8-Channel, 24-Bit,
Simultaneous Sampling ADC
AD7779
Data Sheet
the signal chain. The AD7779 accepts VREF from 1 V up to 3.6 V.
The analog inputs accept unipolar (0 V to VREF/GAIN) or true
bipolar ( VREF/GAIN/2 V) analog input signals with 3.3 V or
1.65 V analog supply voltages. The analog inputs can be
configured to accept true differential, pseudo differential, or single-
ended signals to match different sensor output configurations.
FEATURES
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
Each channel contains an ADC modulator and a sinc3, low
latency digital filter. An SRC is provided to allow fine resolution
control over the AD7779 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
AD7779 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 AD7779 to the processor. The SPI interface
is used to write to and read from the AD7779 configuration
registers and for the control and reading of data from the SAR
ADC. The SPI interface can also be configured to output the
Σ-Δ conversion data.
Up to 16 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 µSPS
Low latency sinc3 filter path
Adjustable phase synchronization
Internal 2.5 V reference
Two power modes
High resolution mode
Low power mode
Optimizes power dissipation and performance
Low resolution successive approximation (SAR) ADC for
system and chip diagnostics
Power supply
The AD7779 includes a 12-bit SAR ADC. This ADC can be used
for AD7779 diagnostics without having to decommission one of
the Σ-Δ ADC channels dedicated to system measurement func-
tions. With the use of an external multiplexer, which can be
controlled through the three general-purpose inputs/outputs pins
(GPIOs), and signal conditioning, the SAR ADC can be used to
validate the Σ-Δ ADC measurements in applications where
functional safety is required. In addition, the AD7779 SAR ADC
includes an internal multiplexer to sense internal nodes.
Bipolar ( 1.65 V) or unipolar (3.3 V) supplies
Digital input/output (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
108 dB signal-to-noise ratio (SNR)/dynamic range at 16 kSPS
in high resolution mode
−109 dB total harmonic distortion (THD)
7 ppm integral nonlinearity (INL)
40 µV offset error
The AD7779 contains a 2.5 V reference and reference buffer.
The reference has a typical temperature coefficient of 10 ppm/°C.
0.1% gain error
10 ppm/°C typical temperature coefficient
The AD7779 offers two modes of operation: high resolution
mode and low power mode. High resolution mode provides a
higher dynamic range while consuming 10.75 mW per channel;
low power mode consumes just 3.37 mW per channel at a
reduced dynamic range specification.
APPLICATIONS
Circuit breakers
General-purpose data acquisition
Electroencephalography (EEG)
Industrial process control
The specified operating temperature range is −40°C to +105°C,
although the device is operational up to +125°C.
GENERAL DESCRIPTION
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.
The AD7779 is an 8-channel, simultaneous sampling ADC.
There are eight full Σ-Δ ADCs on chip. The AD7779 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
Rev. A
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