LNK304GN-TL shuts down at less than 50 degrees C

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We have had 100% of these chips fail during testing with as low as 40 degrees C ambient temperature. The voltage at the drain is 392 VDC and the current draw is less than 75ma maximum.

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Hi Chuckleng,
Did it failed during start-up condition full load or no load? Is your input voltage DC source of 392V? What pins of the IC got damaged? In case you captured some waveforms, can you also share it to us?
Regards,
Jedidiah

Hi Jedidiah,
It failed after running for a while when the temperature of the chip case reached 104 degrees C. Not sure why it is getting so hot we are only using about 70ma of current and the ambient temperature in the unit is 54 degrees C. The IC was not damaged it just shut down and didn't come back up until it cooled off to about 50 degrees C. We do not have any waveforms.

Hi Chuckleng,
It's the Over temperature protection of the IC that triggers the shutdown. We have hysteresis wherein after cool down of the IC, it will start operating again. Can you share to me the actual board that you used? The parts and the layout? Let check how we can improve the temperature performance of the circuit.
Regards,
Jedidiah