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A couple of questions for your ADD5211 LED driver

Question asked by Kaos on Aug 31, 2015
Latest reply on Sep 4, 2015 by Kaos

Dear Sir/Madam,

 

Our customer is evaluating with your ADD5211 LED driver.

So he just tossed a couple of questions as following

He designed 2 ganged on 2 ch ,and each channels pull 3 LEDs. 

Vf=1.8V LED

 

Q-1

Can your ADD5211 drive as current dimming control not PWM control?

He needs the dimming fuction as current control.

PWM bring thr flicker for LED on-off.

This flicker make bad for his products.

 

Q-2

If he put the over 22uF for Cout on your datasheet page-15, then what trouble coming? Growth ripple noise?

 

Q-3

As for thr PWM frequency,

when 300Hz:dimming=1000:1

So when 25kHz:dimming=?:1, =1000:1 correct?

This is brought from page-1 on your datasheet FEATURES.

 

Q-4

If he put the frequency of PWM from 300Hz to 20kHz, then he just found that the charge pump voltage become growth high.

Why this result have comin?

 

Anode voltage of LED(as VLED)

duty 0:900, VLED=4V

duty 1:900, VLED=38.6V

duty 2:900, VLED=37V

duty 3:900, VLED=28.2V

.

.

.

duty 8:900, VLED=9.6V

 

But when the PWM freq=300Hz, VLED=4V all.

 

 

Thanks Kaos

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