AP8803

Document number: DS31970 Rev. 5 - 2

7 of 10

www.diodes.com

August 2012

© Diodes Incorporated

AP8803

PWM Dimming

A Pulse Width Modulated (PWM) signal with a max resolution of 8-bit, can be applied to the CTRL pin to change the output current to a value

Figure 5 shows the typical PWM response of the AP8800A. An internal filter produces a rump

Figure 5 Typical PWM Dimming Waveform

The recommended method of driving the CTRL pin and controlling the amplitude of the PWM waveform is to use a small NPN switching

transistor as shown below:

Figure 6 Open Collector PWM Dimming Circuit

This scheme uses the internal 200k

Ω resistor between the CTRL pin and the internal voltage reference as a pull-up resistor for the external

transistor eg MMBT3904.

Soft-Start

An external capacitor from the CTRL pin to ground will provide soft-start delay, by increasing the time taken for the voltage on this pin to rise to

the turn-on threshold and by slowing down the rate of rise of the control voltage at the input of the comparator.

The soft-start time is 0.5ms/nF.