INA226: Shunt resistor value selection fo INA226

Hey John,

There are a couple ways you can think about this. You could determine a shunt resistor by setting 3A to correlate with the maximum possible input voltage allowed by the INA226, which is +-81.92mV. Let us assume you are measuring unidirectional current, so current will go from 0A to 3A and that you want to read positive input voltages.

So for case one: 81.92mV/3A = 27mΩ (rounded down). With this the lowest current you will be able to measure is Vshunt_LSB/27mΩ = 2.5uV/27mΩ = 92.59uA. Of course this is not considering differential input noise in the current. If the noise is making your measurements vary by a few LSBs, then measuring one LSB will be harder and may require averaging and longer ADC conversion times.

If you choose 6mΩ, then your input dynamic range becomes 18mV. The resolution of your current measurements becomes Vshunt_LSB/6mΩ = 416uA. So with this smaller shunt resistor you lose resolution in your current measurements and decrease your singal-to-noise ratio, but you will decrease the power dissapated by the shunt resistor.

Overall, how you choose the shunt resistor depends on what resolution is desired, how much power can be dissapated in system, and what current noise is present. You can always refer to our training videos here: training.ti.com/getting-started-current-sense-amplifiers-session-15-programming-power-settings

Sincerely,
Peter Iliya
Current Sensing Applications