AD7771_17 Datasheet, PDF (1/99 Pages) Analog Devices – 8-Channel, 24-Bit, Simultaneous Sampling ADC

Data Sheet
FEATURES
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)
−109 dB THD
±8 ppm of FSR INL
±15 µV offset error
±0.1% FS gain error
±10 ppm/°C typical temperature coefficient
APPLICATIONS
Power quality and measurement applications
General-purpose data acquisition
Electroencephalography (EEG)
Industrial process control
GENERAL DESCRIPTION
The AD7771¹ 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
1 _{This product is protected by at least U.S. Patent No. 9.432,043.}
Rev. 0
Document Feedback
Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other
rights of third parties that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarks and registered trademarks are the property of their respective owners.
8-Channel, 24-Bit,
Simultaneous Sampling ADC
AD7771
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 trans-
mitting 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 func-
tions. 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.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: [phone]
©2017 Analog Devices, Inc. All rights reserved.
Technical Support
www.analog.com