In order to calculate capacitance of bootstrap capacitor, I searched around and found two different formula from Ti and Infineon. The Ti version states: Ti Application note

while Infineon version say: Infineon Application note

I think the basic idea behind these two formulas are same: dividing maximum charge may loss when high side MOS conducting, by minimum change of voltage. But I failed to figure it out on myself that why \$Q_g\$ was multiplied by \$2\$ in Infineon's version and again the whole numerator was doubled.

So far the Ti version makes more sense for me as \$Q_g\$ itself is the charge we loss in a switching cycle and also OnSemi seems to give similar formula (pg 5). But I believe there is some reason why Infineon engineers write this formula. I am currently studying how to design half bridge driver and I have selected IR2103 from Infineon. And that's why I want to ask which formula should be used and why?

  • \$\begingroup\$ I just thought it was a fudge factor. \$\endgroup\$
    – DKNguyen
    Jul 21, 2019 at 4:55
  • \$\begingroup\$ the germans have te ability to complicate even very simple things. \$\endgroup\$ Jul 21, 2019 at 5:52


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