Diodes AL8806Q Manuel d'utilisateur télécharger pdf (Page 9)

AL8806Q

Document number: DS36905 Rev. 1 - 2

9 of 13

www.diodes.com

April 2014

L8806Q

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

= 30V, I

LED

= 667mA, 1 LED)

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Diodes AL8806Q Manuel d'utilisateur Page 9