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TPS5420: TPS5420 in Fly-buck configuration

Part Number: TPS5420
Other Parts Discussed in Thread: TPS54308, LMR33630, LM5019, LM5018, LM5017, LM5161, LM5160, TPS54160


I was just wondering around to see if TPS5420 can be used in Fly-buck topology (with coupled inductor) to have isolated DCDC output.

Is it possible to use TPS5420 ?

If possible, then any reference design for that ?

If not possible, then I would like to know the technical reason behind it.


  • Hi,

    It is not possible to use TPS5420.

    If we are putting heavy loads on the secondary side, the primary side current can go negative. That means we can only use synchronous buck for the fly-buck configuration.

    Best regards,


  • Ahh, its synchronous buck mechanism which will make Fly-buck possible.

    Thanks a lot for  the clarification.

    What about LMR33630 / TPS54308 synchronous buck converter?

    Can it be used for the said purpose ?

    Warm regards,

  • Hi,

    For LMR33630, at light loads, the mode changes to PFM. If we are putting heavy loads on the secondary side, the primary side current will go negative. Therefore, LMR33630 can't be used as fly-buck in this case.

    Theoretically, TPS54308 can be used for fly-buck. But we do recommend LM5017, LM5018, LM5019, LM5161 and LM5160 for fly-buck since we have typical application report for this case.

    Best regards,


  • Hi Wandy,

    Thank you very much for your valued reply.

    It make me better understand about flybuck thing. And I am going to select LM5161 for my application to start with practical exploration.

    I would like to ask about TPS54160. I came through this application report :

    Which is depicting TPS54160 in split supply application, seems similar to flybuck (using coupled inductor) but non-isolated.

    Here, as far as I understood the datasheet, TPS54160 have neither synchronous regulation feature nor it supports forced CCM mode. Then how it is feasible to use TPS54160 for this particular application with coupled inductor ?

    Though the last reply clarified the confusion I am having to choose the right component for flybuck application, This question is just to enhance my understanding.


  • Hi,

    The topology of the application note is inverter with coupled inductor, not a fly-buck.

    Best regards,


  • Hello,

    Glad to hear from your side.

    I think I need to relearn the fundamentals about all these topologies.

    Anyways, thanks a lot for your reply.