How many Amps going over a sense resistor?
you all know the resistors rated 200 to 50 mOhm where we ad more to gain amps…
All the amps.
If you want to sense a 3A driver, you will get all 3A through the sense resistor.
The circuit is sensing the voltage across the sense resistor. I.e. a 1A driver with a 200mOhm sense resistor will look for 1*0.200 -> 0.2 volt across the resistor. If you want 1.5A you want a 0.2/1.5 -> 0.133 ohm -> 133mOhm resistor.
Calculating with parallel resistors: 1/(1/0.133-1/0.200) -> 0.397 it shows that a 397mOhm parallel with the 200mOhm is 133mOhm, i.e. soldering a 397mOhm on top of the 200mOhm sense resistor will give the wanted increase.
Of course, you cannot get that value and will have to round up/down to an existing value.
Because soldering and circuit board traces add a few mOhms, the calculations will not always match perfectly.
With a buck converter it would depend on where the sense resistor is located in reference to the switches (diode and mosfet). It might see the same current as the load or it could be far less, but at a much higher voltage.