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TPS2373: PoE and LLDP

Casey Kienzle
Prodigy 10 points
Part Number: TPS2373

Hello,

My name is Casey, and i work with a ODM company called Social Mobile.

We have developed a medical android based 22 inch device using the TPS2373 as part of a PoE board separate from the main board.

Our client who we produced this device for requires it to work with LLDP however, until now the device cannot successfully negotiate the power it needs  (31.1 watts). 

We are trying to work through this issue with our client but we have hit a wall and are now trying to sort it out.

Since the TI TPS2373 is the chip we are using for PoE we believe your team will be able to help us clear the issue up.

Below you will find the spec sheet for the exact chip we are using as well as a snippet from the port setup showing the issue.

Any help your team can give will be greatly appreciated.

Thank you!

2084.tps2373.pdf

  • 0
    TI__Mastermind 37121 points

    Hi Casey,

    Thanks for reaching out to us.

    Sorry that we do not have bandwidth to answer you today. Your question has been assigned to one of our team members. Please expect his reply tomorrow.

    Best regards,

    Diang

  • 0
    TI__Intellectual 1480 points

    Hi Casey, 

    It looks like your PD is configured for Class 4 power level. According to the 802.3at and bt specification, the PSE can source up to 30W for this power class and the PD is only guaranteed 25.5W power delivered. This is why you are not seeing the power levels needed. The PD hardware design will need to be modified to a class 5 PD. I would also check to see if the PSE is Type-3 capable and able to deliver the power you need.  

      

    Regards,

    Sai Gunda

  • 0 in reply to Sai Gunda
    Prodigy 10 points

    Hi ,

    Thank you for the feedback, it was very helpful.

    Our engineering team had a couple of questions regarding the reporting.

    Is it the 2373 chip that is reporting the class? Or would it be another piece of hardware?

    Can it be changed via the OS layer or is it a deeper layer that requires a change to report properly?

  • 0 in reply to Casey Kienzle
    TI__Intellectual 1480 points

    "Is it the 2373 chip that is reporting the class? Or would it be another piece of hardware?"

    The TPS2373 is a PoE powered device only and does not have a data link interface. This means that it can perform detection, classification, and accept power from the PSE on the physical layer only. It does not have the ability to send and receive ethernet data so the TLVs are being reported by another device. 

    "Can it be changed via the OS layer or is it a deeper layer that requires a change to report properly?"

    It cannot be changed through the OS layer and requires hardware (physical layer) modification of the PD circuit. To upgrade to class 5, you would need to modify the classification resistors and upgrade the design to a 4Pair power design. 

    This video goes into detail the physical handshaking process that TPS2373 uses: https://training.ti.com/poe-handshaking?context=1137930-1139676-1137928 

    Regards,

    Sai Gunda

  • 0 in reply to Casey Kienzle
    Prodigy 10 points

    Thank you again you are a godsend.

    We have reviewed and currently we only have one pair of resistors for classification and the TPS2373 only has one pair of PINs for classification.

    We are not sure how to enable 4 pairs, do you have any insight on this?

    Attached is the circuit design any help you can give would be amazing.

    Schematic

  • 0 in reply to Casey Kienzle
    TI__Genius 15275 points

    Hi Casey,

    Due to US holiday times, I will be taking over this thread as I am also part of PoE team. 

    Classification is achieved using the pair of CLS pins and truth conditions to negotiate power class. Please see table below for truth table and CLS resistors to select proper classification. I have circled Class 5 since it seems you will need Class 5 Power in order to meet your power needs of device,

    Per your schematic, it seems you are requesting Class 8 power which can only be acheived using 4 pair.

    Since you are requesting Class 8 power and not seeing full power need, I would suggest checking the capabilities of the PSE you are testing with. It seems the PSE is a Type 1 or 2 PSE and can not support 4 pair power. Therefore, your power will be limited to Class 4 which is 30W at the PSE and 25.5W at PD. 

    Enabling 4 pair power on the PD is a slight hardware modification, however if the PSE can not support 4 pair power then you will not be able to achieve this. 4 pair power on the PD can be configured on the hardware from the RJ45, Data transformer, and recitifcation circuit. Please see below example from TPS2373-4EVM-758.

    Very Respectfully,

    Brandon Beader

  • 0 in reply to Brandon Beader
    Prodigy 10 points

    Hi

    I hope you had a fantastic holiday and happy new year!

    Thank you for the reply! We have reviewed thoroughly and talked further with the engineering team.

    Their reply is that the design we used is based solely on the same reference you provided in the above post however it is still not reporting the class 5 it needs. 

    Attached you will find that the spec sheet for the PoE board and the general schematic.

    We are unsure where to go from here or how to fix the issue.

    Any help you can give is greatly appreciated.

    Thank you!

    WC-PD45L120 Data Sheet.pdf

  • 0 in reply to Casey Kienzle
    TI__Genius 15275 points

    Hi Casey,

    Happy New Year!

    Yes it seems your design is okay. Your device is requesting Class 8 power which can only be sourced from a Type 3 or Type 4 PSE. Type 3 and Type 4 PSE support 4 pair power which is what is needed to supply anything >30W. The PSE you are testing with is a Type 2 PD which can only support up to Class 4 power (2-pair) which is not enough to meet your requirement. 

    In order to test this board, you will need an IEEE802.3bt standard PSE. I recommend using our TPS23881EVM in order to achieve this, which is an IEEE802.3bt device capable or supply up to 90W over 4 pair power. For this EVM you will need TPS23881EVM-008 daughter card, BOOST-PSEMTHR-007 mother board, USB2ANY for I2C, and TPS2388x EVM GUI along with SRAM v07 which can be found on TPS23881 product page.

    Can you attach your full schematic so I can review if your device is set up for 4 pair power? I have sent you a friend request which includes my email so we can setup a meeting if needed. Thanks!

    Very Respectfully,

    Brandon Beader