The UCC28740 is the below situation. The schematic is the same as the TI reference design.
There are currently about 500/15000 fail rate
When 90VAC, use end customer-customized FCT equipment for test verification. UCC28740 is not functioning correctly. But when the voltage was raised to 95VAC, the IC that was not working correctly could work normally again. In the past, there was no problem with sending 90VAC during the test. This time, there were a lot of ICs that could not function normally under this condition, so I would like to ask TI for assistance.
1. There are three kinds of data codes in the photo, do these three data codes have problems in the FCT test => yes
2. Please verify whether it is normal on the bench => If the IC of PASS and the IC of NG are exchanged for verification, the original PASS board will become NG, and the original NG board will become PASS
3. Is the data code of the IC that has been tested without problems the same? = According to the text of the IC body, I can't tell which data code the code is produced by the IC, I can only verify it by exchanging PASS with NG IC
4. Has the transformer been exchanged with the tested OK machine before? => Tried to replace the PASS transformer, but it is still NG.