ENHFILTEN0 This bit enables various postfilters for enhanced 50 Hz and 60 Hz rejection

for Setup 0. The ORDER0 bits must be set to 00 to select the sinc5 + sinc1

filter for this bit to work.

0x0 RW

0 Disabled

1 Enabled

[10:8] ENHFILT0 These bits select between various postfilters for enhanced 50 Hz and 60

Hz rejection for Setup 0.

0x5 RW

010 27 SPS, 47 dB rejection, 36.7 ms settling

011 21.25 SPS, 62 dB rejection, 40 ms settling

101 20 SPS, 86 dB rejection, 50 ms settling

110 16.67 SPS, 92 dB rejection, 60 ms settling

7 RESERVED This bit is reserved; set this bit to 0. 0x0 R

[6:5] ORDER0 These bits control the order of the digital filter that processes the

modulator data for Setup 0.

0x0 RW

00 Sinc5 + sinc1 (default)

11 Sinc3

[4:0] ODR0 These bits control the output data rate of the ADC and, therefore, the

settling time and noise for Setup 0. Rates shown are for the sinc5 + sinc1

filter. See Table 20 to Table 23.

0x0 RW

00000 31,250

00001 31,250

00010 31,250

00011 31,250

00100 31,250

00101 31,250

00110 15,625

00111 10,417

01000 5208

01001 2597

01010 1007

01011

503.8

01100

381

01101 200.3

01110 100.2

01111 59.52

10000 49.68

10001 20.01

10010 16.63

10011 10

10100 5

10101 2.5

10110 1.25

Data Sheet AD7172-2

Rev. A | Page 59 of 60

FILTER CONFIGURATION REGISTER 1 TO FILTER CONFIGURATION REGISTER 3

Address: 0x29, 0x2A, 0x2B, Reset: 0x0500, Name: FILTCON1 to FILTCON3

The remaining three filter configuration registers share the same layout as Filter Configuration Register 0.

Table 39. FILTCON1 to FILTCON3 Register Map

Reg.

Name

Bits

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

Reset

0x29

FILTCON1

[15:8]

SINC3_MAP1

RESERVED

ENHFILTEN1

ENHFILT1

0x0500

[7:0]

RESERVED

ORDER1

ODR1

0x2A

FILTCON2

[15:8]

SINC3_MAP2

RESERVED

ENHFILTEN2

ENHFILT2

0x0500

[7:0]

RESERVED

ORDER2

ODR2

0x2B

FILTCON3

[15:8]

SINC3_MAP3

RESERVED

ENHFILTEN3

ENHFILT3

0x0500

[7:0]

RESERVED

ORDER3

ODR3

OFFSET REGISTER 0

Address: 0x30, Reset: 0x800000, Name: OFFSET0

The offset (zero-scale) registers are 24-bit registers that compensate for any offset error in the ADC or in the system.

Table 40. Bit Descriptions for OFFSET0

Bits Bit Name Settings Description Reset Access

[23:0] OFFSET0 Offset calibration coefficient for Setup 0. 0x800000 RW

OFFSET REGISTER 1 TO OFFSET REGISTER 3

Address: 0x31, 0x 32, 0x33, Reset: 0x800000, Name: OFFSET1 to OFFSET3

The remaining three offset registers share the same layout as Offset Register 0.

Table 41. OFFSET1 to OFFSET3 Register Map

Reg. Name Bits Reset RW

0x31 OFFSET1 [23:0] OFFSET1[23:0] 0x800000 RW

0x32 OFFSET2 [23:0] OFFSET2[23:0] 0x800000 RW

0x33 OFFSET3 [23:0] OFFSET3[23:0] 0x800000 RW

GAIN REGISTER 0

Address: 0x38, Reset: 0x5XXXX0, Name: GAIN0

The gain (full-scale) registers are 24-bit registers that compensate for any gain error in the ADC or in the system.

Table 42. Bit Descriptions for GAIN0

Bits Bit Name Settings Description Reset Access

[23:0] GAIN0 Gain calibration coefficient for Setup 0. 0x5XXXX0 RW

GAIN REGISTER 1 TO GAIN REGISTER 3

Address: 0x39, 0x3A, 0x3B, Reset: 0x5XXXX0, Name: GAIN1 to GAIN3

The remaining three gain registers share the same layout as Gain Register 0.

Table 43. GAIN1 to GAIN3 Register Map

Reg. Name Bits Reset RW

0x39 GAIN1 [23:0] GAIN1[23:0] 0x5XXXX0 RW

0x3A GAIN2 [23:0] GAIN2[23:0] 0x5XXXX0 RW

0x3B GAIN3 [23:0] GAIN3[23:0] 0x5XXXX0 RW

AD7172-2 Data Sheet

Rev. A | Page 60 of 60

OUTLINE DIMENSIONS

24 13

121 6.40 BSC

4.50

4.40

4.30

PIN 1

7.90

7.80

7.70

0.15

0.05

0.30

0.19

0.65

BSC 1.20

MAX

0.20

0.09

0.75

0.60

0.45

8°

0°

SEATING

PLANE

0.10 COPLANARITY

COMPLIANT TO JEDEC STANDARDS MO-153-AD

Figure 75. 24-Lead Thin Shrink Small Outline Package [TSSOP]

(RU-24)

Dimensions shown in millimeters

ORDERING GUIDE

Models1 Temperature Range Package Description Package Option

AD7172-2BRUZ −40°C to +105°C 24-Lead Thin Shrink Small Outline Package [TSSOP] RU-24

AD7172-2BRUZ-RL −40°C to +105°C 24-Lead Thin Shrink Small Outline Package [TSSOP] RU-24

AD7172-2BRUZ-RL7 −40°C to +105°C 24-Lead Thin Shrink Small Outline Package [TSSOP] RU-24

1 Z = RoHS Compliant Part.

registered trademarks are the property of their respective owners.

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