I'm using a digital pin on 3.3v pro micro to switch an IRLB3813 mosfet at around 3khz. I'm using it to switch a resistive load up to 30a. I'm searching all over about how to calculate the gate charging current to be switched at around 3khz, but I'm not finding what I'm looking for. May be using wrong search terms.. I'm trying to figure out which gate driver would be a good choice.
Any help is greatly appreciated. I'd like to understand how to calculate this for future reference.
noobdude:
I'm using a digital pin on 3.3v pro micro to switch an IRLB3813 mosfet at around 3khz. I'm using it to switch a resistive load up to 30a. I'm searching all over about how to calculate the gate charging current to be switched at around 3khz, but I'm not finding what I'm looking for. May be using wrong search terms.. I'm trying to figure out which gate driver would be a good choice.
Any help is greatly appreciated. I'd like to understand how to calculate this for future reference.
You choose a current that will switch the device fast enough.
As you haven't said what voltage the load is I'll guess and show a back-of-the-envelope
calculation:
30A @20V.
The MOSFET is 2mOhm so you are already dissipating IxIxR = 1.8W when
on, so lets keep the switching losses down to 1W or less (arbitrary reasonable
choice).
During switching the dissipation goes up to a maximum of 1/4 V I = 30 x 20 / 4 = 150W.
We switch 6000 times a second, so for 1W dissipation keep the switching time down
to 1/150s, or 1/150/6000s per switching transition = 1.1us (this is a conservative
estimate).
Total charge on gate = 57nC, want to switch in 1.1us or faster, therefore I = Q/t =
57n/1.1u = 50mA. Note this for 5V Vgs.
This is within the capabilities of nearly all MOSFET drivers, so just chose a
low-side MOSFET driver that works at 5V supply (not all do).
