# External Wall Adapter Detection in MP8007?

I am reading the datasheet of MP8007. I found ambiguity in section Wall Power Adaptor Detection and Operation on Page 16. After reading the section, i am not able to understand how IC will differentiate between voltage from Adapter and PSE. Consider the equation given below:

Considering the example given in Page 20 under section Wall Power Adaptor Detection Circuit (Radpup = 3K, Radpdown = 8.06K and Vdadp3 = 30V), the IC can safely accept voltages from 38.48 to 53.98 V (even more than that).

Now, I am confused how will the IC gets to know that voltage is from Wall adapter or from PSE? Because PoE voltage range is from 44 - 57V and since, there is common voltages between adapter supply and PSE power supply and the wall adapter power is also applied at Vdd pin of IC (as with PoE).

The detection circuit is given below:

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.

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.