a
LC2MOS 8-Channel, 12-Bit
High Speed Data Acquisition System
AD7891
FEATURES
Fast 12-Bit ADC with 1.6 s Conversion Time
8 Single-Ended Analog Input Channels
Overvoltage Protection on Each Channel
Selection of Input Ranges:
؎5 V, ؎10 V for AD7891-1
0 to +2.5 V, 0 to +5 V, ؎2.5 V for AD7891-2
Parallel and Serial Interface
On-Chip Track/Hold Amplifier
On-Chip Reference
Single-Supply, Low Power Operation (100 mW Max)
Power-Down Mode (75 W Typ)
APPLICATIONS
Data Acquisition Systems
Motor Control
Mobile Communication Base Stations
Instrumentation
FUNCTIONAL BLOCK DIAGRAM
VDD VDD
VIN1A
VIN1B
VIN2A
VIN2B
VIN3A
VIN3B
VIN4A
VIN4B
VIN5A
VIN5B
VIN6A
VIN6B
VIN7A
VIN7B
VIN8A
VIN8B
REF OUT/
REF IN
REF GND
2.5V
REFERENCE
STANDBY
AD7891
12-BIT
ADC
M
U
X
TRACK/HOLD
DATA/
CONTROL
LINES
ADDRESS
DECODE
CLOCK
CONTROL LOGIC
WR CS RD EOC CONVST MODE
AGND AGND DGND
GENERAL DESCRIPTION
PRODUCT HIGHLIGHTS
The AD7891 is an 8-channel, 12-bit data acquisition system
with a choice of either parallel or serial interface structure. The
part contains an input multiplexer, an on-chip track/hold amplifier, a high speed 12-bit ADC, a 2.5 V reference, and a high
speed interface. The part operates from a single 5 V supply and
accepts a variety of analog input ranges across two models, the
AD7891-1 (± 5 V and ± 10 V) and the AD7891-2 (0 V to +2.5 V,
0 V to +5 V, and ± 2.5 V).
1. The AD7891 is a complete monolithic 12-bit data acquisition
system that combines an 8-channel multiplexer, 12-bit ADC,
2.5 V reference, and track/hold amplifier on a single chip.
The AD7891 provides the option of either a parallel or serial
interface structure determined by the MODE pin. The part
has standard control inputs and fast data access times for both
the serial and parallel interfaces, ensuring easy interfacing to
modern microprocessors, microcontrollers, and digital signal
processors.
In addition to the traditional dc accuracy specifications, such as
linearity, full-scale and offset errors, the part is also specified for
dynamic performance parameters, including harmonic distortion
and signal-to-noise ratio.
2. The AD7891-2 features a conversion time of 1.6 ms and an
acquisition time of 0.4 ms. This allows a sample rate of
500 kSPS when sampling one channel and 62.5 kSPS when
channel hopping. These sample rates can be achieved using
either a software or hardware convert start. The AD7891-1
has an acquisition time of 0.6 ms when using a hardware
convert start and an acquisition time of 0.7 ms when using a
software convert start. These acquisition times allow sample
rates of 454.5 kSPS and 435 kSPS, respectively, for hardware
and software convert start.
3. Each channel on the AD7891 has overvoltage protection. This
means an overvoltage on an unselected channel does not affect
the conversion on a selected channel. The AD7891-1 can
withstand overvoltages of ± 17 V.
Power dissipation in normal mode is 82 mW typical; in
the standby mode, this is reduced to 75 mW typ. The part is
available in a 44-terminal MQFP and a 44-lead PLCC.
REV. D
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. 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.
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Tel: 781/329-4700
www.analog.com
Fax: 781/326-8703
© 2004 Analog Devices, Inc. All rights reserved.
