REV. 0
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a
AD5220
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700 World Wide Web Site: http://www.analog.com
Fax: 781/326-8703 © Analog Devices, Inc., 1998
Increment/Decrement
Digital Potentiometer
FUNCTIONAL BLOCK DIAGRAM
UP/
DOWN
CNTR
RS
D
E
C
O
D
E
7
40
H
POR
EN
AD5220
V
DD
A
W
B
GND
CLK
CS
U/D
FEATURES
128 Position
Potentiometer Replacement
10 k⍀, 50 k⍀, 100 k⍀
Very Low Power: 40 A Max
Increment/Decrement Count Control
APPLICATIONS
Mechanical Potentiometer Replacement
Remote Incremental Adjustment Applications
Instrumentation: Gain, Offset Adjustment
Programmable Voltage-to-Current Conversion
Programmable Filters, Delays, Time Constants
Line Impedance Matching
Power Supply Adjustment
GENERAL DESCRIPTION
The AD5220 provides a single channel, 128-position digitally
controlled variable resistor (VR) device. This device performs
the same electronic adjustment function as a potentiometer or
variable resistor. These products were optimized for instrument
and test equipment push-button applications. A choice between
bandwidth or power dissipation are available as a result of the
wide selection of end-to-end terminal resistance values.
The AD5220 contains a fixed resistor with a wiper contact that
taps the fixed resistor value at a point determined by a digitally
controlled UP/DOWN counter. The resistance between the
wiper and either end point of the fixed resistor provides a con-
stant resistance step size that is equal to the end-to-end resis-
tance divided by the number of positions (e.g., R
STEP
= 10 kΩ/
128 = 78 Ω). The variable resistor offers a true adjustable 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
10 kΩ, 50 kΩ, or 100 kΩ has a nominal temperature coefficient
of 800 ppm/°C.
The chip select CS, count CLK and U/D direction control
inputs set the variable resistor position. These inputs that con-
trol the internal UP/DOWN counter can be easily generated
with mechanical or push button switches (or other contact closure
devices). External debounce circuitry is required for the nega-
tive-edge sensitive CLK pin. This simple digital interface elimi-
nates the need for microcontrollers in front panel interface designs.
The AD5220 is available in both surface mount (SO-8) and the
8-lead plastic DIP package. For ultracompact solutions selected
models are available in the thin µSOIC package. All parts are
guaranteed to operate over the extended industrial temperature
range of –40°C to +85°C. For 3-wire, SPI compatible inter-
face applications, see the AD7376/AD8400/AD8402/AD8403
products.
UPCOUNT DETAIL
V
DD
= 5.5V
V
A
= 5.5V
V
B
= 0V
f = 100kHz
CLK
V
WB
50mV/DIV
5V/DIV
Figure 2a. Stair-Step Increment Output
V
DD
= 5.5V
V
A
= 5.5V
V
B
= 0V
f = 60kHz
COUNT
00
H
v 3F
H
v 00
H
V
WR
f
CLK
= 60kHz
Figure 2b. Full-Scale Up/Down Count
AD5220
CS
U/D
CLK
+5V
UP/DOWN
INCREMENT
Figure 1. Typical Push-Button Control Application
