When You Assume....
Back in the start of my Alarm interface project, I ran into problems with my current limiting circuit. My little 3A FET would go up in smoke with limited to 500mA and I just put this down to a need to heatsink the FET. The thinking here is that passing 500mA when switched on was too much for the little SOT23 package.
I was wrong!
But before I knew that, I decided to beef up my circuit, switching the PMV48XP for a TD2955PT4G which comes in a D-PAK package, and rated to run with a Heavy Duty 12A steady state current. 500mA should be nothing for this beast, and the bigger case might compensate for the lack of heatsink (I was trying to get a physically small solution).
However, the only thing I knew was that I was going on guesswork here. I didn't have any hard maths that proved what I was thinking was correct, and rather than commit to winging it on my next run of Seeed studio PCB's I built a test circuit to check it out.
Rather glad I did that now!
High Side Limit Schematic
High Side Limit PCB