What happen if we choose bootstrap capacitor value too high in high side gate driver applications? Can it be harmful for MOSFET/IGBT or it is just not important?
The only drawbacks which came into my mind:
- it takes longer to charge it up after startup
- You need a capacitor with low ESR if you need to utilize the whole voltage for the switch drive. The ESR will have a voltage drop in it during charging up the high-side gate, plus it slows down the process. You need a cap where it will not be the bottleneck in your design.
- a large cap has lower self resonance frequency. You want that your capacitor behaves as a capacitor at the switching frequency and its first few harmonics.
- more expensive
Increasing the bootstrap cap well beyond the gate cap - it might be better to think in sum of charges, but saying cap is easier - will not give you much. As long as the voltage after the charge sharing process is close enough to the supply you will gain nothing from a bigger cap.