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use, nor for any infringements of patents or other rights of third parties
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otherwise under any patent or patent rights of Analog Devices.
a
AD7862
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 617/329-4700 World Wide Web Site: http://www.analog.com
Fax: 617/326-8703 © Analog Devices, Inc., 1996
Simultaneous Sampling
Dual 250 kSPS 12-Bit ADC
FUNCTIONAL BLOCK DIAGRAM
CLOCK
DGND
DB0
BUSY
RD
CS
CONVST
AD7862
CONVERSION
CONTROL LOGIC
V
A1
AGND
V
REF
+2.5V
REFERENCE
2kΩ
AGND
TRACK/
HOLD
V
DD
DB11
OUTPUT
LATCH
MUX
A0
12-BIT
ADC
12-BIT
ADC
TRACK/
HOLD
MUX
SIGNAL
SCALING
SIGNAL
SCALING
SIGNAL
SCALING
SIGNAL
SCALING
V
B1
V
A2
V
B2
FEATURES
Two Fast 12-Bit ADCs
Four Input Channels
Simultaneous Sampling & Conversion
4 ms Throughput Time
Single Supply Operation
Selection of Input Ranges:
610 V for AD7862-10
62.5 V for AD7862-3
0 V to 2.5 V for AD7862-2
High Speed Parallel Interface
Low Power, 60 mW typ
Power Saving Mode, 50 mW typ
Overvoltage Protection on Analog Inputs
14-Bit Pin Compatible Upgrade (AD7863)
APPLICATIONS
AC Motor Control
Uninterrupted Power Supplies
Data Acquisition Systems
Communications
GENERAL DESCRIPTION
The AD7862 is a high speed, low power, dual 12-bit A/D
converter that operates from a single +5 V supply. The part
contains two 4 µs successive approximation ADCs, two track/
hold amplifiers, an internal +2.5 V reference and a high speed
parallel interface. There are four analog inputs that are grouped
into two channels (A & B) selected by the A0 input. Each
channel has two inputs (V
A1
& V
A2
or V
B1
& V
B2
) that can be
sampled and converted simultaneously thus preserving the
relative phase information of the signals on both analog inputs.
The part accepts an analog input range of ±10 V (AD7862-10),
±2.5 V (AD7862-3) and 0–2.5 V (AD7862-2). Overvoltage
protection on the analog inputs for the part allows the input
voltage to go to ±17 V, ±7 V or +7 V, respectively, without
causing damage.
A single conversion start signal (
CONVST) places both track/
holds into hold simultaneously and initiates conversion on both
inputs. The BUSY signal indicates the end of conversion, and
at this time the conversion results for both channels are avail-
able to be read. The first read after a conversion accesses the
result from V
A1
or V
B1
, while the second read accesses the result
from V
A2
or V
B2
, depending on whether the multiplexer select
A0 is low or high, respectively. Data is read from the part via a
12-bit parallel data bus with standard
CS and RD signals.
In addition to the traditional dc accuracy specifications such as
linearity, full-scale and offset errors, the part is also specified for
dynamic performance parameters including harmonic distortion
and signal-to-noise ratio.
The AD7862 is fabricated in Analog Devices’ Linear Compat-
ible CMOS (LC
2
MOS) process, a mixed technology process
that combines precision bipolar circuits with low power CMOS
logic. It is available in 28-lead SSOP, SOIC and DIP.
PRODUCT HIGHLIGHTS
1. The AD7862 features two complete ADC functions allowing
simultaneous sampling and conversion of two channels. Each
ADC has a 2-channel input mux. The conversion result for
both channels is available 3.6 µs after initiating conversion.
2. The AD7862 operates from a single +5 V supply and
consumes 60 mW typ. The automatic power-down mode,
where the part goes into power down once conversion is
complete and “wakes up” before the next conversion cycle,
makes the AD7862 ideal for battery-powered or portable
applications.
3. The part offers a high speed parallel interface for easy con-
nection to microprocessors, microcontrollers and digital
signal processors.
4. The part is offered in three versions with different analog
input ranges. The AD7862-10 offers the standard industrial
input range of ±10 V; the AD7862-3 offers the common
signal processing input range of ±2.5 V; while the AD7862-2
can be used in unipolar 0 V – +2.5 V applications.
5. The part features very tight aperture delay matching between
the two input sample-and-hold amplifiers.
