Hello,
Let's take a P-Channel MOSFET SI2323DS which is in SOT-23 package. The datasheet states it has 4.7A Id continious and Rdson 0.039 Ohm. I would like to use this transistor to switch 1A load. I know the Rdson is low enough, but the SOT-23 pins are so small that I'm not sure that they can handle such load. So, has anyone ever seen a mosfet in SOT-23 drive such high loads?
4.7A is not DC current, it is pulsed signal (please refer to Note a, at page 2 of datasheet).You have to ensure the power dissipation should not exceed absolute maximum value and result in junction temperature is higher also than 150°C. Unless you dont pass these values, it should be OK.
For the help of calculation of thermal management, you can also utilize thermal model given. It should help.
Well, if the thermal consideration is the only thing I should worry about:
P=1A^2 * 0.039 Ohm = 39mW
...giving me 40mW conduction losses (there are practically no switching losses in my application). So, that puts me well withing the standard 300mW allowable power dissipation for SOT-23. I still find it difficult to believe you can put 1A through such a small package :?
You can, and I have. Just be careful with the PCB traces coming into the part - make sure they're thick enough to handle your current without excessive resistance.