AD7890_15 Datasheet, PDF (1/28 Pages) Analog Devices – LC MOS 8-Channel, 12-Bit Serial Data Acquisition System

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.
LC²MOS 8-Channel, 12-Bit
Serial Data Acquisition System
AD7890
FUNCTIONAL BLOCK DIAGRAM
V_DD
MUX SHA REF OUT/
OUT IN REF IN
V_IN1
V_IN2
V_IN3
V_IN4
V_IN5
V_IN6
V_IN7
V_IN8
SIGNAL
SCALING¹
SIGNAL
SCALING¹
SIGNAL
SCALING¹
SIGNAL
SCALING¹
SIGNAL
SCALING¹
SIGNAL
SCALING¹
SIGNAL
SCALING¹
SIGNAL
SCALING¹
AD7890
2kΩ
2.5V
REFERENCE
MUX
12-BIT
ADC
TRACK/HOLD
CLOCK
OUTPUT/CONTROL REGISTER
C_EXT
CONVST
AGND AGND DGND CLK
IN
SCLK TFS RFS DATA DATA SMODE
OUT IN
1_{NO SCALING ON AD7890-2}
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 (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 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.
Rev. C
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