LC2MOS 8-Channel, 12-Bit
Serial, Data Acquisition System
a
AD7890
FUNCTIONAL BLOCK DIAGRAM
FEATURES
Fast 12-Bit ADC with 5.9 s Conversion Time
Eight Single-Ended Analog Input Channels
Selection of Input Ranges:
MUX SHA REF OUT/
V
DD
OUT IN
REF IN
؎10 V for AD7890-10
0 V to 4.096 V for AD7890-4
0 V to 2.5 V for AD7890-2
SIGNAL
2k⍀
V
2.5V
REFERENCE
IN1
SCALING*
SIGNAL
SCALING*
V
IN2
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)
SIGNAL
V
IN3
SCALING*
C
EXT
SIGNAL
SCALING*
V
IN4
MUX
SIGNAL
SCALING*
V
IN5
CONVST
SIGNAL
SCALING*
V
IN6
12-BIT
ADC
SIGNAL
SCALING*
V
IN7
SIGNAL
SCALING*
TRACK/HOLD
OUTPUT/CONTROL REGISTER
V
IN8
GENERAL DESCRIPTION
AD7890
CLOCK
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
SCLK
TFS
RFS
SMODE
CLK
IN
DATA DATA
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
circuits with low power CMOS logic. The part is available in a
24-lead, 0.3" wide, plastic or hermetic dual-in-line package or in
a 24-lead small outline package (SOIC).
The multiplexer on the part is independently accessible. This
allows the user to insert an antialiasing filter or signal conditioning,
if required, between the multiplexer and the ADC. This means
that one antialiasing filter can be used for all eight channels.
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
bidirectional serial interface port. The part contains an on-chip
control register, allowing control of channel selection, conver-
sion start and power-down via the serial port. Versatile, high
speed logic ensures easy interfacing to serial ports on microcon-
trollers and digital signal processors.
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.
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.
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 con-
nection to serial ports of microcontrollers and DSP processors.
REV. B
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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Tel: 781/329-4700
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© Analog Devices, Inc., 2001