8-Channel, 24-Bit, 32 kSPS Simultaneous Sampling ADC

The AD7770 is an 8-channel, simultaneous sampling ADC. Eight full sigma-delta (Σ-Δ) ADCs are on chip. The AD7770 provides a low input current to allow direct sensor connection. Each input channel has a programmable gain stage allowing gains of 1, 2, 4, and 8 to map lower amplitude sensor outputs into the full-scale ADC input range, maximizing the dynamic range of the signal chain. 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 analog supply voltages, respectively for PGAGAIN = 1. The analog inputs can be configured to accept true differential, pseudo differential, or single-ended signals to match different sensor output configurations.

Each channel contains a PGA, an ADC modulator and a sinc3, low latency digital filter. An SRC is provided to allow fine resolution control over the AD7770 ODR. This control can be used in applications where the ODR resolution is required to maintain 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 output interface and SPI control interface. The ADC data output interface is dedicated to transmitting the ADC conversion results from the AD7770 to the processor. The SPI writes to and reads from the AD7770 configuration registers and for the control and reading of data from the SAR ADC. The SPI can also be configured to output the Σ-Δ conversion data.

The AD7770 includes a 12-bit SAR ADC. This ADC can be used for AD7770 diagnostics without having to decommission one of the Σ-Δ ADC channels dedicated to system measurement functions. With the use of an external multiplexer, which can be controlled through the three general-purpose input/output pins (GPIOs), and signal conditioning, the SAR ADC can validate the Σ-Δ ADC measurements in applications where functional safety is required. In addition, the AD7770 SAR ADC includes an internal multiplexer to

sense internal nodes.

The AD7770 contains a 2.5 V reference and reference buffer. The reference has a typical temperature coefficient of 10 ppm/°C.

The AD7770 offers two modes of operation: high resolution mode and low power mode. High resolution mode provides a higher dynamic range while consuming 14.6 mW per channel; low power mode consumes just 4.75 mW per channel at a reduced dynamic range specification.

The specified operating temperature range is −40°C to +105°C, although the device is operational up to +125°C.

Note that throughout this data sheet, certain terms are used to refer to either the multifunction pins or a range of pins. The multi-function pins, such as DCLK0/SDO, are referred to either by the entire pin name or by a single function of the pin, for example, DCLK0, when only that function is relevant. In the case of ranges of pins, AVSSx refers to the following pins: AVSS1A, AVSS1B, AVSS2A, AVSS2B, AVSS3, and AVSS4.

Applications

* Protection relays

* General-purpose data acquisition

* Industrial process control

* 8-channel, 24-bit simultaneous sampling analog-to-digital converter (ADC)

* Single-ended or true differential inputs

* Programmable gain amplifier (PGA) per channel (gains of 1, 2, 4, and 8)

* Low dc input current

* ±4 nA (differential) and ±8 nA (single-ended)

* Up to 32 kSPS output data rate (ODR) per channel

* Programmable ODRs and bandwidth

* Sample rate converter (SRC) for coherent sampling

* Sampling rate resolution up to 15.2 × 10−6 SPS

* Low latency sinc3 filter path

* Adjustable phase synchronization

* Internal 2.5 V reference

* Two power modes optimizing power dissipation and performance: high resolution mode and low power mode