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CSD95377Q4M: Should I take the capacitance of pi filter into account when I design the input capacitors?

Part Number: CSD95377Q4M

Hi there,

I'm wonder if I should take the capacitance of the pi filter into account when I design the input capacitors. For 12V input for the VIN pin of CSD95377Q4M, I have a PI filter design as below. If I have 22uF*2+3.3nF*1 on the VIN pin, is the total capacitance just 22u*2+3.3n*1 or 22u*4+100n*1+3.3n*1? Thank you for your prompt response!

  • Hi Minkyung,

    I am not very sure about what exactly do you mean by "total capacitance".

    The Vin capacitors are needed for: 1. limit voltage ripples on Vin; 2. provide energy buffer for power stages during transient; 3. some Vin caps are placed very close to power stages to minimize the parasitic inductance. If you are try to limit voltage ripples on Vin during steady state operation, then yes, all components in the pi filter would help.  If you want to calculate the energy buffer during load transient, then the capacitance before inductor is less effective then the capacitance very close to power stage, because the inductance will slow down the energy transfer. Actually the capacitors placed around power stage will be most effective to work as energy buffer during load transients because of the minimized parasitic inductance.