The AD7771 is an 8-channel, simultaneous sampling analog-to-digital converter (ADC). Eight full Σ-Δ ADCs are on-chip. The AD7771 provides an ultralow 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 AD7771 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 V) analog input signals with 3.3 V or ±1.65 V analog supply voltages, respectively. The analog inputs can be configured to accept true differential or single-ended signals to match different sensor output configurations.
Each channel contains an ADC modulator and a sinc3/sinc5, low latency digital filter. A sample rate converter (SRC) is provided to allow fine resolution control over the AD7771 output data rate (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 AD7771 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 AD7771 to the processor. The SPI writes to and reads from the AD7771 configuration registers and for the control and reading of data from the successive approximation register (SAR) ADC. The SPI can also be configured to output the Σ-Δ conversion data.
The AD7771 includes a 12-bit SAR ADC. This ADC can be used for AD7771 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 AD7771 SAR ADC includes an internal multiplexer to sense internal nodes.
The AD7771 contains a 2.5 V reference and reference buffer. The reference has a typical temperature coefficient of ±10 ppm/°C.
The AD7771 offers two modes of operation: high resolution mode and low power mode. High resolution mode provides a higher dynamic range while consuming 16.6 mW per channel; low power mode consumes only 5.25 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 multifunction 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**
Power quality and measurement applications
General-purpose data acquisition
Electroencephalography (EEG)
Industrial process control
### Features and Benefits
8-channel, 24-bit simultaneous sampling ADC
Single-ended or true differential inputs
PGA per channel (gains of 1, 2, 4, and 8)
Low dc input current
±4 nA (differential)/±8 nA (single-ended)
Up to 128 kSPS ODR per channel
Programmable ODRs and bandwidth
SRC for coherent sampling
Sampling rate resolution up to 15.2 × 10−6 SPS
Low latency sinc3 and sinc5 filter paths
Adjustable phase synchronization
Internal 2.5 V reference
Two power modes
High resolution mode
Low power mode
Optimizes power dissipation and performance
Low resolution SAR ADC for system and chip diagnostics
Power supply
Bipolar (±1.65 V) or unipolar (3.3 V) supplies
Digital I/O supply: 1.8 V to 3.6 V
Performance temperature range: −40°C to +105°C
Functional temperature range: −40°C to +125°C
Performance
Combined ac and dc performance
107 dB SNR/dynamic range at 32 kSPS in high resolution mode (sinc5)
