LT6105 current range

The IC itself does not set the current range of the sensing, just the amplification of the voltage that is established by the sense resistor. Most users will set the sense resistance to introduce <100mV of voltage drop at max current and set the output resistance so that <1mA produces the full-scale output voltage intended. This will then dictate the gain and the input resistances. Note that there is a tradeoff of gain and output offset error (amplification of the input error) vs heating of the sense resistance, so using the least gain and highest sense resistance that is sensible yields the best accuracy. For 12A, perhaps 0.005 Ohms/1Watt is a good sense resistance, then with a gain of 50 (Rin=100, Rout=4.99k) there would be 3V output for 12A.