Dear Darwin
With respect to:
"For the inrush spec you refer to, the PD must finish charging the VDD-RTN capacitance before it can do normal current limit operation; otherwise, the PD will go into thermal cycling. The converter or the load should not be ON at initial startup so the PD can get out of the inrush current limit state. However, referencing the adapters to RTN will bypass this (as another consideration)."
Please, can you confirm this:
1) If I don't need the PoE classification and I want to use the TPS23756 as a simple Flyback converter with wide range of input (10.8VDC - 50VDC), then It's better OR'ed my 2 power supply (priority and backup) bettween VDD1 and RTN with:
-VDD and VSS unconnected( left float)
-DEN, CLS and PPD left float?
If it's true:
2) The TPS shoud be work instantly at power the circuit in VDD1/RTN (don't care with inrush current, thermal cycling, etc) ?
By the way, My TPS was working fine with VDD1/RTN (backup supply) but today in the morning can't work and Vc = 2.2 V... Vout=0V
But, by the night, I test again without load, and by a moment, the Vout=12V for a minutes... and then, Vout= 0 V, Vc = 2.2V
If 1) and 2) , were true, Vc always be ~9Vdc?