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?