Hello,
I am using the UCC28C45D for a basic flyback design. We have a differential amplifier feeding back the divided down output votlage. Out of 12 units we are seeing two of them that exhibit a FB pin voltage that is out of datasheet spec. One is at 2.385 V and the other is at 2.435 V. The datasheet total variation minimum is no less than 2.45 V. This is causing our output voltage to be out of spec. Also, the VREF pin voltage seems to correlate with this low voltage. One of the failing units has a VREF that is out of spec (4.770 V, 4.869 V), which should be not less than 4.82 V according to the datasheet.
After some investigation we found that there was no decoupling capacitor installed on the VREF pin. We do not see any issues as far as start-up stresses or shutdown stresses. The VREF seems to be regulating without any oscillations. Even after we installed the decoupling capacitor the voltage stayed the same on the failing unit. Is there a possibility that not having a VREF decoupling capacitor could cause these parts to get damaged and have a failing reference voltage?
Any other thoughts that may be the issue?
Thanks,
Sam Fritzinger