al8805 Diodes, Inc., al8805 Datasheet - Page 11

• Manufacturer Part Number: al8805
• Description: High Efficiency 30v 1a Buck Led Driver
• Manufacturer: Diodes, Inc.

Applications Information
PWM Dimming (cont.)
The PWM pin is designed to be driven by both 3.3V and
5V logic levels directly from a logic output with either an
open drain output or push-pull output stage.
\
AL8805
Document number: DS35030 Rev. 1 - 2
Figure 32. Soft start with 22nF capacitor on CTRL pin (V
(cont.)
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HIGH EFFICIENCY 30V 1A BUCK LED DRIVER
Soft Start
The AL8805 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.
IN
= 30V, I
LED
= 667mA, 1 LED)
AL8805
© Diodes Incorporated
September 2010