Diodes AL8806Q - Manual (Page 9)

AL8806Q
Document number: DS36905 Rev. 1 - 2
9 of 13
www.diodes.com
April 2014
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AL8806Q
Application Information
(cont.)
Soft Start
The AL8806Q does not have in-built soft-start action – this provides very fast turn off of the output the stage improving PWM dimming accuracy;
nonetheless, adding an external capacitor from the CTRL pin to ground will provide a soft-start delay. This is achieved by increasing the time taken
for the CTRL voltage 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.
Adding a capacitor increases the time taken for the output to reach 90% of its final value, this delay is 0.1ms/nF, but will impact on the PWM
dimming accuracy depending on the delay introduced.
Figure 4 Soft Start with 22nF Capacitor on CTRL pin (V
IN
= 30V, I
LED
= 667mA, 1 LED)