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Original question:

TPS23756: TPS23756 circuit

TPS23756: PCB review

Shuang Feng76
Expert 3280 points
Part Number: TPS23756
Other Parts Discussed in Thread: TLV431A, , PMP40514

Could you please help customer to check the POE circuit.

Currently the output is zero to GND.

Hope for your PCB review and solution.

have a nice day.

  • 0
    TI__Mastermind 21320 points

    Hello Shuang Feng,

    I have some comments on the schematic:

    - the sync FET on the primary side has a 10k ohm resistor on the gate. The typical value is 10ohm, not 10K. This is probably causing a massive delay or completely inhibiting the FET to turning on, which is contributing to the issue. 

    - the opto feedback resistor divider (R43 & R50) create a 2.4V reference for the TLV431A. The max threshold for the reference voltage is 1.25V, so it is railing. 

    - I would also strongly suggest adding a TVS diode on VDD-VSS such as SMAJ58A.

    For your reference, I would highly encourage the customer to follow the PMP405414 design. It uses the TPS23756 and is an active clamp forward with 12V output. Since it is a proven design, I see no reason not to directly copy it. 

    If this post answers your question, please indicate so by marking this thread as resolved. Thank you.

     

    Regards, 

     

    Michael P.

    Applications Engineer

    Texas Instruments 

  • 0 in reply to Michael Pahl
    TI__Expert 3280 points

    Hi Michael，

    Thanks for your comments. I will update when I get the feedback.

    About the PMP405414 design, could you share it to me?

    I could not search it on our website and I did find it.

    thanks for your sharing and supports.

  • 0 in reply to Shuang Feng76
    TI__Mastermind 21320 points

    Hello Shuang,

    Typo on the design number: PMP40514 

    Added an extra 4. 

    For future reference, PoE reference designs can be found here: http://www.ti.com/power-management/power-over-ethernet-poe/powered-devices/reference-designs.html#search?famid=664

    And if a part is mentioned, like the TPS23756, typically the "Design & Development" tab will have EVM's and reference designs that use that part. 

    If this post answers your question, please indicate so by marking this thread as resolved. Thank you.

     

    Regards, 

     

    Michael P.

    Applications Engineer

    Texas Instruments