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LM3481 or LM5022 for SEPIC ?

Kevin Weng
Prodigy 60 points
Other Parts Discussed in Thread: LM5022, LM3481, LM5118

I need a DC/DC converter, the input voltage is 18 ~ 36 Vdc, and output voltage is 24Vdc / 3A(avg) ~ 5A (pk).

I choose the SEPIC topology, and search TI product,

I found 2 ic: LM3481 and LM5022, it seems could use in my requirement.

but I don't know what is the best solution for it ?  May someone give me a suggestion ?

or do it have AppNote for LM3481,  because I can find the AppNote for LM5022. 

Thank you !

  • 0
    TI__Expert 3545 points

    Kevin,

    I'm not very familiar with the LM3481, but I do know the LM5022 and it can be used as a SEPIC.  There is not a Application Note for the LM5022, but I have attached an article that should help.

    TErry5873.sepic2.pdf

  • 0 in reply to Terry Allinder
    Prodigy 60 points

    Hi, Terry,

    Thank you for your reference! it's very useful for me.

  • 0
    TI__Expert 3950 points

    Hello Kevin,

    both the LM3481 and the LM5022 can work for your application.

    The main differences between the two parts are the compensation since the LM5022 uses a regular feedback error amplifier while the LM3481 uses a transconductance amplifier which in most cases allows an easier compensation, and the input voltage range.

    Anyway I would not use any of those parts but i would use the LM5118 which is a four switch buck-boost. The power is not that low and the current is pretty high, if you want to use a SEPIC configuration you will need a big amount of sepic capacitors at high voltage.

    Regards,

    Giuseppe

  • 0 in reply to Giuseppe Pinto
    Prodigy 60 points

    Hi, Giuseppe,

    Thank you so much for your information. 

    I saw a document in TI about using SEPIC topology for 12V/4A output.
    and its sepic capacitors are approx. 10uF/50V (4.7uF * 2).
    what do you think how many capacitance of sepic capacitors need use in my application ?
    (there're few information talking to capacitance of sepic capacitors) 

    and if I use  2 switch buck-boost in my application.
    In your experience, which efficiency of these topology between buck-boost and SEPIC will be higher ?
    Thank you ! 

    Best Regard,

    Kevin

  • 0 in reply to Kevin Weng
    TI__Expert 3950 points

    Hello Kevin,

    the efficiency is actually comparable but the SEPIC is tougher to compensate and has two inductors but it uses only one mosfet and one diode

    The LM5118 will implement only 1 inductor and it ie easier to compensate but it will use two mosfets and two diodes

    In any case they both can work for your application.

    Regards,

    Giuseppe