I try to switch a 12V non-inductive load drawing 400-500mA with a IRF3708 Logic-Level-MOSFET with the 5V from an Arduino. I am new to MOSFETs but I simply cannot find my mistake. I think I fried some MOSFETs using the 5V because Rds(on) was too high (3-4Ohm) and this resulting in too much heat which killed the MOSFETs. I hope this conclusion is correct. But the datasheet states that at 4.5V Ugs Rds(on) should be in a 9.5-13.5mOhm range. Even if it may be optimistic I don't get why it is in the Ohm range and not even near the values in the datasheet.
What am I understanding wrong here?
With a load of 1k my Amperemeter gives me a current of 11.8mA @12V with 5V applied to the gate. This equals a series resistance of 1.0166kOhm. This results in a Rds(on) of 1.66Ohm. Ok it is lower than my wrong measuring but still a lot higher as in the datasheet. If 500mA would flow like in my application this Rds(on) gives an UDS of 0.664V which result in 265.6mW of heat at the MOSFET. Correct?