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TPS23756: no handshake issue

Tommy Tzeng
Genius 4805 points
Part Number: TPS23756
Other Parts Discussed in Thread: BOOST-PSEMTHR-007, TPS23881EVM-008, USB2ANY

Hi Sir,

this is the customer final version schematic, but currently can' to handshake with the PSE side, is there something issue with this shcematic?

and attached the BOM list for this shcematic.

SCHEMATIC1 _ 13_PoE PD.pdf

  • 0
    TI__Genius 15951 points

    Hi Tommy,

    Thanks for the follow-up. The schematic looks good to me.

    Here is some suggestions about the handshake failure:

    1.What PSE did you use? Did you use the TI's GUI (TPS2388x) which would show the handshake fault reasons (an example is shown below)?

    2. Could you provide the VDD-VSS voltage and input current (one of the twisted pairs) waveforms during handshake? Then we could know it failed during detection, classification, or other period.

    3. Try to short the ferrite beads (PFB4, 5, 6, 7) which might cause detection resistance measurement error.

    4. There is no soft startup circuit at the secondary side. I am wondering if there could be something at startup caused the overcurrent protection of PSE. We could evaluate this after we have the waveform of #2. 

    Best regards,

    Diang

  • 0 in reply to Diang Xing
    Genius 4805 points

    Hi Diang,

    customer reply as below:

    2. Could you provide the VDD-VSS voltage and input current (one of the twisted pairs) waveforms during handshake? Then we could know it failed during detection, classification, or other period. ==> Currently using powersupply to supply 54V at the PL2 end not supplied by the PSE should not be can to measure handshake.

    3. Try to short the ferrite beads (PFB4, 5, 6, 7) which might cause detection resistance measurement error.==> PFB4~7 have been replaced 0ohm

  • 0 in reply to Tommy Tzeng
    TI__Genius 15951 points

    Hi Tommy,

    Thanks for the response.

    2. Could you provide the VDD-VSS voltage and input current (one of the twisted pairs) waveforms during handshake? Then we could know it failed during detection, classification, or other period. ==> Currently using powersupply to supply 54V at the PL2 end not supplied by the PSE should not be can to measure handshake.

    If the power supply is used at PL2, can the PD part be powered? If the PD can be powered on and work well at this condition, the downstream DC/DC circuit should be good. 

    3. Try to short the ferrite beads (PFB4, 5, 6, 7) which might cause detection resistance measurement error.==> PFB4~7 have been replaced 0ohm

    Besides the ferrite beads, could you also double check the pin of the T1. The common mode chokes are normally at the data side (not at the date & power mixed side). 

         

    I will close this thread for now as we have not received your reply for 3 months. Please open a new thread if you have any further related questions.

    We would recommend to use TI's GUI (TPS2388x) for your future detection/classification debugging. The detailed information is listed in below.
    TI’s PSE Hardware:
    1). BOOST-PSEMTHR-007 (you can request sample)
    2). TPS23881EVM-008 (you can request sample)
    3). USB2ANY Interface Adapter (you need to purchase one)
    Software:
    1). Download: www.ti.com/.../slvc772
    2). User guide: www.ti.com/.../slvubp0a.pdf

    Best regards,

    Diang