AD5228

Rev. A | Page 15 of 20

APPLICATIONS

MANUAL ADJUSTABLE LED DRIVER

The AD5228 can be used in many electronics-level adjustments

such as LED drivers for LCD panel backlight controls. Figure 41

shows a manually adjustable LED driver. The AD5228 sets the

voltage across the white LED D1 for the brightness control.

3.5 V requires a resistor, R1, to limit U2 current. This circuit is

simple but not power efficient. The U2 shutdown pin can be

toggled with a PWM signal to conserve power.

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

AD8591

+

–

V+

V–

SD

5V

C3

0.1

μF

R1

6

Ω

WHITE

LED

D1

PWM

Figure 41. Low Cost Adjustable LED Driver

ADJUSTABLE CURRENT SOURCE FOR LED DRIVER

Because LED brightness is a function of current rather than of

forward voltage, an adjustable current source is preferred as

SET

WB

D1

R

V

I

=

(7)

The U1 ADP3333ARM-1.5 is a 1.5 V LDO that is lifted above

minimum, there is no current through D1, so the GND pin of U1

is at –1.5 V if U3 is biased with the dual supplies. As a result,

some of the U2 low resistance steps have no effect on the output

supply voltage must be biased with adequate headroom. Similarly,

PWM signal can be applied at the U1 shutdown pin for power

efficiency.

PUSH-UP

BUTTON

PUSH-DOWN

BUTTON

A

W

B

10k

Ω

R1

418k

Ω

GND

PRE

PU

PD

U2

AD5228

5V

5V

U3

AD8591

+

–

V+

V–

5V

PWM

GND

U1

ADP3333

ARM-1.5

SD

0.1

Ω

VL

ID

D1

Figure 42. Adjustable Current Source for LED Driver

ADJUSTABLE HIGH POWER LED DRIVER

The previous circuit works well for a single LED. Figure 43

shows a circuit that can drive three to four high power LEDs.

The ADP1610 is an adjustable boost regulator that provides the

voltage headroom and current for the LEDs. The AD5228 and

the op amp form an average gain of 12 feedback network that

regulated around 0.1 V and adjusted by the digital

potentiometer.

SET

R

LED

R

V

I

SET

=

(8)

to limit maximum LED current. R3 should also be used in par-

allel with AD5228 to limit the LED current within an achievable

range. A wider current adjustment range is possible by lowering

the R2 to R1 ratio as well as changing R3 accordingly.

SS

RT GND

IN

U2

ADP1610

SW

FB

PWM

1.2V

SD

COMP

10nF

390pF

100k

Ω

L1

10

μF

D1

C3

10

μF

R4

13.5k

Ω

D2

D3

D4

C2

10

μF

5V

+

–

AD8541

U1

L1–SLF6025-100M1R0

D1–MBR0520LT1

U3

V+

V–

5V

C8

0.1

μF

U1

AD5228

BA

10k

Ω

R3

200

Ω

W

R1

100

Ω

R2

1.1k

Ω

0.25

Ω

Figure 43. Adjustable Current Source for LEDs in Series