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