If I have a setup where a N MOSFET drives a heavy inductive load (say, 25A peak), can I use the MOSFET's internal resistance to measure said current the same way I would use a shunt resistor?
The value of the equivalent series resistance when the MOSFET is active (i.e. Rds-on) is usually very low and easy to find in the MOSFET's datasheet. I know it is not ideal, and will strongly depend on the FET's temperature a well as the current (so I have a loop there). Still, is there any serious impediment to this approach?
The reason I want to do this is because I have a system where I need to minimize component count as well as avoid any extra losses (i.e. shunts) when driving the inductive load, but can compute some corrections/linearization on a temperature-sensing micro-controller if needed.
I am almost 100% I saw a LiPo battery manager that appeared to do something similar, but I am unable to find it. As I recall, this IC estimated the charging current using something similar to what I just described. But maybe I am just mistaken.