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TPS23756: transformer recommendation

Frank Xiao
Genius 12055 points
Part Number: TPS23756
Other Parts Discussed in Thread: TPS23751, PMP11254

Hi team,

My customer is using TPS23756 now, could you please recommend the transformer based on the requirement below.

VIN=37~57V，VOUT=12V/1.67A (20W)，Fs=250kHz，Dmax<.50%.

Below are the recommended EFD20 transformer.

Do we have the mathcad or excel about how to select the transformer?

   

Thanks.

  • 0
    TI__Mastermind 40100 points
    Hi Frank,

    Do you know where the 37V min input comes from? Are they trying to stay within the PoE standard? Note for this 20W solution a Type 2 PD's voltage range is 42.5V - 57V.

    Note also for a 12V Type 2 solution, we would recommend a flyback solution. What is the efficiency spec of customer? Also with an EFD20 transformer it sounds like a flyback solution. Why design with the TPS23756 (dual gate drive) when there is TPS23751 (single gate drive for flyback topoogy)?

    Regards,
    Darwin
  • 0 in reply to Darwin Fernandez
    TI__Genius 12055 points

    Hi Darwin,

    Thanks. Input 42.5-57v is fine. The TPS23756 is in the device library. They prefer flyback. No special efficiency requirement and no need for the sync rectifier. Whether the EFD15 is fine here? Could you please share some design tools?

  • 0 in reply to Frank Xiao
    TI__Mastermind 40100 points
    Hi Frank,

    I recommend looking at the below app note that goes over a non-synch flyback. It also goes over simple calculation to size the transformer.
    www.ti.com/.../slva305c.pdf

    Note that we do not have tools for specific transformer design calculator. Usually I just let transformer vendor know my power spec and topology. However below is a general magnetic design paper for flyback.
    www.ti.com/.../slup127.pdf

    For a 20W solution, EFD15 is very close to the max power. It probably gets too hot. I would recommend EFD17 or EP13+ core.
    I recommend looking at PMP11254 and use a similar power stage with the TPS23756 IC.