6-Channel, Low Noise, Low Power, 24-/16-Bit

∑-Δ ADC with On-Chip In-Amp and Reference

AD7794/AD7795

Rev. D

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FEATURES

Up to 23 effective bits

RMS noise: 40 nV @ 4.17 Hz, 85 nV @ 16.7 Hz

Current: 400 μA typical

Power-down: 1 μA maximum

Low noise, programmable gain, instrumentation amp

Band gap reference with 4 ppm/°C drift typical

Update rate: 4.17 Hz to 470 Hz

Six differential analog inputs

Internal clock oscillator

Simultaneous 50 Hz/60 Hz rejection

Reference detect

Programmable current sources

On-chip bias voltage generator

Burnout currents

Low-side power switch

Power supply: 2.7 V to 5.25 V

Temperature range:

B grade: –40°C to +105°C

C grade: –40°C to +125°C

Independent interface power supply

24-lead TSSOP

3-wire serial interface

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

Schmitt trigger on SCLK

APPLICATIONS

Temperature measurement

Pressure measurement

Weigh scales

Strain gage transducers

Gas analysis

Industrial process control

Instrumentation

Blood analysis

Smart transmitters

Liquid/gas chromatography

6-digit DVM

GENERAL DESCRIPTION

The AD7794/AD7795 are low power, low noise, complete

analog front ends for high precision measurement applications.

They contain a low noise, 24-/16-bit ∑-Δ ADC with six

differential inputs. The on-chip low noise instrumentation

amplifier means that signals of small amplitude can be

interfaced directly to the ADC.

Each device contains a precision, low noise, low drift internal

band gap reference, and can also accept up to two external

differential references. Other on-chip features include

programmable excitation current sources, burnout currents,

and a bias voltage generator that is used to set the common-

switch can be used to power down bridge sensors between

conversions, minimizing the system’s power consumption. The

AD7794/AD7795 can operate with either an internal clock or

an external clock. The output data rate from each part can vary

from 4.17 Hz to 470 Hz.

Both parts operate with a power supply from 2.7 V to 5.25 V.

The B-grade parts (AD7794 and AD7795) are specified for a

temperature range of −40°C to +105°C while the C-grade part

(AD7794) is specified for a temperature range of −40°C to

+125°C. They consume a current of 400 μA typical and are

housed in a 24-lead TSSOP.

FUNCTIONAL BLOCK DIAGRAM

DOUT/RDY

DIN

SCLK

CS

SERIAL

INTERFACE

AND

LOGIC

CONTROL

Σ-Δ

ADC

AD7794: 24-BIT ADC

AD7795: 16-BIT ADC

AD7794/AD7795

AIN1(+)

AIN1(–)

AIN2(+)

AIN2(–)

AIN3(+)

AIN3(–)

AIN5(+)/IOUT2

AIN5(–)/IOUT1

AIN6(+)/P1

AIN6(–)/P2

GND

MUX

PSW

GND

BAND GAP

REFERENCE

TEMP

SENSOR

CLK

INTERNAL

CLOCK

GND

REFERENCE

DETECT

GND

AIN4(+)/REFIN2(+) REFIN1(+) AIN4(–)/REFIN2(–) REFIN1(–)

IN-AMP

BUF

Figure 1.