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LM5022 - Help with SEPIC Control Loop Compensation requested.

Paul Jukes
Prodigy 20 points
Other Parts Discussed in Thread: LM5022

Hi.

I am attempting to design a SEPIC converter using a LM5022. Unfortunately I have not been able to find any examples (or tools) that will assist me in designing the Control Loop Compensation. The Webench does not appear to provide a SEPIC topology for the LM5022, and the data sheet contains a Boost converter design only.

I question whether the formulae for the Control Loop Compensation of a Boost converter can be used for a SEPIC design? I fear that the extra inductor and coupling capacitor of the SEPIC will require quite a different solution to that for a Boost converter.

I would appreciate it if someone could point me at, or provide me with the formulae and /or a procedure for designing the SEPIC control loop compensation circuits.

Thanks In advance.

  • 0
    TI__Expert 3545 points

    Paul,

    I have attached an article by Ray Ridley on  SEPIC control loop design, I hope this helps.

    Terry1665.Sepic Analysis.pdf

  • 0 in reply to Terry Allinder
    Prodigy 20 points

    Hi Terry

    Thanks for the article. Sadly, we just can't justify the time it would take to perform an analysis like that described. A SEPIC topology would suit our application very nicely, but we really need a "design by numbers" approach for us to produce the product in our desired time frame.

    To be able to use the Webench would be perfect for us, but when we try using it for the LM5022 we get a "Design cannot be created" error. When I follow the "Show why parts were not found" link I'm advised that Webench "Can't find any suitable couple FET/diode for the design" when using the LM5022.

    By following the usual criteria for selection of SEPIC components, we're pretty sure we've got a design that'll work with the FET and diode we've chosen, but without the formulae for the Control Loop Compensation we're still in no-man's land.

    FYI, our application requires:

    9V =< Vin =< 30V;  Vout = 24V;  Iout = 6A

    I know Webench will work for a lower output current, so the required formulae must reside somewhere. Is there any way you can provide the Control Loop Compensation formulae used by Webench? A copy of the full design procedure and formulae used by Webench would be even better, if it were available.

    Thanks for your assistance to date, and thanks in advance for any additional information and support that you can provide.

    Regards.

    Paul