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TPS23758: Smaller Transformer?

Part Number: TPS23758
Other Parts Discussed in Thread: TPS23753A, TPS23755

Hi, we are hoping to use TPS23758 in a very space constrained POE design. The transformers used in the reference design are too large, specifically in Z height. 

In an effort to reduce transformer size, we may have to remove the secondary bias winding and go for a non-synchronous topology (similar to this one https://www.coilcraft.com/getmedia/63e9d40b-d0fb-40b3-897d-674278216439/pa6340.pdf used in a TPS23753A reference design).  

(1) Any estimate on the efficiency reduction we would see in this topology? 

(2) Are there any concerns aside from reduced efficiency (load regulation, stability, etc.) that going non-sync could affect? 

Thank you! 

  • Hi Emma,

    Thanks for reaching out.

    (1) Any estimate on the efficiency reduction we would see in this topology?

    Assuming you have 5-V, 2.3-A output, the diode will have ~2.3A x Vf loss when diode is forward bias, where Vf could be ~0.5 V. Considering the duty ratio, you could have 2 - 8% efficiency drop at 13W power. 

    (2) Are there any concerns aside from reduced efficiency (load regulation, stability, etc.) that going non-sync could affect?

    To use a non-synchronous topology, please use TPS23755 instead of TPS23758. Their CP pins are internally different for sync-FET and diode on sec side. You can check TPS23755EVM for your reference and make it a 5-V version.

    Best regards,

    Diang