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I think DrAzzy is doing a good job of explaining how to read the data sheet. And there is also lots of good detailed information if you google "how to read MOSFET data sheet". if we just look at this particular MOSFET that I mentioned (ZXMN2F30FH), I can show how I go about finding out how much current it can handle:
first, find out how much power dissipation it can handle. to do this, I have to decide how hot I want to run the transistor. I usually set +125C as maximum. then I decide on the hottest ambient temperature. let us say +40C. 125-40=85C. then I find the figure for thermal resistance from junction to ambient, 131K/W. so the maximum power dissipation it can handle is 40/131=0.3W. then I estimate the resistance Rds(on) at 3.3V. for this transistor I have values for 2.5V and 4.5V, and I decide that the resistance at 3.3V will probably be close to the average of these two values, so I say that at room temp and 3.3V gate voltage the resistance is (0.065+0.045)/2=0.055 ohm. but at 125C the resistance will be higher. Fig 4 tells me that it is about 1.3 times higher at 125C than at 25C, so I will use 0.072 ohm for the resistance value. Now that I know R and P it is possible to calculate the maximum current I that the transistor can handle. it is sqrt(P/R) or 2.0A.this is the procedure that I normally use for quickly figuring out how much steady state load current I can safely run through a specific MOSFET.
2A is a lot less than 4.9A, is it not?
if the MOSFET is switching on and off there will be additional power loss especially is it is driven from a GPIO pin, so it may be necessary to use a gate driver between the GPIO pin and the MOSFET gate - especially if the MOSFET is larger than this SOT23 size device we have been discussing.
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tage
So, I just want to be sure that I'm understanding this correctly since when I look at the datasheet, it says the transistor you linked to can handle a continuous current of 4.9A at 4.5V on the gate which is definitely a lot more than 10W... am I reading this and understanding you correctly?