we use ucc256610 for our design we have a problem that need your help
During light load, the transformer emits a buzzing sound that we can not accept When we measured the midpoint voltage(SW) waveform(ch3 pink wave),we observed the pattern shown in Figure 1: the waveform is discontinuous,with a low-frequency component of 170 kHz (when zoomed in) superimposed on a high-frequency waveform of 570 kHz. After applying a load of 0.2 A, the waveform becomes continuous, and the sound returns to normal. we try to change the ratio of LL PIN,it can enter burst mode,but can still see the low frequency in the waveform is it normal for the chip or the parameter we set cause the issue,
we use ER4045 Integrated Transformer for our use the chip is UCC256610 ,input 220vac output +-42V
Tset up Resistor is up560k down150k LLset Resistor up 180k down56k Isense 100pF 82ohm
Lm=68u Lk=18.5uh Ratio is 15:4:4
