Other Parts Discussed in Thread: TL431
Dear TI team:
My customer used UCC28780 for adapter application. But the UCC28780 can't power up:
The attachment is the schematic diagram and PCB, and the debugging situation is: RUN, PWMH, PWML no output for low level; SWS=18V, HVG= 16.7V, VDD= 15.9V, FB= 4.49V, RTZ= 3.48V, RDM= 0.6V, BUR=1V, REF=5V. The EDS of UCC28780 was tested in the period of 0.5~0.8, and the devices were tested without short circuit and open circuit.
The output voltage is 3-5V when the first time power on, and HVG can also return to 11V. After adjust resisitence of TL431, there is no output. The HVG voltage returns to about 16-17V, which is the same states every time after it power on.
What maybe the problem?
The picture is the waveform of VDD power on, the attchment is SCH.
