Do you have oscilloscope waveforms showing what the UCC28600 pins are seeing? Can you please send the schematic and design calculator that was used for the design? If you increase the input voltage, will it start? There are several reasons why this may be happening, it could be noise triggering a perceived fault condition, it could be the primary inductance is too large for the application so the on-time is exceeding the internal QR-done signal. Waveforms, schematic, and design details will help solve this issue.
↧