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need help for Bootstrap component (capacitor and diode) selection.

ASHISH KUMAR RAI92479
Prodigy 40 points
Other Parts Discussed in Thread: SM74104

Hi .

I am using MFET gate driver SM74104 (national part). Please  general guidelines to choose the value and rating for Bootstrap capacitor. Bootstrap diode is an option, provided with IC. Do we have thumb rule or is it IC specific? PWM frequency is 100 Khz in my case.

  • 0
    TI__Mastermind 22756 points

    hi

    the rule is Cboot = 10 x Cgs of the HS FET you are going to drive...

    normally higher the Cboot better the performance but there is a drawback as well:

    indeed, at start-up, this cap is empty and then bigger the cap bigger the current inrush across the diode...

    normally a 2-3Ohm resistor is put in series to the diode as current limiter...

    this cap has to exhibit good behavior Vs temperature, so a X7R is reccomanded...

    normally, Cboot spreads in the 10-220nF range...

    Vincenzo