AD7770_17 Datasheet, PDF (1/98 Pages) Analog Devices – 8-Channel, 24-Bit, Simultaneous Sampling ADC

Data Sheet
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 (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
Low resolution successive approximation register (SAR) ADC
for system and chip diagnostics
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
103 dB dynamic range at 32 kSPS in high resolution mode
−109 dB total harmonic distortion (THD)
±9 ppm of FSR integral nonlinearity (INL)
±15 µV offset error
±0.1% FS gain error
±10 ppm/°C typical temperature coefficient
APPLICATIONS
Protection relays
General-purpose data acquisition
Industrial process control
GENERAL DESCRIPTION
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.
Rev. C
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8-Channel, 24-Bit,
Simultaneous Sampling ADC
AD7770
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 10.75 mW per channel; low
power mode consumes just 3.37 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.
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