1. If I connect 2 or 3 mosfets in parallel, the gate capacitance will just add up. Right?

2.I have an condition where:

• From Vgs vs Qg graph I have noted total gate charge Qg. Which in my case is 22nC.(FDS6690A)
• Now according to formula Ig= Qg/Ttransition.
• In my application Ttransition of 3-10ms is sufficient.
• So by equation Ig= 22nc/5ms = 4.4uAdc.
• If I use a push pull opamp, which can go between rails i.e 10V or 0V.
• How to select gate resistance in this case?

 

Post the complete schematic for your circuit.

 

Yes, the capacitance of the gates simply adds together.

Selecting the resistor is mostly about isolating the inductance of the wiring (or circuit board traces) because the high speed switching that is proper for MOSFETs causes inductive ringing. The resistor is not intentionally used to slow down the charging time of the gate capacitance. You might use resistance to keep the op-amp from exceeding its current delivering ability.

Does that help?

 

I always use 5-20 Ohms never had any problems.