8-Channel, 24-Bit,
Simultaneous Sampling ADC
AD7779
Data Sheet
dynamic range of the signal chain. The AD7779 accepts VREF
from 1 V up to 3.6 V. The analog inputs accept unipolar (0 V to
V
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)
REF) 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.
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 trans-
mitting 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
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 as an internal multiplexer to sense internal nodes.
Power supply
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
The AD7779 contains a 2.5 V reference and reference buffer. The
reference has a typical temperature coefficient of 10 ppm/°C.
−109 dB total harmonic distortion (THD)
7 ppm integral nonlinearity (INL)
40 μV offset error
0.1ꢀ 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
The specified operating temperature range is −40°C to +105°C,
although the device is operational up to +125°C.
General-purpose data acquisition
Electroencephalography (EEG)
Industrial process control
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.
GENERAL DESCRIPTION
The AD7779 is an 8-channel, simultaneous sampling ADC. There
are eight full sigma-delta (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
Rev. 0
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