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.

PUSH-UP

BUTTON

PUSH-DOWN

BUTTON

A

W

B

10k

Ω

GND

PRE

PU

PD

U1

AD5228

C1

1

μF

C2

0.1

μF

5V

U2

AD8531

+

–

V+

V–

5V

C3

0.1

μF

R1

1k

Ω

R3

4.75k

Ω

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

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

PUSH-UP

BUTTON

PUSH-DOWN

BUTTON

A

W

B

10k

Ω

PRE

GND

PU

PD

U1

AUDIO_INPUT

U3

AD8591

+

–

R4

10k

Ω

R3

10k

Ω

5V

C6

10

μF

C7

0.1

μF

5V

±2.5V p-p

C1

1

μF R1

10k

Ω

C2

0.1

μF

U2

SSM2211

+

–

V+

6

4

3

2

7

1

8

5

V–

5V

C5

0.1

μF

R6

8

Ω

R5

8

Ω

C3

470

μF

C44

470

μF

R2

10k

Ω

Figure 45. Audio Amplifier with Volume Control