PMP20859: Disabling TPS2372 PoE controller completely.

Ian Middleton

Part Number: PMP20859
Other Parts Discussed in Thread: TPS2372

We have successfully implemented a dual PoE & external 48V input based on the PMP20859 reference circuit, which works fine. External 48V in only, works. PoE swapping over works no glitches, all fine.

In our next design we need the same again but the need the ability to disable one of the PoE power inputs, so that it its just plain 1G Ethernet.

Do we just pull the DEN pin low on the TPS2372 to completely disable it and prevent it taking part in any power control and Ethernet configuration messaging ?

over 2 years ago

0 Robert Taylor1 over 2 years ago

TI__Expert 6670 points

Hi Ian,

I have asked our PoE expert to help you out, please allow some time.

Thanks,

Robert

0 David Strasser over 2 years ago in reply to Robert Taylor1

TI__Intellectual 2530 points

Ian,

If you don't need redundant operation when this port is re-connected you can disable the port by pulling DEN low. If there is the possibility of a PSE being connected to this port, you should follow figure 10 of the slva306a applications note, splitting the detect resistor into two resistors and pulling the center tap to VSS. This will present an invalid detect signature to the PSE, preventing it from attempting to apply power. Also note that the pull-down is to VSS, so some type of isolation is required.

https://www.ti.com/lit/an/slva306a/slva306a.pdf?ts=1690914568422&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FTPS23753A%253FkeyMatch%253DTPS23753A%2526tisearch%253Dsearch-everything%2526usecase%253DGPN-ALT

If you want redundant operation when this port is reconnected, then external circuits are required.

Thanks,

David

0 Ian Middleton over 2 years ago in reply to David Strasser

Prodigy 100 points

Thank you, this is just the information I required.

This is for a common design that required 3 different manufacturer configured power sources:

- 48V external input, 2 off Ethernet connections non PoE.

- 2 off PoE Ethernet connections, either powering.

- 1 off PoE Ethernet input and 1 off non PoE Ethernet input.

We were intending to make and populate one PCB only and configure the variations of power inputs with configuration links, which would there for require disabling of the PoE circuitry by making links during production.

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PMP20859: Disabling TPS2372 PoE controller completely.