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
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