UCC3808-1

The datasheet said, you can pull down COMP to GND to force duty cycle to zero. We found it may damage the COMP (affect the reliabilty in normal operation) after do that in many times. I mean if we pull down COMP many times (by a NPN transistor), the COMP will not wotk properly (feedback loop will be instable). After change the IC, it works well again. Is there any reasonale explanation on that?

Dear Junming,

Most likely the problem is that the part is getting too hot. check how much power is being dissipated in the IC. (measure the Vcc current and voltage to get the power being dissipated in the IC) and see what the thermal analysis says the IC junction temperature will be.

The method of controlling the loop is not preferred but many customers do use it successfully. The below information as defined in www.designworldonline.com/.../Feedback-Loops-Using-Integrated-Circuit-Error-Amplifiers.aspx  might be considered.

Regards,