I've just built a prototype power supply with UCC28630. Everything seems to be OK (output voltages, load regulation, line regulation etc), but I can hear a noise (rather low frequency "whirr", not a typical "hiss") from transformer, regardless of PS load (loaded PS is louder, but noise is exactly the same). I've changed RCS resistor to move "operating point" to higher frequencies (about 60kHz) and to light load mode (30kHz) - no change. Frequency dithering works fine (+/- 7%), but there is some additional jitter of mosfet on-time - about 500ns. Filter capacitors of CS and VSENSE are placed very near to IC pins, layout optimized for PS (no ground loops etc). Adding more filter caps to VCC - no change. Transformer is standard part from Wurth. Any ideas?
Thank You in advance