LTC1863L/LTC1867L
10
For more information www.linear.com/LTC1863L
1863l7lfe
Table 2. Channel Configuration (When COM = 1, CH7/COM Pin
Is Used as COMMON)
SD
OS
S1
S0
COM
CHANNEL CONFIGURATION
“+” “–”
10 0 0 1 CH0 CH7/COM
1 0 0 1 1 CH2 CH7/COM
1 0 1 0 1 CH4 CH7/COM
1 0 1 1 1 CH6 CH7/COM
1 1 0 0 1 CH1 CH7/COM
1 1 0 1 1 CH3 CH7/COM
1 1 1 0 1 CH5 CH7/COM
Driving the Analog Inputs
The analog inputs of the LTC1863L/LTC1867L are easy
to drive. Each of the analog inputs can be used as a sin-
gle-ended input relative to the GND pin (CH0-GND, CH1-
GND, etc) or in pairs (CH0 and CH1, CH2 and CH3, CH4
and CH5, CH6 and CH7) for differential inputs. In addi-
tion, CH7 can act as a COM pin for both single-ended
and differential modes if the COM bit in the input word is
high. Regardless of the MUX configuration, the “+” and
“–” inputs are sampled at the same instant. Any unwanted
signal that is common mode to both inputs will be reduced
by the common mode rejection of the sample-and-hold
circuit. The inputs draw only one small current spike
while charging the sample-and-hold capacitors during
the acquire mode. In conversion mode, the analog inputs
draw only a small leakage current. If the source impedance
of the driving circuit is low then the LTC1863L/LTC1867L
inputs can be driven directly. More acquisition time should
be allowed for a higher impedance source.
The following list is a summary of the op amps that are
suitable for driving the LTC1863L/LTC1867L.
1863L7L F01a
CH0
GND
LTC1863L/
LTC1867L
REFCOMP
2000pF
10µF
50Ω
ANALOG
INPUT
1000pF
1863L7L F01b
CH0
CH1
LTC1863L/
LTC1867L
REFCOMP
1000pF
1000pF
10µF
50Ω
50Ω
DIFFERENTIAL
ANALOG
INPUTS
Figure 1a. Optional RC Input Filtering for Single-Ended Input Figure 1b. Optional RC Input Filtering for Differential Inputs
LT
®
1468: 90MHz, 22V/µs 16-bit accurate amplifier
LT1469: Dual LT1468
LT1490A/LT1491A: Dual/quad micropower amplifiers,
50µA/amplifier max, 500µV offset, common mode range
extends 44V above V– independent of V+, 3V, 5V and
±15V supplies.
LT1568: Very low noise, active RC filter building block,
cutoff frequency up to 10MHz, 2.7V to ±5V supplies.
LT1638/LT1639: Dual/quad 1.2MHz, 0.4V/µs amplifiers,
230µA per amplifier, 3V, 5V and ±15V supplies.
LT1881/LT1882: Dual and quad, 200pA bias current, rail-
to-rail output op amps, up to ±15V supplies.
LTC1992-2: Gain of 2 fully differential input/output
amplifier/driver, 2.5mV offset, C
LOAD
stable, 2.7V to ±5V
supplies.
LT1995: 30MHz, 1000V/µs gain selectable amplifier, pin
configurable as a difference amplifier, inverting and non-
inverting amplifier, ±2.5V to ±15V supplies.
LTC6912: Dual programmable gain amplifiers with SPI
serial interface, 2mV offset, 2.7V to ±5V supplies.
LTC6915: Zero drift, instrumentation amplifier with SPI
programmable gain, 125dB CMRR, 0.1% gain accuracy,
10µV offset.
Input Filtering
The noise and the distortion of the input amplifier and
other circuitry must be considered since they will add
to the LTC1863L/LTC1867L noise and distortion. Noisy
input circuitry should be filtered prior to the analog inputs
to minimize noise. A simple 1-pole RC filter is sufficient
APPLICATIONS INFORMATION