Analog Devices Inc.

The AD7770 is an 8-channel, simultaneous sampling ADC. Eightfull sigma-delta (?-?) ADCs are on chip. The AD7770 providesa low input current to allow direct sensor connection. Each inputchannel has a programmable gain stage allowing gains of 1, 2, 4,and 8 to map lower amplitude sensor outputs into the full-scaleADC input range, maximizing the dynamic range of the signalchain. The AD7770 accepts a VREF voltage from 1 V up to 3.6 V.The analog inputs accept unipolar (0 V to VREF) or true bipolar(?VREF/2) analog input signals with 3.3 V or ?1.65 V analogsupply voltages, respectively for PGAGAIN = 1. The analog inputscan be configured to accept true differential, pseudo differential,or single-ended signals to match different sensor outputconfigurations.Each channel contains a PGA, an ADC modulator and asinc3, low latency digital filter. An SRC is provided to allow fineresolution control over the AD7770 ODR. This control can beused in applications where the ODR resolution is required tomaintain coherency with 0.01 Hz changes in the line frequency.The SRC is programmable through the serial port interface (SPI).The AD7770 implements two different interfaces: a data outputinterface and SPI control interface. The ADC data output interfaceis dedicated to transmitting the ADC conversion results fromthe AD7770 to the processor. The SPI writes to and reads fromthe AD7770 configuration registers and for the control andreading of data from the SAR ADC. The SPI can also beconfigured to output the ?-? conversion data.The AD7770 includes a 12-bit SAR ADC. This ADC can beused for AD7770 diagnostics without having to decommissionone of the ?-? ADC channels dedicated to system measurementfunctions. With the use of an external multiplexer, which can becontrolled through the three general-purpose input/output pins(GPIOs), and signal conditioning, the SAR ADC can validatethe ?-? ADC measurements in applications where functionalsafety is required. In addition, the AD7770 SAR ADC includesan internal multiplexer to sense internal nodes.The AD7770 contains a 2.5 V reference and reference buffer. Thereference has a typical temperature coefficient of 10 ppm/?C.The AD7770 offers two modes of operation: high resolution modeand low power mode. High resolution mode provides a higherdynamic range while consuming 10.75 mW per channel; lowpower mode consumes just 3.37 mW per channel at a reduceddynamic range specification.The specified operating temperature range is ?40?C to +105?C,although the device is operational up to +125?C.Applications Protection relays General-purpose data acquisition Industrial process control

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