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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:

enter image description here

Where, Vadp is adaptor voltage, Vdadp3 is the zener voltage, Radpup and Radpdown are the AUX divider resistors from adaptor power.

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:

enter image description here

enter image description here

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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.

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  • \$\begingroup\$ I think IC will enable PoE when it detects detection signature voltages and enable AUX when it doesn't detect the detection signature. I am confused what will happen when user plugs in adapter when PSE is already powering the PD or vice-versa? \$\endgroup\$
    – abhiarora
    Commented Oct 3, 2018 at 17:24
  • \$\begingroup\$ What's your views on MP8007? Can you suggest better? It doesn't have low-side MOSFET swtich. I want to operate as buck converter and PD. \$\endgroup\$
    – abhiarora
    Commented Oct 3, 2018 at 18:27
  • \$\begingroup\$ See edit above. \$\endgroup\$
    – Dave Tweed
    Commented Oct 3, 2018 at 18:40

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