AP8801

500mA LED Step-Down Converter

AP8801 Rev. 1

5 of 11

MARCH 2009

www.diodes.com

LED Current Control

The LED current is controlled by the resistor RSET in Figure 2.

SET

THD

LED

R

V

I

=

If the CTRL pin is driven by an external voltage (lower than 2.5V), the average LED current is:

SET

THD

REF

CTRL

LED

R

V

V

V

I

=

LED current Versus RSET and VCTRL

0.4

0.47

0.56

0.82

1

3

0.47

0.68

0.82

1

1.2

1.5

2

3

1.2

1.5

2

3

1

0.82

0.68

2

1.5

1.2

0

100

200

300

400

500

600

0

0.15

0.3

0.45

0.6

0.75

0.9

1.05

1.2

1.35 1.5

1.65 1.8

1.95 2.1

2.25 2.4

2.55 2.7

2.85

3

RSET value [Ohms]

LED current @

VCTRL = 1.25V

LED current @

VCTRL = 2.5V

LED current @

VCTRL = 0.625V

Application Information