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AD5227 Datasheet(PDF) 12 Page - Analog Devices

Part No. AD5227
Description  64-Position Up/Down Control Digital Potentiometer
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Maker  AD [Analog Devices]
Homepage  http://www.analog.com
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AD5227 Datasheet(HTML) 12 Page - Analog Devices

 
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AD5227
Rev. B | Page 12 of 1
6
APPLICATIONS
MANUAL CONTROL WITH TOGGLE AND
PUSHBUTTON SWITCHES
The AD5227’s simple interface allows it to be used with
mechanical switches for simple manual operation. The states of
the CS and U/D can be selected by toggle switches and the CLK
input can be controlled by a pushbutton switch. Because of the
numerous bounces due to contact closure, the pushbutton
switch should be debounced by flip-flops or by the ADM812 as
shown in
.
Figure 31
UP/DOWN
MR
RESET
VCC
GND
ADM812
CLK
AD5227
CS
U/D
5V
INCREMENT
Figure 31. Manual Push Button Up/Down Control
MANUAL CONTROL WITH ROTARY ENCODER
Figure 32 shows another way of using AD5227 to emulate
mechanical potentiometer in a rotary knob operation. The
rotary encoder U1 has a C ground terminal and two out-of-
phase signals, A and B. When U1 is turned clockwise, a pulse
generated from the B terminal leads a pulse generated from the
A terminal and vice versa. Signals A and B of U1 pass through a
quadrature decoder U2 that translates the phase difference
between A and B of U1 into compatible inputs for U3 AD5227.
Therefore, when B leads A (clockwise), U2 provides the AD5227
with a logic high U/D signal, and vice versa. U2 also filters
noise, jitter, and other transients as well as debouncing the
contact bounces generated by U1.
U3
AD5227
DIGITAL
POTENTIOMETER
CLK
1
VDD
8
U/D
2
CS
7
A1
3
B1 6
GND
4
W1 5
B1
A1
W1
U2
LS7084
QUADRATURE
DECODER
RBIAS
1
CLK
8
VDD
2
U/D
7
VSS
3
X4/X1
6
A
4
B
5
B
C
A
U1
ROTARY
ENCODER
RE11CT-V1Y12-EF2CS
R3
10k
Ω
R1
10k
Ω
R2
10k
Ω
5V
Figure 32. Manual Rotary Control
ADJUSTABLE LED DRIVER
The AD5227 can be used in many electronics-level adjustments
such as LED drivers for LCD panel backlight control. Figure 33
shows an adjustable LED driver. The AD5227 sets the voltage
across the white LED D1 for the brightness control. Since U2
handles up to 250 mA, a typical white LED with VF of 3.5 V
requires a resistor, R1, to limit the U2 current. This circuit is
simple but not power-efficient, therefore the U2 shutdown pin
can be toggled with a PWM signal to conserve power.
A
W
B
10k
Ω
VDD
GND
CS
CLK
U/D
U1
AD5227
C1
1
μF
C2
0.1
μF
5V
U2
AD8591
+
V+
V–
SD
5V
C3
0.1
μF
R1
6
Ω
WHITE
LED
D1
PWM
Figure 33. Low Cost Adjustable LED Driver
ADJUSTABLE CURRENT SOURCE FOR LED DRIVER
Since LED brightness is a function of current rather than
forward voltage, an adjustable current source is preferred over a
voltage source as shown in Figure 34.
A
W
B
10k
Ω
R1
418k
Ω
GND
U2
AD5227
VDD
5V
CS
CLK
U/D
5V
U3
AD8591
+
V+
V–
5V
PWM
VIN
VOUT
GND
U1
ADP3333
ARM-1.5
SD
RSET
0.1
Ω
VL
ID
D1
Figure 34. Adjustable Current Source for LED Driver
The load current can be found as the VWB of the AD5227
divided by RSET.
SET
WB
D
R
V
I
=
(5)


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