GENERAL DESCRIPTION

The AD7709 is a complete analog front end for low frequency measurement applications. It contains a 16-bit Σ-Δ ADC, selectable reference inputs, three switchable matched excitation current sources, low-side power switches, and a digital I/O port. The 16-bit channel with PGA accepts fully differential, unipolar, and bipolar input signal ranges from 1.024 x REFIN/128 to 1.024 x REFIN. It can be configured as two fully differential input channels or four pseudo-differential input channels. Signals can be converted directly from a transducer without the need for signal conditioning.

FEATURES

16-Bit Σ-Δ ADC

Programmable Gain Front End

Simultaneous 50 Hz and 60 Hz Rejection at 20 Hz Update Rate

VREF Select? Allows Absolute and Ratiometric Measurement Capability

ISOURCE Select?

16-Bit No Missing Codes

13-Bit p-p Resolution @ 20 Hz, 20 mV Range

16-Bit p-p Resolution @ 20 Hz, 2.56 V Range

INTERFACE

3-Wire Serial

SPI?, QSPI?, MICROWIRE?, and DSP Compatible

Schmitt Trigger on SCLK

POWER

Specified for Single 3 V and 5 V Operation

Normal: 1.25 mA Typ @ 3 V

Power-Down: 7 A (32.768 kHz Crystal Running)

ON-CHIP FUNCTIONS

Rail-to-Rail Input Buffer and PGA

Selectable Reference Inputs

3 Switchable, Ratioed Current Sources for VBE Measurements

4-Bit Digital I/O Port

Low-Side Power Switches

APPLICATIONS

Sensor Measurement

Temperature Measurement

Pressure Measurements

Weigh Scales

Portable Instrumentation

4–20 mA Loops