2
LC MOS 8-Channel, 12-Bit
Serial, Data Acquisition System
a
AD7890
FUNCTIO NAL BLO CK D IAGRAM
FEATURES
Fast 12-Bit ADC w ith 5.9 s Conversion Tim e
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
MUX SHA REF OUT/
VDD
OUT IN
REF IN
2kΩ
SIGNAL
SCALING*
+2.5V
REFERENCE
VIN1
VIN2
SIGNAL
SCALING*
AD7890
Allow s Separate Access to Multiplexer and ADC
On-Chip Track/ Hold Am plifier
On-Chip Reference
High Speed, Flexible, Serial Interface
Single Supply, Low Pow er Operation (50 m W m ax)
Pow er-Dow n Mode (75 W typ)
SIGNAL
VIN3
VIN4
VIN5
VIN6
VIN7
VIN8
SCALING*
CEXT
SIGNAL
SCALING*
M
U
X
SIGNAL
SCALING*
CONVST
SIGNAL
SCALING*
12-BIT
ADC
SIGNAL
SCALING*
TRACKHOLD
SIGNAL
SCALING*
OUTPUT/CONTROL REGISTER
CLOCK
GENERAL D ESCRIP TIO N
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).
AGND AGND
DGND CLK
IN
SCLK
DATA SMODE
IN
TFS
DATA
OUT
RFS
*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. T he 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. T he 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).
T he multiplexer on the part is independently accessible. T his
allows the user to insert an antialiasing filter or signal condition-
ing, if required, between the multiplexer and the ADC. T his
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. T he 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.
P RO D UCT H IGH LIGH TS
1. Complete 12-Bit Data Acquisition System on a Chip
T he 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
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.
T he 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
T he part provides a high speed serial interface for easy
connection to serial ports of microcontrollers and DSP
processors.
REV. A
Inform ation furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assum ed by Analog Devices for its
use, nor for any infringem ents of patents or other rights of third parties
which m ay result from its use. No license is granted by im plication or
otherwise under any patent or patent rights of Analog Devices.
© Analog Devices, Inc., 1996
One Technology Way, P.O. Box 9106, Norw ood, MA 02062-9106, U.S.A.
Tel: 617/ 329-4700
Fax: 617/ 326-8703