4-Channel, Simultaneous Sampling,
High Speed, 12-Bit ADC
AD7864
FEATURES
FUNCTIONAL BLOCK DIAGRAM
DV
V
DRIVE
AV
V
V
GND
REF
DD
DD
REF
High speed (1.65 μs) 12-bit ADC
4 simultaneously sampled inputs
4 track-and-hold amplifiers
0.35 μs track-and-hold acquisition time
1.65 μs conversion time per channel
HW/SW select of channel sequence for conversion
Single-supply operation
TRACK-AND-HOLD
×4
6kΩ
2.5V
REFERENCE
STBY
DGND
AGND
RD
V
SIGNAL
SCALING
IN1A
V
IN1B
AD7864
V
V
IN2A
IN2B
SIGNAL
SCALING
MUX
V
V
IN3A
IN3B
SIGNAL
SCALING
DB11
DB0
OUTPUT
DATA
REGISTERS
12-BIT
ADC
Selection of input ranges
V
V
IN4A
IN4B
SIGNAL
SCALING
10 V, 5 V for AD7864-1
SOFTWARE
LATCH
DB0 TO DB3
CS
2.5 V for AD7864-3 0 V to 2.5 V, 0 V to 5 V for AD7864-2
High speed parallel interface that allows
Interfacing to 3 V processors
FRSTDATA
WR
BUSY
EOC
CONVERSION
CONTROL LOGIC
INT/EXT CLOCK
SELECT
INT
CLOCK
Low power, 90 mW typical
Power saving mode, 20 μW typical
Overvoltage protection on analog inputs
SL1 SL2 SL3 SL4
CLKIN
AGND AGND
CONVST
H/S
SEL
INT/EXT
CLK
Figure 1.
APPLICATIONS
AC motor control
Uninterrupted power supplies
Data acquisition systems
Communications
Data is read from the part by a 12-bit parallel data bus using the
CS RD
standard and
signals. Maximum throughput for a single
channel is 500 kSPS. For all four channels, the maximum throughput
is 130 kSPS for the read-during-conversion sequence operation.
The throughput rate for the read-after-conversion sequence
operation depends on the read cycle time of the processor. See
the Timing and Control section. The AD7864 is available in a
small (0.3 square inch area) 44-lead MQFP.
GENERAL DESCRIPTION
The AD7864 is a high speed, low power, 4-channel, simulta-
neous sampling 12-bit analog-to-digital converter (ADC) that
operates from a single 5 V supply. The part contains a 1.65 μs
successive approximation ADC, four track-and-hold amplifiers,
a 2.5 V reference, an on-chip clock oscillator, signal conditioning
circuitry, and a high speed parallel interface. The input signals
on four channels sample simultaneously preserving the relative
phase information of the signals on the four analog inputs. The
part accepts analog input ranges of 10 V, 5 V (AD7864-1), 0 V
to +2.5 V, 0 V to +5 V (AD7864-2), and 2.5 V (AD7864-3).
PRODUCT HIGHLIGHTS
1. Four track-and-hold amplifiers and a fast (1.65 μs) ADC for
simultaneous sampling and conversion of any subset of the
four channels.
2. A single 5 V supply consuming only 90 mW typical, makes
it ideal for low power and portable applications. See the
Standby Mode Operation section.
3. High speed parallel interface for easy connection to micro-
processors, microcontrollers, and digital signal processors.
4. Available in three versions with different analog input
ranges. The AD7864-1 offers the standard industrial input
ranges of 10 V and 5 V; the AD7864-3 offers the common
signal processing input range of 2.5 V; the AD7864-2 can
be used in unipolar, 0 V to 2.5 V and 0 V to 5 V,
applications.
Any subset of the four channels can be converted to maximize
the throughput rate on the selected sequence. Select the channels to
convert via hardware (channel select input pins) or software (pro-
gramming the channel select register).
CONVST
A single conversion start signal (
) simultaneously places
all the track-and-holds into hold and initiates a conversion se-
EOC
quence for the selected channels. The
signal indicates the end
5. Features very tight aperture delay matching between the
of each individual conversion in the selected conversion sequence.
The BUSY signal indicates the end of the conversion sequence.
four input sample-and-hold amplifiers.
Rev. D
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 that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarks and registeredtrademarks are theproperty of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
www.analog.com
Fax: 781.461.3113 ©1998–2009 Analog Devices, Inc. All rights reserved.
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