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LM5177: Power inductor selection

austin.chen
Prodigy 200 points
Part Number: LM5177

Hi TI,

I try to use LM5177 to implement our buck-boost power system.

But the calculate result is different between WEBENCH and excel calculator

Could you give me some comments about which one should I follow?

WEBENCH: 6.8uH

Excel Caculator: 1.4uH

And about the parameter ripple curent in Excel calculator, why the ripple current becomes larger with higher Vin.

Should I choose the inductor I-sat reference to which factor?

LM5177_9_48_12_6.pdfAMR_LM5177 Buck-Boost Quickstart Tool V1_0_9.xlsm

  • 0
    TI__Guru 58641 points

    Hi Austin,

    please use the excel calculator for the component selection.

    Inductor saturation should be selected based on the highest inductor current - based on the attached sheet this would be 45A.

    Also add some margin for the inductor.

    With a sense resistor of 3mOhm the over current protection would only trigger at 45 A- so with a larger sense resistor the saturation current can also be selected lower

    The ripple becomes higher for large Vin as the operatio is more pushed on Buck mode.

    (You can use the power stage designer to visualize this operation and the current in the inductor in a very nice way: 

    POWERSTAGE-DESIGNER Design tool | TI.com )

    Note: with the selected inductor you have a very large loss in Buck mode with 48V Vin

    Another option for the selection of the components could be 3.3uH and 3.5mOhm sense resistor.

    Best regards,

     Stefan