I have some prototype boards where 1 of the 4 had an inductor squeal during the first 5 seconds of operation but then is fine. The backlight circuit can be turned on and off using the two inputs provided without causing the inductor to squeal again. If the unit is left off for around 5 minutes, then turned back on, the inductor squeals again for around 5 seconds. I have had switchers do this before and it was usually a poor quality capacitor or the inductor itself.
My question: What is the best way to troubleshoot the inductor squeal to determine what is actually causing the problem. My concern in this circuit is I run the backlight at 27.3V which is close to the over voltage threshold but only use 20 mA total current (10mA from each strand). I am getting close to production and would rather not have the first 1000 off the line squeal.
Thanks for any ideas / directions
