Datasheet

AD5227
Rev. B | Page 12 of 16
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
04419-0-033
UP/DOWN
MR RESET
V
CC
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.
04419-0-034
U3
AD5227
DIGITAL
POTENTIOMETER
CLK
1
V
DD
8
U/D
2
CS
7
A13 B1 6
GND
4
W1
5
B1
A1
W1
U2
LS7084
QUADRATURE
DECODER
RBIAS
1
CLK
8
V
DD
2
U/D
7
VSS
3
X4/X1
6
A
4
B
5
B
C
A
U1
ROTARY
ENCODER
RE11CT-V1Y12-EF2CS
R3
10kΩ
R1
10kΩ
R2
10kΩ
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 V
F
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.
04419-0-035
A
W
B
10kΩ
V
DD
GND
CS
CLK
U/D
U1
AD5227
C1
1μF
C2
0.1μF
5V
U2
AD8591
+
–
V+
V–
SD
5V
C3
0.1μF
R1
6Ω
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.
04419-0-036
A
W
B
10kΩ
R1
418kΩ
GND
U2
AD5227
V
DD
5V
CS
CLK
U/D
5V
U3
AD8591
+
–
V+
V–
5V
PWM
V
IN
V
OUT
GND
U1
ADP3333
ARM-1.5
SD
R
SET
0.1Ω
VL
ID
D1
Figure 34. Adjustable Current Source for LED Driver
The load current can be found as the V
WB
of the AD5227
divided by R
SET
.
SET
WB
D
R
V
I =
(5)