External Wall Adapter Detection in MP8007?
Now, I am confused how will the IC gets to know that voltage is from Wall adapter or from PSE?


The datasheet is really unclear on this, but I don't think that's the purpose of the power adapter detection circuit.

AFAICT, the only purpose of power adapter detection is to allow the switching regulator to start up without going through the PoE negotiation process.



From comments:


  what will happen when user plugs in adapter when PSE is already powering the PD


Not much. With diode-OR, one or the other will continue to power the regulator, depending on which one has the higher voltage.


  or vice-versa?


Again, not much. But in this case, the PoE negotiation will never occur, so the PSE will never enable power on the line. The external adapter will continue to supply the regulator.

If you subsequently unplug the adapter, then the regulator will shut down for a short period while the PoE negotiation occurs.


  What's your views on MP8007?


I have no views. You asked a question, I looked at the datasheet and gave you my interpretation of what I found.