AP8802

1A LED Step-Down Converter

AP8802 Rev. 1

5 of 13

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

0.2

0.33

0.39

0.47

0.56

0.39

0.47

0.56

0.68

0.82

1

3

0.2

0.33

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

200

400

600

800

1000

1200

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