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LM25116: Input Capacitor ripple current

nnn sato
Prodigy 230 points
Part Number: LM25116

Tool/software:

①In 8.2.2.6 of the datasheet, it says that the input ripple current is IRMS > IOUT / 2, but is it okay to estimate it at a value close to IOUT / 2?

Conditions:
Vin 24V
Vout 17V~10V
Iout 11A, 4A (2 circuit design)

Is it okay to estimate it at IRMS 11A/2=5.5A?

If not, how close can I get?

②Will the output function normally without the input capacitor?

  • 0
    TI__Mastermind 18685 points

    Hello,

    Please see the numbered answers corresponding to your questions:

    1. The Irms > IOUT/2 is OK to use when choosing capacitors with the proper RMS current rating. In order to select properly rated capacitors, make sure to follow the datasheet recommendation of selecting a capacitor with an Irms rating larger than IOUT/2.
    2. No, the device will not function properly. Input capacitors are required for the device to function. When designing the circuit, please make sure to follow all recommendations in the datasheet.

    Best regards,

    Ridge

  • 0 in reply to Ridge Lahti
    Prodigy 230 points

    In the case of ">", how far can I get closer to IOUT / 2?
    1 or 0.1 or 0.01 digits

  • +1 in reply to nnn sato
    TI__Mastermind 18685 points

    Hello,

    The equation Irms > Iout/2 is used as an estimation to properly size capacitors. For proper performance of the device, all recommendations in the datasheet must be followed.

    It is up to the user to decide how close to the margin the chosen external components are. It is also up to the user to validate that the design is functioning properly with the chosen components.

    Best regards,

    Ridge