September 1996 - Linear Technology

Linear Technology Chronicle •

September 1996

A Showcase of Linear Technology’s Focus Products

Linear Technology Chronicle

September 1996 Vol. 5 No. 9

Products of the Month

, LTC and LT are registered trademarks of Linear Technology Corporation.

Micropower 8-Channel 12-Bit ADCs with MUX

Offer ±0.75LSB Max DNL

Adaptive Frequency

Boost Converters

Provide Low Noise and

High Efficiency Over a

Wide Range of Loads

The LT

1500/LT1501 are low noise

micropower DC/DC converters for battery

applications using two or more cells or a

supplied voltage of 1.8V minimum. The

current mode architecture monitors the

switch current to produce a well controlled

peak switch and battery current. These high

efficiency converters provide low noise 5V

to 12V conversion at 200mA or can deliver

300mA at 3.3V from just two cells (2V

minimum). Operating quiescent current is

just 200µA and only 8µA (typ) in shutdown.

They are capable of operating with supply

voltages from 1.8V to 15V. The LT1500/

LT1501 are ideal for communications appli-

cations, such as wireless modems, which

require good efficiency and fairly constant

frequency operation with low switching

noise over a wide range of load currents.

The LT1500 requires only four external

surface mount components to implement a

current mode boost converter—input and

output capacitors, an inductor and a diode.

The switching frequency is determined by

the input and output voltages and inductor

value, so it will vary somewhat as the input

voltage changes. In contrast to pulse skip-

ping switching regulators, the current mode

operation of the LT1500/LT1501 causes the

operating frequency to linearly increase as

the load current decreases. This keeps the

switching frequency out of the audio band

at most load currents. The LT1500 has an

advantage over other variable frequency

methods which can cause the switching

frequency to vary into the audio range.

World’s Only Dual, Micropower, C-LoadTM JFET Op Amps .................................................... 2

Driving the Analog Input of High Performance A/D Converters .............................................. 3

New Data Conversion Solutions Brochure ............................................................................. 4

SwitcherCADTM Update............................................................................................................ 4

Inside This Issue:

The LTC

1598/LTC1598L are 8-chan-

nel multiplexed 12-bit micropower ADCs

for single 5V and 3V supply applications.

The 5V LTC1598 typically draws just

320µA at 16.8ksps sampling rates while the

3V LTC1598L draws only 250µA at

10.5ksps. Both save power by automatically

powering down to a mere 1nA when not

converting. Each has an 8-channel high

impedance input and are packaged in a

24-pin SSOP. Maximum differential linear-

ity error of ±0.75LSB guarantees a true

12-bit no-missing codes resolution. They are

ideal for such space conscious, power sensi-

tive applications as pen screen interface,

remote process control, battery monitoring

and portable data acquisition.

These ADCs have a multiplexer output

that is separate from the ADC input, allow-

ing one signal conditioning circuit for all

channels. This improves channel matching

characteristics and reduces component

count. For example, a filter can be imple-

mented once and used for all four channels.

Separate control of the multiplexer and ADC

allows continuous sampling of a single chan-

nel without addressing prior to each

conversion.

The 3-wire serial interface reduces I/O

lines in remote or isolated applications. All

devices are SPI, QSPI and MICROWIRE

compatible. The LTC1598/LTC1598L are

screened to the commercial and industrial

temperature ranges. Contact your local

Linear Technology sales office for data

sheets and evaluation samples.

C-Load and SwitcherCAD are trademarks of Linear Technology Corporation.

ANALOG

INPUTS

0V TO 5V

RANGE

1k 1µF

LTC1598 • TA01

OPTIONAL 

ADC FILTER

CH0

CH1

CH2

CH3

CH4

CH5

CH6

CH7

20

21

22

23

24

1

2

–

8-CHANNEL

MUX

8 COM GND

4, 9

MPU

SERIAL DATA LINK

MICROWIRE AND

SPI COMPATABLE

10

6

5, 14

7

CS ADC

CS MUX

CLK



OUT

12

NC

12-BIT

SAMPLING

ADC

ADCINMUXOUT

18 17 16 15, 19 1µF

REF

Figure 1. LTC1598 24µW, 8-Channel, 12-Bit ADC Samples at 200Hz

and Runs Off a 5V Supply

MICROWIRE is a trademark of National Semiconductor Corp.

Continued on page 2

Linear Technology Chronicle •

September 1996

LT1500/LT1501 from page 1

Figure 1. LT1501 Used as a 2-Cell to 5V Converter

SHDN

LBO

LBI

SENSE

GND

OUT

LT1501-5

1nF

301k

LOW-BATTERY FLAG

(USE EXTERNAL PULL-UP)

33µF*

220µF**

10V

TANT

2 EACH

NiCd OR

ALKALINE

CELLS

22µH

†

5V, 200mA

LT1500/01 • TA01

AVX, TPSC107M006R0150

AVX, TPSD107M010 R0100

SUMIDA CD73-220, CD54-220

OR CD43-220. SELECT ACCORDING

TO MAXIMUM LOAD CURRENT

*

**

†

The LT1500 is offered in a 14-lead SO

package with two options available for fixed

output (3.3V or 5V) or adjustable operation

and includes a synchronization function. The

LT1501 is in an 8-lead SO package and is

not synchronizable. Both devices include a

low-battery detector which is alive in shut-

down. Contact your local Linear Technology

sales office for a data sheet and evaluation

samples.

World’s Only Dual,

Micropower, C-Load,

JFET Op Amps

The LT1462 and LT1464 are dual

JFET input amplifiers that consume only

45µA and 200µA of supply current per

amplifier, respectively. The LT1462 has a

slew rate of 0.13V/µs and 175kHz band-

width. The LT1464 has a slew rate of

0.9V/µs and 1MHz bandwidth. These low

power JFET amplifiers offer tremendous

–

1/4 LTC201

7R1*

1/2 LT1464

–

1/2 LT1464

–

C1 

10nF

POLYSTYRENE

OUT

 TYPICAL DROOP = = 0.05mV/s

 TOTAL SUPPLY CURRENT = 460 µA MAX

*R1 = 600 Ω FOR ±15V SUPPLIES

 R1 = 0 Ω FOR ±5V SUPPLIES

0.5pA

10nF

LT1464 • TA01

FUNCTION MODE IN A IN B MODE IN A IN B

Track-and-Hold Track 0 0 Hold 1 1

Positive Peak Detector Reset 0 0 Store 0 1

Negative Peak Detector Reset 0 0 Store 1 0

LTC201 switch is open for logic "1."

MCT2

power savings—extending battery life and

maintaining low bias currents by running

cooler than other JFETs. They are ideally

suited for battery-powered systems, photo

current amplifiers and as low frequency,

micropower active filters.

The LT1462 and LT1464 are

micropower op amps that draw only 45µA

and 200µA max respectively, yet they are

still capable of driving large capacitive

loads. Both of these C-Load stable op amps

require just picoamperes of input bias cur-

rent (0.5pA typical) and are unity-gain stable

for capacitive loads up to 10,000pF. Their

outputs can swing a 10k load to within 1.5V

of either supply while their input common

mode range can swing to and include the

positive rail.

The LT1462 and the LT1464 are

offered in standard 8-pin DIP and SO

packages. The quad versions, LT1463

and LT1465, will soon join this family of

micropower JFET amplifiers. Contact your

local Linear Technology sales office for data

sheets and evaluation samples.

Figure 1. LT1464 JFET Input Op Amp as a Micropower Low

Droop Track-and-Hold/Peak Detector

= 1

= ±5V, ±15V

= 10nF

1464 TA02

Figure 2. Small-Signal Response, CLOAD = 10nF

Linear Technology Chronicle •

September 1996

Application of the Month

Driving the Analog Input of High Performance A/D Converters

The inputs to switched capacitor

ADCs are easy to drive if you allow for the

fact that they draw a small input current

transient at the end of each conversion.

This happens when the internal sampling

capacitors switch back onto the input to

acquire the next sample. For accurate re-

sults, the circuitry driving the analog input

must settle from this transient before the

next conversion is started.

There are two ways to accomplish

this. One is to drive the ADC with an op

amp that settles from a load transient in

less than the acquisition time of the ADC.

Fortunately, most op amps settle much

more quickly from a load transient than

from an input step, so meeting this require-

ment is not too difﬁcult. The LT1363, for

example, is a good choice for driving the

LTC1410 input.

A second solution to handling the input

transient is to use an input RC ﬁlter with a

capacitor much larger than the ADC input

capacitance. This larger capacitor provides

the charge for the sampling capacitor, which

eliminates the voltage transient altogether.

Figure 1 shows such a ﬁlter for the

LTC1410. The 1000pF capacitor provides

the input charge for the ADC’s sampling

capacitor. The LT1363’s capacitive load

driving capability makes it a good choice for

use with this ﬁlter.

Filter Wideband Noise

from the Input Signal

Many new converters have wide S/H input

bandwidths. This is great for capturing high

frequency input signals, but for lower input

bandwidth applications the converter will

pick up any wideband noise that may be in

the input signal. To avoid this, use a ﬁlter

at the ADC input to pass only your desired

signal bandwidth.

The simple ﬁlter in Figure 1

bandlimits the input signal to 3MHz and

still allows clean sampling up to the

Nyquist frequency (625kHz). Figure 2

shows the Nyquist performance of the

LTC1410 using this ﬁlter. The signal to

noise and distortion ratio (SINAD) is

71.5dB and total harmonic distortion

(THD) is –84dB.



SAMPLE

= 1.25Msps WITH NO JITTER

= 600kHz

SINAD = 71.5dB

INPUT FREQUENCY (Hz)

–120

–100

–80

–60

–40

–20

AMPLITUDE (dB)

0K 100K 200K 500K 600K400K300K

ADC_04.eps

–

±2.5V

INPUT 50Ω

20MHz

S/H ADC

LTC1410

1000pF

–

AGND

LT1363

Figure 1. Many New ADCs Have Wide Bandwidth Sample-and-Holds.

In Lower Bandwidth Applications, a Simple RC Filter Will Remove

Wideband Noise That May Be Present in the Signal

Figure 2. With a Low Jitter Source, the LTC1410 Will Give

71.5dB SINAD When Sampling a Nyquist Input Signal

Linear Technology Chronicle •

September 1996

Linear Technology Corporation • 1630 McCarthy Blvd. • Milpitas, California 95035-7417 • (408) 432-1900 • FAX: (408) 434-0507 • For Literature Only: 1-800-4-LINEAR

Linear Technology

Products Are

Distributed By:

Almac/Arrow

Arrow/Schweber

Arrow/Zeus

Digi-Key

Electrosonic

Gerber Electronics

Farnell Electronics

Marshall Industries

Phase 1

New Data Conversion

Solutions Brochure

The 1996 Data Conversion Solutions

brochure has just been published and is

now available. This 52 page booklet con-

tains practical tips on how to apply LTC’s

growing line of data conversion products,

namely our A/D converters and DACs as

well as multiplexer/switches and referenc-

es. Each product section cross-references

the entire product line, highlights new prod-

ucts for the year and then describes various

applications of individual devices, complete

with schematic and a description on how

the circuit works.

The Analog-to-Digital Converter sec-

tion has tables that list the entire product

line in descending sample rates, starting

with the 1.25Msps LTC1410 and ending

with low power converters under 10ksps.

Other tables break out the A/D product line

in terms of output (parallel or serial),

micropower, 3V supply and those devices

offered in the popular SO-8 package. This

is then followed by several new product

cameos where features of recently intro-

duced products are presented along with a

block diagram.

The heart of each section is the appli-

cation notes, where practical design

examples are described along with a sche-

matic. There are 60 products described and

24 application notes for you to review.

Additional application notes and design

notes on data conversion solutions are also

referenced. The brochure concludes with a

glossary of terms, including frequently used

abbreviations. To receive a copy, contact

your local Linear Technology sales office.

LINEAR TECHNOLOGY

CORPORATION



1996 DATA CONVERSION

SOLUTIONS

First Edition

CH0

CH1

GND

SPI, QSPI

MICROWIRETM

I/O

5V20µA

100µW SO-8 12-Bit ADC

LTC1298

Lowest Power 4-Channel 12-Bit ADC

SPI, QSPI

MICROWIRETM

I/O

BATT

TEMP

PEN

SCREEN LTC1594

SO-16



AMPLITUDE (dB)

FREQUENCY (kHz)

0

–20

–40

–60

–80

–100

–120 100 200 300 400 500 600

SAMPLE

= 1.25MHz

= 599.975kHz

SFDR = 84.7dB

SINAD = 71.7dB

Best 1.25Msps 12-Bit ADC

= 1.25Msps

= 625kHz

12-BIT

DAC

3-WIRE

SERIAL I/O

REF

CLK

OUT

POWER-ON

RESET

–

CS/LD

Micropower Rail-to-Rail V

OUT

DAC

RAIL-TO-RAIL

VOLTAGE

OUTPUT

12-BIT

SHIFT

REG

AND

DAC

LATCH

SO-8

LTC1451: 5V

LTC1452: 3V TO 5V

LTC1453: 3V

Fastest 12-Bit ADC in SO-8

SO-8

LTC1410

REF OUT

INPUT

GND

HIGH SPEED

SERIAL I/O

5V –5V fS = 400ksps

fIN = 200kHz

SO-8

LTC1400

First Edition of 1996 Data Conversion

Solutions Brochure Is Now Available

SwitcherCAD Update

New software for automated power man-

agement designs now supports high

frequency DC/DC converters.

A new version of SwitcherCAD is now

available for designing high frequency dis-

tributed power control circuits.

SwitcherCAD accepts inputs for power

supply requirements and returns the circuit

topology, such as the external component

values and the power ICs required to imple-

ment a design. Included in the component

data base are new high frequency PWM

switchers, such as the LT137X family, as

well as new surface mount components

(coils, capacitors and diodes) required for

high frequency PWM operation.

The program disk runs on IBM or com-

patible computers and is available on a

3.5-inch floppy disk. SwitcherCAD is sup-

plied with a 6-chapter user’s manual which

includes instructions on how to input data

fields and what formulas to use. Vendor

sources for purchasing external components

are also provided.

The new converter IC data base now

includes the 500kHz step-down converters

LT1375, LT1376, LT1507 and 250kHz to

1MHz boost converters LT1371, LT1372,

LT1373 and LT1377. The original LT107X,

LT117X, LT127X and LT1082 converter

families are also in the data base.

SwitcherCAD Version 2.18 is available

free of charge from your local LTC sales

representative.