AP8803

Document number: DS31970 Rev. 5 - 2

6 of 10

www.diodes.com

August 2012

© Diodes Incorporated

AP8803

LED Current Dimming

The LED current can be dimmed in two ways;

1.

Analog Dimming: Where a DC voltage is applied to the CTRL pin.

or

2.

PWM Dimming: Where a Pulse Width Modulated (PWM) signal is applied to the CTRL pin.

Analog Dimming

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

=

A DC signal from 0.3V to 2.5V applied to the CTRL pin will vary the LED current from 24% to 200% of nominal LED current. This gives an

approximate 8:1 dimming range; care, should be exercised when overdriving the CTRL pin to 200% of nominal LED current not to exceed the

power dissipation of the package.

circuit shown on Figure 1, for different voltages applied on the CTRL pin.

external DC voltage lower than 2.5V and higher than 0.2V).

LED current Versus RSET and VCTRL

0.2

0.3

0.39

0.47

3

0.82

1

1.5

2

3

0.82

0.75

2

1.5

1

0.75

0.47

0.3

0.1

0.15

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