FEATURES

AD7705: 2 fully differential input channel ADCs

AD7706: 3 pseudo differential input channel ADCs

16 bits no missing codes

0.003% nonlinearity

Programmable gain front end: gains from 1 to 128

3-wire serial interface

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

Schmitt-trigger input on SCLK

Ability to buffer the analog input

2.7 V to 3.3 V or 4.75 V to 5.25 V operation

Power dissipation 1 mW maximum @ 3 V

Standby current 8 μA maximum

16-lead PDIP, 16-lead SOIC, and 16-lead TSSOP packages

GENERAL DESCRIPTION

The AD7705/AD7706 are complete analog front ends for low

frequency measurement applications. These 2-/3-channel devices

can accept low level input signals directly from a transducer and

produce serial digital output. The devices employ a Σ-Δ

conversion technique to realize up to 16 bits of no missing codes

performance. The selected input signal is applied to a

proprietary, programmable-gain front end based around an

analog modulator. The modulator output is processed by an onchip digital filter. The first notch of this digital filter can be programmed via an on-chip control register, allowing adjustment of

the filter cutoff and output update rate.

The AD7705/AD7706 devices operate from a single 2.7 V to

3.3 V or 4.75 V to 5.25 V supply. The AD7705 features two fully

differential analog input channels; the AD7706 features three

pseudo differential input channels.

Both devices feature a differential reference input. Input signal

ranges of 0 mV to 20 mV through 0 V to 2.5 V can be

incorporated on both devices when operating with a VDD of 5 V

and a reference of 2.5 V. They can also handle bipolar input

signal ranges of ±20 mV through ±2.5 V, which are referenced to

the AIN(−) inputs on the AD7705 and to the COMMON input

on the AD7706.