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AD5222 Datasheet(PDF) 8 Page - Analog Devices

Part No. AD5222
Description  Increment/Decrement Dual Digital Potentiometer
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Maker  AD [Analog Devices]
Homepage  http://www.analog.com
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AD5222
–8–
REV. 0
OPERATION
The AD5222 provides a 128-position, digitally-controlled, variable
resistor (VR) device. Changing the VR settings is accomplished
by pulsing the CLK pin while
CS is active low. The U/D (UP/
DOWN) control input pin controls the direction of the increment.
When the wiper hits the end of the resistor (Terminal A or B)
additional CLK pulses no longer change the wiper setting. The
wiper position is immediately decoded by the wiper decode logic
changing the wiper resistance. Appropriate debounce circuitry is
required when push-button switches are used to control the
count sequence and direction of count. The exact timing require-
ments are shown in Figure 2. The AD5222 powers ON in a
centered wiper position, exhibiting nearly equal resistances of
RWA and RWB.
DECODE
UP/DOWN
COUNTER
AD5222
VSS
A1
W1
B1
DECODE
UP/DOWN
COUNTER
A2
W2
B2
POR
DAC
SELECT
AND
ENABLE
CLK
CS
U/
D
DACSEL
MODE
GND
VDD
Figure 29. Block Diagram
DIGITAL INTERFACING OPERATION
The AD5222 contains a push-button controllable interface. The
active inputs are clock (CLK),
CS and up/down (U/D). While
the MODE, and DACSEL pins control common updates or
individual updates. The negative-edge sensitive CLK input
requires clean transitions to avoid clocking multiple pulses into
the internal UP/DOWN counter register, Figure 30. Standard
logic families work well. If mechanical switches are used for
product evaluation a flip-flop or other suitable means should
debounce them. When
CS is taken active low, the clock begins
to increment or decrement the internal up/down counter, depen-
dent upon the state of the U/
D control pin. The UP/DOWN
counter value (D) starts at 40H at system power ON. Each new
CLK pulse will increment the value of the internal counter by
1 LSB until the full-scale value of 7FH is reached, as long as the
U/
D pin is logic high. If the U/D pin is taken to logic low, the
counter will count down, stopping at code 00H (zero-scale).
Additional clock pulses on the CLK pin are ignored when the
wiper is at either the 00H position or the 7FH position. The
detailed digital logic interface circuitry is shown in Figure 30.
RDAC 1
U/
D
COUNTER
RDAC 2
U/
D
COUNTER
CLK
CS
U/
D
DACSEL
MODE
Figure 30. Detailed Digital Logic Interface Circuit
All digital inputs (
CS, U/D, CLK, MODE, DACSEL) are
protected with a series input resistor and parallel Zener ESD
structure shown in Figure 31. All potentiometer terminal pins
(A, B, W) are protected from ESD as shown in Figure 32.
LOGIC
1k
VSS
Figure 31. Equivalent ESD Protection Digital Pins
20
A, B, W
VSS
Figure 32. Equivalent ESD Protection Analog Pins
D0
D1
D2
D3
D4
D5
D6
RDAC
UP/DOWN
CNTR
&
DECODE
W
B
RS = RNOMINAL/128
RS
RS
RS
A
RS
Figure 33. AD5222 Equivalent RDAC Circuit




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