Mosfet gate current HELP

[jayzac]

Hi,
I am designing a buck converter using P MOS IRF9540N. However from data sheet, it did not mention minimum gate current to drive this power transistor. Anyone would know how to calculate the minimum gate current required ?

This is the data sheet attached. Thank you .
http://www.irf.com/product-info/datasheets/data/irf9540n.pdf

 

[chuckey]

This is a MOSFET. there is no gate current to speak of, only a leakage of +-.1 uA. You drive it with voltage only, but due to gate capcitance, too high a driving impedance will result in poor risetimes/frequency response.
Frank

 

[darkseid]

Hi

Since the gate of MOSFET is isolated via oxide layer, the gate current is close to zero. But if the switching frequency is high, there will be some switching loses due to the charging and discharging of the gate-oxide capacitance.

darkseid

 

[alexan_e]

It depends on the speed you want, your mosfet has a total gate charge of 97nC,
this is the time it takes for the mosfet to be completely on with low losses (high current and low voltage drop).
nC is time in nano seconds multiplied with the current in amperes.
for example with a gate current of 100mA the gate capacitance will be completely charged in 97nC/0.1A=970ns.
mosfet is a current hungry device while changing stated (turn on and turn off), you need to charge and discharge
the gate capacitance fast to minimize heat and optimize operation of the device and circuit

please read this ww1.microchip.com/downloads/en/AppNotes/00786a.pdf

Alex

 

[jayzac]

What if my gate current is at 100mA, and my buck switching frequency fs=100kHz. Will it too slow for response ?

 

[alexan_e]

I can't tell you what is the correct ratio relationship between the period of the switching frequency and the gate current but you need the mosfet switching time to be as fast as possible.
For 100KHz you have a period of 10us so with a duty of 50% you are changing state every 5us,
from my calculations above, switching on/off takes 970ns using a gate current of 100ma.
So you need about 2us (1us to turn on and 1us to turn off) from the 5us "available" using 100KHz, it seems kind of slow.

Alex