I`m using the ADD5211 to drive a LCD backlight, but sometimes (very rare) it doesn´t power on.
After connecting the EN-pin or the UVLO-pin shortly to ground it starts again.
Unfortunately I didn´t connect the Fault-pin, so I can`t monitor any fault state.
I tried to connect EN-pin or UVLO-pin via a 100kOhm resistor to VIN, but without any success.
I can also reproduce it by permanent powering the ADD5211 and switching off/on the EN-pin.
I already ordered the evaluation board and use quite the same values for all components,
but could not reproduce the faulty behavior.
Production date ADD5211: 1319 @ADD5211-Evalboard and 1634 in my design
The only latched fault conditions causing the ADD5211 to turn off are LED short or LED open, these can also be indirectly triggered by another condition such as in-rush current. Since you could replicate the issues by repeatedly enabling and disabling the part I would exclude connection issues with the backlight.
Could you please let me know the following:
- Is LSD pin biased as suggested in the datasheet or tied to VDD? If biased, could you try to force it to VDD and see if the problem goes away? I am not suggesting this as a solution but to isolate the origin of the issue.
- How many LEDs, color and strings are used in your application?
- Could you confirm the values for the passive components used and the input supply voltage?
-> I would need the exact p/n for COUT, L1, D1, Q1, Rcs and Css
- If needed, would you be able to probe the FAULT pin together with VOUT with a two channels oscilloscope?
thank you for your quick answer and your guidelines.
First I figured out that the FAULT pin stays high under fault condition.
After I found the main different between my circuit and the eval board.
*** 100nF for emc reasons between U_out and FB ***
Without the capacitor the ADD5211 works well!
Thank you again and best regards,Sven