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LMR50410-Q1: Output Capacitor Caculation

Yuanzhao Yang
Prodigy 30 points
Part Number: LMR50410-Q1

Hi all,

 In datasheet section 9.2.2.5, it mentioned a part of output ripple is "caused by the inductor current ripple charging and discharging the output capacitors", and the following equation is given. I had some trouble understanding the coefficient of 8 in the denominator, what is the meaning and reason to put it here?

Also, in the next part it gave another equation to calculate the output capacitor when large current steps exist.

I can see the 8 on the numerator stands for 8 clock cycles, but what is the point to multiply by 1/2？

One more thing,

are these two equations derived from the Q=C*V=I*t?

Many thanks,

Yuanzhao

  • 0
    TI__Mastermind 30820 points

    Hi Yuanzhao-san,

    I am not sure to how these equations were derived.

    You maybe able to find some academic papers online that go over the derivation.

    For the first equation, that relates to output ripple, the second, that relates to load transient.

    You should also consider output capacitance needed for stability. That can be determined via webench.

    The max of all three is what you should choose for your design.