AD7890 Datasheet, PDF (1/20 Pages) Analog Devices – LC2MOS 8-Channel, 12-Bit Serial, Data Acquisition System

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LC²MOS 8-Channel, 12-Bit
Serial, Data Acquisition System
AD7890
FEATURES
Fast 12-Bit ADC with 5.9 ␮s Conversion Time
Eight Single-Ended Analog Input Channels
Selection of Input Ranges:
؎10 V for AD7890-10
0 V to ؉4.096 V for AD7890-4
0 V to ؉2.5 V for AD7890-2
Allows Separate Access to Multiplexer and ADC
On-Chip Track/Hold Amplifier
On-Chip Reference
High Speed, Flexible, Serial Interface
Single Supply, Low Power Operation (50 mW max)
Power-Down Mode (75 ␮W typ)
GENERAL DESCRIPTION
The AD7890 is an eight-channel 12-bit data acquisition system.
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, serial interface. The part operates from a single +5 V supply
and accepts an analog input range of ±10 V (AD7890-10), 0 V to
+4.096 V (AD7890-4) and 0 V to +2.5 V (AD7890-2).
The multiplexer on the part is independently accessible. This
allows the user to insert an antialiasing filter or signal condition-
ing, if required, between the multiplexer and the ADC. This
means that one antialiasing filter can be used for all eight chan-
nels. Connection of an external capacitor allows the user to
adjust the time given to the multiplexer settling to include any
external delays in the filter or signal conditioning circuitry.
Output data from the AD7890 is provided via a high speed bidi-
rectional serial interface port. The part contains an on-chip con-
trol register, allowing control of channel selection, conversion
start and power-down via the serial port. Versatile, high speed
logic ensures easy interfacing to serial ports on microcontrollers
and digital signal processors.
In addition to the traditional dc accuracy specifications such as
linearity, full-scale and offset errors, the AD7890 is also speci-
fied for dynamic performance parameters including harmonic
distortion and signal-to-noise ratio.
FUNCTIONAL BLOCK DIAGRAM
MUX SHA REF OUT/
V_DD
OUT IN REF IN
V_IN1
V_IN2
V_IN3
V_IN4
V_IN5
V_IN6
V_IN7
V_IN8
SIGNAL
SCALING*
SIGNAL
SCALING*
SIGNAL
SCALING*
SIGNAL
SCALING*
SIGNAL
SCALING*
SIGNAL
SCALING*
SIGNAL
SCALING*
SIGNAL
SCALING*
2kΩ
+2.5V
REFERENCE
AD7890
M
U
X
12-BIT
ADC
TRACKHOLD
CLOCK
OUTPUT/CONTROL REGISTER
C_EXT
CONVST
AGND AGND DGND CLK SCLK TFS RFS DATA DATA SMODE
IN
OUT IN
*NO SCALING ON AD7890-2
Power dissipation in normal mode is low at 30 mW typ and the
part can be placed in a standby (power-down) mode if it is not
required to perform conversions. The AD7890 is fabricated in
Analog Devices’ Linear Compatible CMOS (LC²MOS) process,
a mixed technology process that combines precision bipolar cir-
cuits with low power CMOS logic. The part is available in a
24-pin, 0.3" wide, plastic or hermetic dual-in-line package or in
a 24-pin small outline package (SOIC).
PRODUCT HIGHLIGHTS
1. Complete 12-Bit Data Acquisition System on a Chip
The AD7890 is a complete monolithic ADC combining an
eight-channel multiplexer, 12-bit ADC, +2.5 V reference and
a track/hold amplifier on a single chip.
2. Separate Access to Multiplexer and ADC
The AD7890 provides access to the output of the multiplexer
allowing one antialiasing filter for eight channels—a consid-
erable saving over the eight antialiasing filters required if the
multiplexer was internally connected to the ADC.
3. High Speed Serial Interface
The part provides a high speed serial interface for easy
connection to serial ports of microcontrollers and DSP
processors.
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.
© Analog Devices, Inc., 1996
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