I've been looking for MOSFETs to build a couple h-bridges for stepper motors (rated at 0.3A), and I'm really surprised at how tiny of a MOSFET I need to drive this motor. For the p-channel MOSFETs I'm looking at these http://www.irf.com/product-info/datasheets/data/irlml2246pbf.pdf After doing some calculations it looks like I'll get about 80m-ohms drain to source with -12v gate to source at 70 degrees C. So I should be able to push the recommended max of 2.1A through it all day without heatsinking.
Is this all correct or am I missing something? I just can't believe that this tiny thing can handle 2.1A all day long. I know for a fact that I'm leaving out switching losses, but I honestly have no idea how to calculate that. I also don't imagine it'll have a big effect when I have such a big overhead.
EDIT: A question about flyback diodes. I know it's generally recommended to include separate ones and I usually do, but what's the theory behind this? It seems to me like the internal diode in the MOSFET should be able to handle the back EMF. Maybe someone more knowledgeable than me will be able to make something of the winding inductance in relation to back EMF voltage, so here's the motor product page: https://www.sparkfun.com/products/9238