Part Number:TPS23754
What appears to be the negotiation phase happens and the supply starts to regulate then turns off.
The mystery is that there are other boards from the same lot that function properly. About 20% have this issue.
Design follows PMP5236 RevA including the layout (see images below)
See attached pdf schematic.
Measurements taken from board with no load/ no regulation beyond the 12V output. Also tried attaching a 100ohm resistive load to the 12V.
The other phenomena is that the 12V output does not rise to 12V but regulates below @5V before falling to 0 at the 350 ms time.
Yellow trace is voltage and blue trace is current (10 ohm resistor)
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View from top
View from bottom
Top view Red top traces
Bottom view Blue -Bottom traces
