Part Number:UCC28780
Hi,
I use UCC28780 to design a 5Vout design, and I face the issue at light load.
1. When power on the board with 0A load, the output voltage is not regulated to 5Vout, varies between 6.2V~6.9V. It was chared when the burst on period, and discharged when the burst off period.
The VDD is always higher than VDD(off). The PWML is on with many counts during burst on, and PWMH is disabled.
I power on the board with more than 0.3A, the board works well.
I capture the waveform as below: CH1: Vclamp_cap; CH2:Vcs; CH3: VDD; CH4: Ipri;
2. When power on the board at 0.1A load with 115Vac. It shows the output voltage is regulated to 5Vout, but the PWML is wrong. The PWML pulse count is not 2. Also the PWMH is good to be disabled.
I capture the waveform as below: CH1: Vclamp_cap; CH2:Vcs; CH3: VDD; CH4: Ipri;
If power on the board with 0.3A load or more, the board can work well.
And then, decrease the load to 0A, the board still works well without any abnormal phenomenon.
It only works failed when power on with 0.2A load or less.
Please help provide your suggestion.
BR