Other Parts Discussed in Thread: ATL431, UCC28780
I duplicated the PMP21639 reference design exactly and I'm checking the Vo (without USB-C cable attached). I matched every component used as well.
The issue is Vo is always 8VDC with no load and occurring on every board tested. If I add a small resistive load between Vo and SGND then Vo drops to the expected 5VDC. One of the tests I tried, I replaced R45 with a potentiometer that feeds the ATL431 REF pin and noticed that with no load the Vo does not change from potentiometer. But with a small load applied Vo starts to work as expected and changes with potentiometer. It seems the standby mode in UCC28780RTER is not working.
Also, is it possible to purchase a working PMP21639 that I can compare signals to?