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Nonstandard POE(PSE+PD) 50W

Lucifer
Expert 2600 points
Other Parts Discussed in Thread: TPS2379, TPS23861, TPS23861EVM-612, TPS2379EVM-106, TPS2378

We want to design a 50W POE (PSE+PD) solution and I learned that TPS2379 can support greater than 50W for powered device (PD) controller.

but regarding PSE TPS23861, Can I connected TPS23861 to TPS2379 for 50W application?

I found TPS23861EVM-612 have two non-standard ports which provided at J21 and J9 for four pair ports 1 and 2 (High Power capable ports) respectively,  so can I  connect J21 of PSE(TPS23861EVM-612) to  PD (TPS2379EVM-106) over Ethernet Cable driectly ?

Thanks,

  • 0
    TI__Mastermind 42795 points

    Please refer to the attached slideset (slide 2-4 for TPS2379EVM). Slides 6,7 show another method using a dual TPS2378 forced design according to SLVA625.

    Note that for the TPS2379EVM configuration, make sure to add the output load (~2kohm) in order to keep both PSE ports connected.

    TPS23861-TPS2379 4-Pair.pptx

  • 0 in reply to Eric Wright
    Expert 2600 points

    Dear Eric,


    1. thanks for your kindly reply.  I checked the slides and it seems there are two methods support 50W application. Could you give me some suggestion that which one is better?
    2. Moreover, according to the slide page 2, as long as I set up the parameter then, I can connected TPS2379EVM and TPS23861EVM together, is that right?

    3. what does you mean about TPS2379EVM adding  the output load(~2Kohm) ? could you please provide  reference circuit?

    4.One more thing , How fast is the transmission rate? Can TPS23861+TPS2379 support gigabit Ethernet?

    Thanks for your help

  • 0 in reply to Lucifer
    TI__Mastermind 42795 points

    Actually, there is ongoing PoE work for 4-pair high power within the IEEE. You can find information online ("BT" standard), but the planned power levels will exceed 50W. The two methods we describe here can also provide higher power but may not conform to the new standard.

    As far as a choice between the TPS23861+TPS2379 vs. TPS23861+TPS2378(2x), it might depend on whether or not you want to take a hardware only approach or whether you have a software engineer that can write some simple code to manage the TPS23861. TPS23861+TPS2378(2x) can provide a hardware only approach while TPS23861+TPS2379 will require some control over I2C for the TPS23861 (the TI GUI can already provide this simple control). In both cases, the slides provided used the real EVMs (TPS23861, TPS2379, and a dual TPS2378) along with the PI-Commander GUI to capture the graphics. It is easy to set up and test. The GUI and EVMs are available online.

    Regarding the DC load, the PSE must check whether enough PD loading is present and then remove voltage if loading falls below a threshold. SLVA625 http://www.ti.com/litv/pdf/slva625 provides a description of how the reference design provides the "maintain power signature" (or MPS from the IEEE PoE standard) for the connected port while the second (of a 4-pair system) is being configured to deliver power. See the "MPS" paragraph on pg 7 of SLVA625. The ~2kohm load on the output of the TPS2379EVM (between J4-1 and J4-4) provides a simple MPS for that configuration. A single PD should provide a minimum of 10mA loading to the PSE in order to maintain power. SInce this configuration uses 2 PSE ports (4-pairs) the PD should ideally load the PSE with >20mA. If the PSE port voltage is 48V, then 48V/20mA = 2400 ohms. Using 2kohm provides a bit more current so that the PSE port remains connected to the TPS2379 if the currents are not balanced (which is the case under low current and/or short ethernet cable conditions).

    Lastly, TPS23861 and TPS2379 can be used with any data rate supported by the IEEE PoE standard (the PSE/PD power insertion/extraction does not interfere with the data). This even includes 10G ethernet. The TPS23861EVM uses port jacks which are 1GBPS while the TPS2379 uses 10/100MBPS transformers on each pair for 1GBPS support.