how to calculate boot capacitor value in step down converter

[Julia2013]

Hi all:

I am using TPS5430 (a 3-A, wide input range, step-down SWIFT™ converter)

for the capacitor between pin 1(BOOT) and pin8 (PH) ,
it tells me to use 0.01uF in the datasheet.

But, Why 0.01uF?
How is it calculated?

I am very curious.
Can any one give me some hint on the rules to follw during calculation?

Thanks a lot in advance

 

[FvM]

The required capacitor value depends on switching frequency, maximal duty cycle, static gate driver current consumption (if any), total gate charge, minimal projected Vgs,on. Many of these parameters are internal to the chip and unknown. So you can't calculate it.

Why do you worry about bootstrap capacitor value and don't question any other component specification in the datasheet? How can you be sure that the chip is working at all? :smile: