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LM43602-Q1: Output Capacitor Selection

Masatoshi Oguri
Expert 4780 points
Part Number: LM43602-Q1

Hello,

Would you let me know how the equality 19 and 20 in the datasheet shown below were derived?

Or make a brief explanation about what is compared to what in these inequalities?

One of my customers is making a lot of trouble to understand it.

Thank you.

Oguri (TIJ automotive FAE)

  • 0
    TI__Mastermind 18940 points
    Hello Masatoshi-san,

    I moved this post to the SIMPLE SWITCHER forum and will forward the question to the applications engineer for this device.

    Regards,
    Denislav
  • 0 in reply to Denislav Petkov
    TI__Genius 15810 points

    Hello,

    One of the purpose of the output capacitor is to hold up the output voltage when there is the load experiences a surge. Customers will have different specs on what the max droop they wan to allow. The capacitor needs to be sized according to that. The components of the equation are 

    r = ripple ratio.
    deltaVOUT = allowed droop

    What the equation says is that if you choose a capacitor value higher than calculated, you should be able to obtain the load surge response you wanted. This doesn't completely factor in the internal loop compensation. I have attached a presentation that details the calculation.

    Capacitors Calculation for DC-DC Converters.pptm