# How to convert voltage reading to current when using the INAx180 IC?

I am using a INA4180-4181EVM to find a suitable solution for measuring 0-2A of current in a DC circuit. In the datasheet, there is no equation given for calculating the current based on the read output voltage. How can I calculate the current?

Datasheet

EDIT:

The maximum current that should be measured is 2A, the maximum heat dissipation is set to 1/3W. Here are my calculations based on the datasheet: $$R_{shunt} < \frac{PD_{max}}{I^2_{max}}$$ $$R_{shunt} < \frac{\frac{1}{3}W}{2^2A} = 0.0833\Omega$$ Meaning that the shunt resistor must not be larger than 0.0833 Ohms in order to satisfy the power dissipation requirement. To get a starting point for the gain selection, my calculations are as follows: $$I_{max} \cdot R_{shunt} \cdot GAIN < V_{SP}\\ GAIN = \left(\frac{I_{max} \cdot R_{shunt}}{V_{SP}}\right)^{-1}\\ GAIN = \left(\frac{2A \cdot 0.075\Omega}{3.3V}\right)^{-1} = 22$$ Selecting a gain of 20 (and my ADC can read 0-3.3V): $$R_{shunt} = \left(\frac{2A \cdot 20}{3.3V}\right)^{-1} = 0.0825\Omega$$

However, (my understanding is that) by using this value the current is limited to exactly 2A, so it is better to select a value lower than 0.0825 to provide some headroom. I want to test the following values for my shunt resistor to find which one suits my circuit best: 0.070, 0.075 and 0.080.

The current calculation is then done as follows (using Rshunt = 0.08):

float Vshunt = V/20; // Gain reduction, V
float Rshunt = 0.08; // Ohms
float I = Vshunt/Rshunt; // A


Using the EVM board, this seems to match my Fluke multimeter pretty close (have not calculated exact difference yet since I dont have the correct Rshunt value at hand).