3-Channel, Low Noise, Low Power,

Data Sheet

AD7798/AD7799

Rev. B

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FEATURES

RMS noise:

27 nV at 4.17 Hz (AD7799)

65 nV at 16.7 Hz (AD7799)

40 nV at 4.17 Hz (AD7798)

85 nV at 16.7 Hz (AD7798)

Current: 380 µA typical

Power-down: 1 µA maximum

Low noise, programmable gain, instrumentation amp

Update rate: 4.17 Hz to 470 Hz

3 differential inputs

Internal clock oscillator

Simultaneous 50 Hz/60 Hz rejection

Reference detect

Low-side power switch

Programmable digital outputs

Burnout currents

Power supply: 2.7 V to 5.25 V

–40°C to +105°C temperature range

Independent interface power supply

16-lead TSSOP package

INTERFACE

3-wire serial

SPI®, QSPI™, MICROWIRE™, and DSP compatible

Schmitt trigger on SCLK

APPLICATIONS

Weigh scales

Pressure measurement

Strain gauge transducers

Gas analysis

Industrial process control

Instrumentation

Portable instrumentation

Blood analysis

Smart transmitters

Liquid/gas chromotography

6-digit DVM

FUNCTIONAL BLOCK DIAGRAM

DOUT/RDY

DIN

SCLK

CS

SERIAL

INTERFACE

AND

CONTROL

LOGIC

Σ-Δ

ADC

AD7798/AD7799

AD7798: 16-BIT

AD7799: 24-BIT

AIN2(+)

AIN2(–)

AIN3(+)/P1

AIN1(+)

AIN1(–)

AIN3(–)/P2

GND

MUX

INTERNAL

CLOCK

GND

GND

REFIN(–)

PSW

IN-AMP

REFERENCE

DETECT

REFIN(+)

Figure 1.

GENERAL DESCRIPTION

The AD7798/AD7799 are low power, low noise, complete

analog front ends for high precision measurement applications.

The AD7798/AD7799 contains a low noise, 16-/24-bit ∑-∆

ADC with three differential analog inputs. The on-chip, low

noise instrumentation amplifier means that signals of small

amplitude can be interfaced directly to the ADC. With a gain

setting of 64, the rms noise is 27 nV for the AD7799 and 40 nV

for the AD7798 when the update rate equals 4.17 Hz.

On-chip features include a low-side power switch, reference

detect, programmable digital output pins, burnout currents,

and an internal clock oscillator. The output data rate from the

part is software-programmable and can be varied from 4.17 Hz

to 470 Hz.

The part operates with a power supply from 2.7 V to 5.25 V.

The AD7798 consumes a current of 300 µA typical, whereas the

AD7799 consumes 380 µA typical. Both devices are housed in a

16-lead TSSOP package.