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LM3481: LM3481

Lars Alfredsson
Prodigy 50 points
Part Number: LM3481
Other Parts Discussed in Thread: LM5155

Hello,

I am designing a SEPIC converter with input voltage ranging between 9 and 100 VDC. The output shall be fixed at 48 VDC. Current load on output is up to 2A.

My question is if I can use the LM3481 with a separate 12V supply to the Vin pin (since the maximum voltage of the LM3148 is 48V), and then connect the 9-100V supply to the inductor/MOSFET on the outside? I,e he Vin pin will be separated from the 9-100 V.

I guess the question comes down to if the Vin voltage is used as a reference for the regulation inside the chip, or if it is just used for logic and MOSFET driver  supply.

Thanks in advance.

Lars 

  • 0
    TI__Mastermind 30975 points

    Hi Lars,

    Thanks for considering the LM3481 in your design. You can power the LM3481 with a separate supply to the VIN pin and then have a separate input to the inductor. This can also be done with the LM5155, which is an improved version of the LM3481.

    Thanks,

    Richard

  • 0 in reply to Richard Fu22
    Prodigy 50 points

    Hello Richard,

    Thank you for a quick reply. Your answer solved my question.

    I would very much like to consider the LM5155 since is it newer and also slightly cheaper. However I cannot find any application note related to SEPIC design. And the datasheet just mentions SEPIC but does not give any design advice whatsoever. This is currently preventing me from choosing this component.

    Is it perhaps so that the AN-1484 (which is not linked to the LM5155 but is linked to the LM3481) is applicable?

    If not, where can I find design guidelines for a SEPIC using the LM5155?

    Thanks

    /Lars

  • 0 in reply to Lars Alfredsson
    TI__Mastermind 30975 points

    Hi Lars,

    AN-1484 is a good starting point for the design since the design of the SEPIC power-stage remains the same regardless of controller. 

    Thanks,

    Richard