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TPS23754-1: TPS23754-1 support DLLC(Data Link Layer Classification) or not?

Mark Chao
Prodigy 20 points
Part Number: TPS23754-1
Other Parts Discussed in Thread: TPS23754

Hi TI, member,

We utilized TPS23754-1 to design one Powered Device product, according to TPS23754-1 version I specification description, The PoE interface of TPS23754-1 support IEEE 802.3at Type-2 powered device (PD) such as Detection, Classification, Type 2 Hardware Classification.

But we got one filed feedback from our customer, they said our product didn't support fully IEEE 802.3at standard due to we cannot pass DLLC(Data Link Layer Classification) test including Link Layer Discovery Protocol
(LLDP). 

But I saw one discussion on TI Community, TI employee Martin Patoka siad: TPS23654 is a type 2 full implementation of Powerd Device including HW type 2 detection & LLDP)

Please help me check this question and provide your feedback to me. Thanks.

  • 0
    TI__Mastermind 40120 points
    Hi Mark,

    The TPS23754 PD controller, on its own, is able to do classification through the physical layer (hardware classification). LLDP is done through the data layer and NOT the physical layer which means you will need a micro controller on your PD system to implement LLDP and negotiate with the PSE (through the data lines) that the PD is requesting higher than Type 1 power.

    Please note on page 20 of the TPS23754 datasheet:
    "DLL communication is implemented by the ethernet communication system in the PD and is not implemented by the TPS23754."
  • 0 in reply to Darwin Fernandez
    Prodigy 20 points

    Hi Darwin,

    Thanks for your help.

    Due to we utilize TPS23754-1 to make our PoE PD design in our product and set Classification Resistor to 63.4 ohm for 802.at class 4 PD.

    We use Sifos PDA-300 Powered Device analyzer to validate our design, the test result is pass, we meet 802.3 at standard and we are Type 2 class 4 PD. Please see the appendix 1.

    Appendix 1_PoE PD test result with TPS23754-1.xlsx

    But it's only Type 1 and Type 2hardware classification verification.



    According to 802.3at-2009 standard 33.3.5 PD classifications description, Type 2 PDs implement both 2-Event class signature and Data Link Layer classification, please see appendix 2.



    Due to TPS23754 specification page13 overview description, the TPS23754 have a PoE that contains all of the features needed to implement an

    IEEE802.3at Type-2 powered device (PD) such as Detection, Classification, Type 2 Hardware Classification, and140-mA inrush current limit during start-up. Please see appendix 3.



    It's not match IEEE 802.3at-2009 standard, can you explain it to us? Thanks.

  • 0 in reply to Mark Chao
    TI__Mastermind 40120 points
    Hi Mark,

    Just to be clear. When the standard says PD, it really means the PD system (PD end equipment) while the TPS23754 is a PD controller (a part of the PD end equipment).

    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).

    Regards,
    Darwin