a
FEATURES
256-Position
Replaces 1, 2, or 4 Potentiometers
1 k⍀, 10 k⍀, 50 k⍀, 100 k⍀
Power Shutdown—Less than 5 A
3-Wire SPI-Compatible Serial Data Input
10 MHz Update Data Loading Rate
2.7 V to 5.5 V Single-Supply Operation
Midscale Preset
APPLICATIONS
Mechanical Potentiometer Replacement
Programmable Filters, Delays, Time Constants
Volume Control, Panning
Line Impedance Matching
Power Supply Adjustment
1-/2-/4-Channel
Digital Potentiometers
AD8400/AD8402/AD8403
FUNCTIONAL BLOCK DIAGRAM
AD8403
VDD
8-BIT 8
LATCH
DAC
SELECT
DGND
CK RS
1
2
8-BIT
LATCH
3
A1, A0 4
10-BIT
SERIAL
LATCH
SDI
D
SHDN
8
CK RS
2
8
8-BIT
LATCH
RDAC2
SHDN
8
CK RS
CK Q RS
CLK
8-BIT 8
LATCH
CS
RDAC1
RDAC3
SHDN
RDAC4
CK RS
SDO
The AD8400/AD8402/AD8403 provide a single, dual or quad
channel, 256 position digitally controlled variable resistor (VR) device.
These devices perform the same electronic adjustment function as
a potentiometer or variable resistor. The AD8400 contains a single
variable resistor in the compact SO-8 package. The AD8402 contains
two independent variable resistors in space-saving SO-14 surfacemount packages. The AD8403 contains four independent variable
resistors in 24-lead PDIP, SOIC, and TSSOP packages. Each part
contains a fixed resistor with a wiper contact that taps the fixed
resistor value at a point determined by a digital code loaded into the
controlling serial input register. The resistance between the wiper and
either endpoint of the fixed resistor varies linearly with respect to the
digital code transferred into the VR latch. Each variable resistor
offers a completely programmable value of resistance, between the A
terminal and the wiper or the B terminal and the wiper. The fixed
A to B terminal resistance of 1 kΩ, 10 kΩ, 50 kΩ, or 100 kΩ has a ±1%
channel-to-channel matching tolerance with a nominal temperature
coefficient of 500 ppm/°C. A unique switching circuit minimizes the
high glitch inherent in traditional switched resistor designs avoiding
any make-before-break or break-before-make operation.
Each VR has its own VR latch that holds its programmed resistance
value. These VR latches are updated from an SPI compatible serialto-parallel shift register that is loaded from a standard 3-wire
serial-input digital interface. Ten data bits make up the data word
clocked into the serial input register. The data word is decoded where
the first two bits determine the address of the VR latch to be loaded,
the last eight bits are data. A serial data output pin at the opposite end
of the serial register allows simple daisy-chaining in multiple VR
applications without additional external decoding logic.
The reset (RS) pin forces the wiper to the midscale position by
loading 80H into the VR latch. The SHDN pin forces the resistor
REV. C
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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. No license is granted by implication or otherwise
under any patent or patent rights of Analog Devices.
RS
A2
W2
B2
AGND2
A3
W3
B3
AGND3
A4
W4
B4
AGND4
SHDN
to an end-to-end open circuit condition on the A terminal and
shorts the wiper to the B terminal, achieving a microwatt power
shutdown state. When SHDN is returned to logic high, the
previous latch settings put the wiper in the same resistance
setting prior to shutdown. The digital interface is still active in
shutdown so that code changes can be made that will produce
new wiper positions when the device is taken out of shutdown.
The AD8400 is available in both the SO-8 surface-mount and the
8-lead plastic DIP package.
The AD8402 is available in both surface mount (SO-14) and
14-lead plastic DIP packages, while the AD8403 is available in a
narrow body 24-lead plastic DIP and a 24-lead surface-mount
package. The AD8402/AD8403 are also offered in the 1.1 mm thin
TSSOP-14/TSSOP-24 packages for PCMCIA applications. All
parts are guaranteed to operate over the extended industrial temperature range of –40°C to +125°C.
100
RWA(D), RWB(D) – % of Nominal RAB
GENERAL DESCRIPTION
SHDN
A1
W1
B1
AGND1
RWA
RWB
75
50
25
0
0
64
128
CODE – Decimal
192
255
Figure 1. RWA and RWB vs. Code
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700
www.analog.com
Fax: 781/326-8703
© Analog Devices, Inc., 2002
