top249r over temperature issue
I designed the top249r into a product a few years ago. Now we are experiencing field failures where the device heat dissipation increases rapidly [within about 5 minutes from power on] under even very light load conditions resulting in thermal shut-down. This occurs at room temperature. The measured case temperature during normal operation at room temperature at full load in our lab is about 60C. I have some unhappy customers that are experiencing these failures. The failed product[s] simply cycle on and off every 5-10 minutes. Replacing the top249 returns the product to proper operation. For how long? What am I missing here? What should I be looing for in terms of initial failure mechanism?
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robertb@transition.com
952-996-1546
I have supplied my contact information now three times!!
I have looked at waveforms of many power supplies based on the top249r and find no issue. I have tested in thermal chamber at 50C ambient without issue. The case temperture of the top249r in the failed returned product rises under no load at 21C [room temperture] to 115-120C within a few minutes, the device shuts down and then repeats. Replacing the top249r removes the issue. What is the problem with the top249r that can cause the device to enter this mode. Is there something that can cause the internal FET RDSON to increase over time? Is there some event that can cause this tentancy for the top249r to malfunction?
We are finding that so far all of the field failures have the following markings on the top249r device: J205, TOP249R, 19014A. Perhaps there is something to be gained by knowing this device marking information.
Pls. give me your contact info.