AD7891 Datasheet, PDF (1/20 Pages) Analog Devices – LC2MOS 8-Channel, 12-Bit High Speed Data Acquisition System

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LC²MOS 8-Channel, 12-Bit
High Speed Data Acquisition System
AD7891
FEATURES
Fast 12-Bit ADC with 1.6 ␮s Conversion Time
Eight 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 (85 mW max)
Power-Down Mode (75 ␮W typ)
APPLICATIONS
Data Acquisition Systems
Motor Control
Mobile Communication Base Stations
Instrumentation
GENERAL DESCRIPTION
The AD7891 is an eight-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 ampli-
fier, 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).
The AD7891 provides the option of either a parallel interface 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 which ensures easy inter-
facing 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.
Power dissipation in normal mode is 90 mW typical while in
the standby mode this is reduced to 75 µW typ. The part is
available in a 44-terminal plastic quad flatpack (PQFP) and a
44-lead plastic leaded chip carrier (PLCC).
V_IN1A
V_IN1B
V_IN2A
V_IN2B
V_IN3A
V_IN3B
V_IN4A
V_IN4B
V_IN5A
V_IN5B
V_IN6A
V_IN6B
V_IN7A
V_IN7B
V_IN8A
V_IN8B
FUNCTIONAL BLOCK DIAGRAM
V_DD V_DD
REF OUT/
REF IN
REF GND
AD7891
+2.5V
REFERENCE
STANDBY
M
U
X
TRACK/HOLD
ADDRESS
DECODE
CONTROL LOGIC
12-BIT
ADC
CLOCK
DATA /
CONTROL
LINES
WR CS RD EOC CONVST MODE AGND AGND DGND
PRODUCT HIGHLIGHTS
1. The AD7891 is a complete monolithic 12-bit data acquisition
system combining an eight-channel multiplexer, 12-bit ADC,
+2.5␣ V reference and track/hold amplifier on a single chip.
2. The AD7891-2 features a conversion time of 1.6 µs and an
acquisition time of 0.4␣ µs. 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 µs when using a hardware
convert start and an acquisition time of 0.7 µs 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 that an overvoltage on an unselected channel
does not affect the conversion on a selected channel. The
AD7891-1 can withstand overvoltages of ± 17 V.
REV. A
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
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
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© Analog Devices, Inc., 1998