LM5023: Can't capture the first gate turn on pulse on an LM5023

Hi All,

I have designed a power supply around the LM5023. I am doing a sanity check before hooking it up to AC mains. The design is basically the same as the evalkit. I am only just powering the IC externally with a bench supply at 13.5V to check some waveforms but is doesn't even generate the starting gate signal. This doesn't seem right to me as it emulates the real startup scenario.

Any ideas as to why this may be happening?

Thanks,

Simon.