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LTC1867LACGN

Micropower, 3V, 12-/16-Bit, 8-Channel 175ksps ADCs

Linear Technology 

LTC1863L/LTC1867L

APPLICATIONS INFORMATION

Table 2. Channel Configuration (When COM = 1, CH7/COM Pin

Is Used as COMMON)

CHANNEL CONFIGURATION

SD OS S1 S0 COM

“+”

“–”

1

0

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

single-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

addition, 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. More de-

tailed information is available in the Linear Technology

data books or Linear Technology website.

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 am-

plifier/driver, 2.5mV offset, CLOAD 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 for

ANALOG

50Ω

INPUT

2000pF

CH0

LTC1863L/

LTC1867L

GND

10µF

REFCOMP

1863L7L F01a

50Ω

DIFFERENTIAL

ANALOG

INPUTS

50Ω

1000pF

1000pF

1000pF

CH0

LTC1863L/

LTC1867L

CH1

10µF

REFCOMP

1863L7L F01b

Figure 1a. Optional RC Input Filtering for Single-Ended Input

Figure 1b. Optional RC Input Filtering for Differential Inputs

1863l7lfd

10

For more information www.linear.com/LTC1863L

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