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TPS2372: AT PSE/POH PSE

Daniel Campano
Intellectual 470 points
Part Number: TPS2372
Other Parts Discussed in Thread: BOOST-PSEMTHR-007, TPS23880EVM-008, TPS23880

Hi All,

I'm testing the TPS2372-4EVM-006 evaluation module against several switches and injectors that we have in site. The TPS2372-4EVM-006 has been configured as Class 6 ( 51w at the PD). Every time I connect BT PD Class 6  to an AT PSE device it shows TPH = High, TPL = Low , BT = High, which I agree as it's a demotion case using an AT PSE.

There has been a case where an AT injector didn't turn on the BT PD Class 6. I had to set the BT PD  as Class 4 and then it  was capable to turn the PD on and  it was able to supply the full power needed by the application ( it is a 60w injector). I guess the reason is because it is an POH PSE, but it is not specified  in the injector datasheet ( or at least that is what I think). I guess this suggests that I need to set the capability to the end user to switch between Class 4 and Class 6  as POH  won't turn on if the PD is set to Class 6. I guess I'm not the first one on this situation, I'm thinking to use a switch to change between Class 6 and Class 4, but I guess there will be more solutions, any idea?.

Is it common for POH PSE  not to specify that they are POH?. Before the development of BT PDs and BT PSEs I can't find a reason to distinguish between AT PSEs and POH PSEs, is there any?.

If I give you the part number of the injector that I have mentioned could you confirm that it is a  POH injector?.

Thanks in advance,

Daniel.

  • 0
    TI__Genius 9230 points

    Hi Daniel,

    Your PSE injector supports 802.3at (30W) & non-standard 60W. The PSE did not recognize the PD configured for class 6 because the PSE does not support the IEEE 802.3bt standard. I cannot speak on the specific language used by your PSE manufacturer, but compliance with "IEEE 802.3bt" should be prominently noted in the marketing material.

    To test with class 6, we recommend using our BOOST-PSEMTHR-007 motherboard with TPS23880EVM-008 daughter card.

    For more information on the new "bt" standard, take a look at our blog & the video links at the bottom of the page: 

    Key considerations for designing with the new PoE standard
    Other Parts Discussed in Post: TPS23880 The Institute of Electrical and Electronics Engineers (IEEE) 802.3bt standard will publish in September 2018 and enable Power over Ethernet (PoE) applications…
    By in Technical articles > Power management


    Thanks,
    Tom Amlee
    PoE PD Apps Engineer

  • 0 in reply to Thomas Amlee
    Intellectual 470 points

    Hi Thomas,

    Thanks for your answer. I have tested a few 802.3at(30w) injectors and non-standard 60w ( with AT classification)  injectors and they get recognized by the development board. In those cases the TPH and TPL show high and low and I understand this as the PD Class 6 thinks that it is connected to a type 2 (802.3at)PSE. In the specific case of that injector TPH,TPL and BT are Low-Low-High, it means that is connected to a PSE++ or POH, this is one of the reason I was thinking it was a POH injector ( the other reason is that it just operates when the PD is class 4). 

    When a PSE is compliant with IEEE802.3at,  it should be recognized by a IEEE802.3bt PD, is this correct?.

    When you said that the PSE supports 802.3at( 30w) and non-standard 60w, can I understand that it is compatible ( it will work) with IEEE802.3at PDs but that it is not complaint with IEEE802.3at?.

     I haven see the video of working with non-compliant PSEs and it specifies that  a POH PSE will just recognize a BT PD if it is configured as Class 4 or less and TPH,TPL and BT will be low-low-high,knowing this, can we at least say that it behaves as a POH PSE?

    Thanks in advance,

    Daniel.

  • 0 in reply to Daniel Campano
    TI__Genius 9230 points
    HI Daniel,

    LOW-LOW-HIGH means a non-standard PSE is connected.
    Any time TPH-TPL is HIGH-LOW, respectively, a .at compliant (type 4) PSE is connected.

    In any case, the PD hotswap FET will turn on as long as the 36V VDD-RTN UVLO is exceeded. Based on the class signatures presented by the PD, the PSE makes the determination how much power to provide. Your PSE will not be able to provide more than class 4 power if only relying on hardware-based classification that is compliant.

    Regards,
    Tom Amlee
    PoE PD Apps Engineer
  • 0 in reply to Daniel Campano
    TI__Mastermind 41760 points
    Hi Daniel,

    If this thread is resolved, please click the resolve button so we can close this thread. Thanks for choosing TI!
  • 0 in reply to Daniel Campano
    TI__Genius 9230 points
    No problem, Daniel.

    If you are have found resolution to your issue or have no further questions, could you do me the favor of clicking the green "resolved" button the post that you found most useful? It helps me close the thread on my end.

    Thanks,
    Tom Amlee
    PoE PD Apps Engineer