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LM51581-Q1: boost converter inductor and capacitor selection confusion in application note

ASWIN K
Prodigy 20 points
Part Number: LM51581-Q1

Tool/software:

In the LM51581-Q1 boost converter design application note, how was the inductor RMS current calculated as 3.6 A? Also, the minimum output capacitance Cout_minC_{\text{out\_min}}Cout_min​ was calculated to be 3.8 µF, but 28 µF was selected—why was such a large value chosen? Additionally, the schematic includes two 100 µF capacitors at the output. Why were they added, and how was their value determined?can you please clarify this?

  • 0
    TI__Guru 65450 points

    Hello ANWIN,

    Today is a public holiday for all experts of this device. Please expect an answer by tomorrow.

    Best regards,
    Brigitte

  • 0
    TI__Expert 4090 points

    Hi Aswin,

    Thanks for using the E2E forum.

    The RMS inductor current is approximately equal to an average inductor current which is equal to the input current. 

    Regarding the Cout cap, it is recommended to select the output cap value higher than the calculated one because the cap value derated based on the voltage applied. Therefore higher value is selected for worst case scenario. 

    The highlighted output caps are not 100uF they are 100nF which are the decoupling caps.

    Moreover, the 100uF caps are DNPs. They are added to provide flexibility to customer to change the design.

    Best Regards,

    Hassan