Please check the datasheet of the opamp TSZ124, which does the current measurement at the X-NUCLEO-IKA01A1. On page 26 of the datasheet of that opamp you will find some calculations for such a current measurement (it does not matter that it is a low-side measurement). Equation 5 explains the influence of the offset voltage: the IKA01A1 uses factor 12k/100+1=121 times 8µV (max) = 968µV. This is the reason for the current limit of 100mA via Rs=20mOhms, giving 2mV voltage drop.
The ratio between the smallest shunt voltage and that factor (multiplied offset voltage) would have a negative impact to the accuracy if you would lower the shunt resistance.
On the other hand: if you need the opposite, i.e. a higher minimum current, you could easily increase the shunt resistance Rs. 😁
Good luck!
/Peter
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