LC
2
MOS 8-Channel, 12-Bit
Serial Data Acquisition System
AD7890
Rev. C
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FEATURES
Fast 12-bit ADC with 5.9 μs 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 maximum)
Power-down mode (75 μW typ)
GENERAL DESCRIPTION
The AD7890 is an 8-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
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,
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
specified for dynamic performance parameters including
harmonic distortion and signal-to-noise ratio.
FUNCTIONAL BLOCK DIAGRAM
TRACK/HOLD
2kΩ
AD7890
C
EXT
CONVST
MUX
OUT
SH
IN
REF OUT/
REF IN
AGND AGND DGND SCLK TFS RFS DATA
OUT
DATA
IN
SMODE
V
IN1
DD
V
IN2
V
IN3
V
IN4
V
IN5
V
IN6
V
IN7
V
IN8
1
NO SCALING ON AD7890-2
CLOCK
OUTPUT/CONTROL REGISTER
12-BIT
ADC
MUX
2.5V
REFERENCE
SIGNAL
SCALING
1
SIGNAL
SCALING
1
SIGNAL
SCALING
1
SIGNAL
SCALING
1
SIGNAL
SCALING
1
SIGNAL
SCALING
1
SIGNAL
SCALING
1
SIGNAL
SCALING
1
CLK
IN
01357-001
Figure 1.
Power dissipation in normal mode is low at 30 mW typical 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, Inc.’s Linear Compatible CMOS (LC
2
MOS)
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 ceramic dual-in-line package or in
a 24-lead small outline package (SOIC_W).
PRODUCT HIGHLIGHTS
1. Complete 12-Bit Data Acquisition System-on-a-Chip.
The AD7890 is a complete monolithic ADC combining an
8-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 8 channels—
a considerable savings over the 8 antialiasing filters required if
the multiplexer is 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.
