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TPS23753A: TPS23753A flyback design

Amina Bahri
Prodigy 90 points
Part Number: TPS23753A
Other Parts Discussed in Thread: PMP9175

Hey TI community!

For my PoE design I am using the TPS23753A PD and DC/DC controller with the help of the application note SLVA305C.

In the flyback converter design calculations, Vflyback min=20V (I assumed because the external adapter was used). In my case I am not using any adapter (just 37-57V from PSE) and my flyback transformer´s input voltage is in the range of 36-57V (I am using the NA6223 from Coilcraft). Therefore in my case, when using Vflyback min=36V in the transfromer design calculations, the Nps, Lprimary, ect are completely out of the targeted range.

any advices?

Thank you very much in advance,

Amina

  • 0
    TI__Genius 9230 points
    Hi Amina,

    I recommend rechecking the app note. We use the same process in the design of our EVMs.

    To clarify:
    When you specify Vflyback_min = 36V, are you getting different transformer calculations than similar to the NA6223 specs? Be certain that your output voltage & current is similar to the PMP9175 & PMP8896 designs (if you are intending to replicate those designs).

    http://www.ti.com/tool/PMP9175
    http://www.ti.com/tool/PMP8896

    Thanks,
    Thomas A.
  • 0 in reply to Thomas Amlee
    Prodigy 90 points

    Hi Thomas,

    Thank you for the quick answer. yes with Vflyback_min = 36V, the transformer calculations are far from the NA6223 specifications. It only works when I use Vflyback_min=Vadp_min. At the same time I know that NA6223 is suitable for the TPS23753A and for the voltage I need as output (and assuming I am adopting a class 3 type 1 PoE).

    My question is what should be the Vflyback_min value for the design calculations if no adapter is used.

    Thank you again!

    Regards,

    Amina

  • 0 in reply to Amina Bahri
    TI__Prodigy 70 points

    Amina,

    Thomas A is having Thanksgiving Holidays. He will provide some advice on next Monday.  Stay tuned.

    Regards,

    Manson

  • 0 in reply to Manson Chan
    TI__Genius 9230 points

    Hi Amina,

    I have just gotten back from holiday, so I am catching up.

    Quick answer to your last question: Vflyback_min without the adapter should be the minimum voltage for the PoE standard: ~36V, as you have it.

    So the NA6223 transformer specs make sense when you use a lower adapter voltage (12V) for calculation, even when the board does not go under 36V input?

    Nonetheless, I would give the NA6223 a try. Let me know if you have any issues.

    Best,
    Tom A.

  • 0 in reply to Thomas Amlee
    Prodigy 90 points

    Hi Tom,

    Thank you for your reply, I hopr you enjoyed your holidays.

    The calculations give perfect results when using the 24V adapter voltage (not with 12V though), except the fact that I do not use one. I wonder if these calculations apply only when using an adapter, or maybe Vin is different from Vin_flyback?

    However I also do think this transformer is suitable for my design and will use it for my prototype. Just wanted to understand more the design calculations.

    Thnak you!

    Regards,

    Amina