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51W PoE+ PD

James Godfrey
Prodigy 10 points
Other Parts Discussed in Thread: TPS2379, TPS2378

Hello,

I would like to design a PoE+ PD Interface that can use all four pairs in order to get 51W while still maintaining 802.3at compliance ( which I *believe* is possible ).

I will be using a 3rd party isolated DC-DC converter after the PD Interface, so don't need a DC-DC Controller.

Do I need to use two PD Interfaces in parallel for each of the Mode A and Mode B pairs, or can I just use one PD Interface with each of the Mode A and Mode B OR'ed using diode bridges ?

If so, what PD Interface would you recommend ?

Jim Godfrey

  • 0
    TI__Mastermind 42795 points

    There can be a couple of ways to do this from a hardware point of view. Method #1 uses two PD controllers (dual TPS2378's for example) and method #2 uses a single TPS2379 with boosted current limit. In method 1, the first pair set within the ethernet cable to discover, classify and then power on would back-bias the second pair set's diode bridge. ORing diodes in the RTN legs of the TPS2378's can avoid this problem so the second pair set can also discover, classify, and power on (assuming the PSE supports this 4-pair method). For method 2, there would need to be some further communication between the PD and PSE (such as LLDP) after the first pair set powered on. This communication would tell the PSE to enable power to the second pair set.

  • 0 in reply to Eric Wright
    TI__Expert 7990 points

    Depending on how custom a system you want to make, you might also get some ideas here: http://www.ti.com/litv/pdf/slva498.  This app note talks about the second implementation shown above.

    Phihong  makes special high-power PSEs that would work with the PD implementation.  http://www.phihongusa.com/