I found that you set the brown in voltage at 12V , but UCC28780 needs around 20V input to start switching.
I think that UCC28780 is not suitable for your application.
if the input spec is 25~40Vdc(even at brown in voltage) , you can refer the…
Part Number: UCC28730 Other Parts Discussed in Thread: PMP9009 , , Hi All,
My customer is designing an isolated power supply independently from battery for a forklift application.
I was asked to find a demoboard with below specs for the power part: