Datasheet
AD5228
Rev. A | Page 16 of 20
AUTOMATIC LCD PANEL BACKLIGHT CONTROL
With the addition of a photocell sensor, an automatic brightness
control can be achieved. As shown in Figure 44, the resistance
of the photocell changes linearly but inversely with the light
output. The brighter the light output, the lower the photocell
resistance and vice versa. The AD5228 sets the voltage level that
is gained up by U2 to drive N1 to a desirable brightness. With
the photocell acting as the variable feedback resistor, the change
in the light output changes the R2 resistance, therefore causing
U2 to drive N1 accordingly to regulate the output. This simple
low cost implementation of an LED controller can compensate
for the temperature and aging effects typically found in high
power LEDs. Similarly, for power efficiency, a PWM signal can
be applied at the gate of N2 to switch the LED on and off
without noticeable effect.
04422-0-045
PUSH-UP
BUTTON
PUSH-DOWN
BUTTON
A
W
B
10kΩ
V
DD
GNDPRE
PU
PD
U1
AD5228
C1
1μF
C2
0.1μF
5V
U2
AD8531
+
–
V+
V–
5V
C3
0.1μF
R1
1kΩ
R3
4.75kΩ
R2
5V
PWM
N2
2N7002
N1
2N7002
WHITE
LED
D1
5V
PHOTOCELL
Figure 44. Automatic LCD Panel Backlight Control
AUDIO AMPLIFIER WITH VOLUME CONTROL
The AD5228 and SSM2211 can form a 1.5 W audio amplifier
with volume control that has adequate power and quality for
portable devices such as PDAs and cell phones. The SSM2211
can drive a single speaker differentially between Pins 5 and 8
without any output capacitor. The high-pass cutoff frequency is
f
H1
= 1/(2 × π × R1 × C1). The SSM2211 can also drive two
speakers as shown in Figure 45. However, the speakers must be
configured in single-ended mode, and output coupling capacitors
are needed to block the dc current. The output capacitor and
the speaker load form an additional high-pass cutoff frequency
as f
H2
= 1/(2 × π × R5 × C3). As a result, C3 and C4 must be
large to make the frequency as low as f
H1
.
04422-0-046
PUSH-UP
BUTTON
PUSH-DOWN
BUTTON
A
W
B
10kΩ
V
DD
PRE
GND
PU
PD
U1
AUDIO_INPUT
U3
AD8591
+
–
R4
10kΩ
R3
10kΩ
5V
C6
10μF
C7
0.1μF
5V
±
2.5V p-p
C1
1μF
R1
10kΩ
C2
0.1μF
U2
SSM2211
+
–
V+
6
4
3
2
7
1
8
5
V–
5V
C5
0.1μF
R6
8Ω
R5
8Ω
C3
470μF
C44
470μF
R2
10kΩ
Figure 45. Audio Amplifier with Volume Control