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TPS23756: review schematics for PD 25.5W

Henry Wang3
Genius 3445 points
Part Number: TPS23756


Hi Sir,

My customer want to use the TPS23756 for PD 25.5W on the new project, could you please help to review the attached schematics?

BTW, does there have the design guide for selecting the switching transformer (how to calculate the inductance value, winding of the transformer?)

Design condition: 52V-in (30W input), 12V-out (PD 25.5W, PD maximum support up to 30W)

PD_0408.pdf

  • 0
    TI__Mastermind 37111 points

    Hi Henry,

    Thanks for reaching out.

    We will review the schematic and get back to you by Wednesday US time.

    Best regards,

    Diang 

  • 0 in reply to Diang Xing
    TI__Mastermind 37111 points

    Hi Henry,

    Thanks for your patience. Please find the comments below:

    1.PPD is usually connected in the middle point of a resistor divider to set the turn-on voltage when with a passive PoE injector. PPD threshold is only 1.55 V, which may cause PD turn on at too low VDD-VSS input voltage and fails the PSE detection/classification.

    2.The classification resistance (137 Ohm) is for Class-2. Please check if its max power needs to be 25.5W.

    3. The output capacitance could be too large for 12-V voltage and Class-2 or -4 power. Too high output capacitance may cause PSE overpower protection at start up. Normally 100 – 200 uF should be enough.

    4.SMA packaged switching diode may be to hot during switching. Better to use one with larger thermal pad.

    Best regards,

    Diang