Simultaneous Sampling
Dual 250 kSPS 12-Bit ADC
a
AD7862
FEATURES
FUNCTIONAL BLOCK DIAGRAM
Two Fast 12-Bit ADCs
Four Input Channels
V
REF
V
DD
Simultaneous Sampling & Conversion
4 s Throughput Time
Single Supply Operation
Selection of Input Ranges:
؎10 V for AD7862-10
+2.5V
REFERENCE
2kΩ
AD7862
SIGNAL
SCALING
TRACK/
HOLD
V
V
A1
؎2.5 V for AD7862-3
MUX
MUX
12-BIT
ADC
SIGNAL
SCALING
0 V to 2.5 V for AD7862-2
High Speed Parallel Interface
Low Power, 60 mW typ
Power Saving Mode, 50 W typ
Overvoltage Protection on Analog Inputs
14-Bit Pin Compatible Upgrade (AD7863)
B1
DB0
OUTPUT
LATCH
SIGNAL
SCALING
V
V
DB11
A2
TRACK/
HOLD
12-BIT
ADC
SIGNAL
SCALING
B2
CS
RD
CONVERSION
CONTROL LOGIC
CLOCK
APPLICATIONS
AC Motor Control
Uninterrupted Power Supplies
Data Acquisition Systems
Communications
A0
BUSY CONVST
AGND AGND DGND
GENERAL DESCRIPTION
The AD7862 is fabricated in Analog Devices’ Linear Compat-
ible CMOS (LC2MOS) 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.
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 (VA1 & VA2 or VB1 & VB2) 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.
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.
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 VA1 or VB1, while the second read accesses the result
from VA2 or VB2, 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.
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.
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.
5. The part features very tight aperture delay matching between
the two input sample-and-hold amplifiers.
REV. 0
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.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 617/329-4700
Fax: 617/326-8703
World Wide Web Site: http://www.analog.com
© Analog Devices, Inc., 1996
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