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LM5152-Q1: LM5152QRGRRQ1　Regarding the capacitance of css connected to the ss pin

teruyoshi takahashi
Prodigy 50 points
Part Number: LM5152-Q1

Hello

Please tell me about the capacitance of Css connected to the SS pin of LM5152-Q1.

In the simulation model, 50nF was connected, but when I changed the capacitance to 0.1uF, the HO/LO operation was no longer observed.

What kind of behavior changes by changing the Css capacity?

Best regards,

takahashi

  • 0
    TI__Genius 15755 points

    Hello Teruyoshi,

    Thanks for reaching out to us via e2e.
    May I please fist ask you to properly fill in your account information. I see question marks instead of your name.

    The size of the capacitor that is connected to the SS pin defines the Soft Start time where the current of the converter is limited to avoid too high inrush currents.

    The Soft-Start pin is providing a very small current which is used to charge the externally connected capacitor.
    Then it is monitoring the voltage that is building up across that capacitor.

    When you are using a capacitor with an inner parasitic parallel resistance / a high leakage current, the current which is driven by the SS pin will not be high enough to charge the capacitor.

    Please verify that capacitor and maybe replace it with a different one with low leakage.

    Best regards
    Harry