Low Power, 16-/24-Bit Sigma-Delta ADC

for Bridge Sensors

AD7796/AD7797

Rev. A

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FEATURES

RMS noise: 65 nV

Instrumentation amp

Temperature sensor

Internal clock oscillator

Simultaneous 50 Hz/60 Hz rejection

Update rate: 4.17 Hz to 123 Hz

Current: 250 μA typ

Power-down: 1 μA

Power supply: 2.7 V to 5.25 V

–40°C to +85°C temperature range

Independent interface power supply

16-lead TSSOP

INTERFACE

3-wire serial

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

Schmitt trigger on SCLK

APPLICATIONS

Weigh scales

Strain gages

Industrial process control

Instrumentation

Portable instrumentation

GENERAL DESCRIPTION

The AD7796/AD7797 are complete, analog front ends for high

precision, bridge sensor applications such as weigh scales. The

AD7796/AD7797 contain a Σ-Δ ADC capable of 16-/24-bit

resolution, respectively. The on-chip instrumentation amplifier

has a fixed gain of 128, allowing small amplitude signals such as

those from bridge sensors to be directly interfaced to the ADC.

Each part has one differential input and contains a temperature

sensor that is internally connected to the ADC. This sensor can

be used to perform temperature compensation of the bridge.

The devices can be operated with the internal clock or an

external clock. The output data rate from the parts is software-

programmable and can be varied from 4.17 Hz to 123 Hz.

The AD7796/AD7797 operate with a power supply from 2.7 V

to 5.25 V. Each part consumes a current of 250 μA typical and is

housed in a 16-lead TSSOP.

FUNCTIONAL BLOCK DIAGRAM

AD7796/

AD7797

DOUT/RDY

DIN

SCLK

AIN(+)

AIN(–)

MUX

GND

Σ-Δ

ADC

×128

REFERENCE

TEMP

SENSOR

INTERNAL

CLOCK

REFIN(–)

REFIN(+)

CLK

AD7796: 16-BIT ADC

AD7797: 24-BIT ADC

SERIAL

INTERFACE

AND

CONTROL

LOGIC

CS

Figure 1.