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TPS2379: LLPD not working on POE+ IC

mfar
Prodigy 50 points
Part Number: TPS2379
Other Parts Discussed in Thread: TPS23754

We have a customer with our POE PD device which has a TPS2379 IC, they are having the following issue. In all the below situations they are using the Cisco PSE.

  1. Communicating to our device with LLPD turned on the PSE, our POE PD receives only 15.6watts(POE) max not 30 watts(POE+).
  2. Communicating to our device with LLPD turned off the PSE, our POE PD receives only 15.6watts(POE) max not 30 watts(POE+).
  3. Communicating to our device with POE+ forced on PSE port, our POE PD finally receives 30 watts.

Can you let me know how we can get situation 1 and 2 to output max 30 Watts(POE+).

 

  • 0
    TI__Mastermind 41760 points
    Hi mfar,

    Please see e2e post below as this also applies to the TPS2379.
    e2e.ti.com/.../2617408

    In order to get 1 and 2 to output higher power, the microcontroller on the PD must communicate with the PSE through the ethernet data lines and negotiate higher power.
  • 0 in reply to Darwin Fernandez
    Prodigy 50 points

    Darwin in your comment below from the link you sent, would it mean this product Cisco WS-C3650-48PS doesn't Type 2 hardware classification? If we want to support LLPD, would our device have to boot to a lower power mode initially and do the LLPD initiation and afterwards fully turn our device ?:

    Your comment "The microcontroller is on the load end of the PD system and the MCU should be the one to initiate the data layer classification after detection and startup (if the PSE cannot do Type 2 hardware classification)"

  • 0 in reply to mfar
    TI__Mastermind 41760 points
    Hi mfar,

    I thought you were able to set it to hardware classification (situation 3) this means PSE can do hardware classification?
    For the IEEE standard a PSE can do either classification through the physical layer or the data layer (DLL). If DLL, then the PD must be able to communicate with the PSE.
    You are correct in that PD will power up to lower power mode first (13W) to power the MCU etc. Then the MCU can communicate/negotiate with the PSE for higher power (25W).
  • 0 in reply to Darwin Fernandez
    Prodigy 50 points
    Darwin,
    For situation 3, we have to in switch settings set"force" the POE port to be configured as a POE+ otherwise we can only get POE power, which doesn't seem like a hardware classification.
  • 0 in reply to mfar
    TI__Mastermind 41760 points
    That is correct, "force" probably means hardware classification for this PSE.

    My last post was trying to answer the question "would it mean this product Cisco WS-C3650-48PS doesn't Type 2 hardware classification?"

    The answer would be yes that PSE can do hardware classification if set to "force" setting. TPS23754 can handle this internally because it is hardware based.

    The other setting is LLDP which relates to situation 1 and 2 above and is microcontroller based so the end equipment system must handle this.