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INA226: Shunt Resistor Selection

Talal Khalil
Prodigy 115 points
Part Number: INA226

Hello, is there criteria/guideline for the shunt resistor selection with the INA226? 

For example, a power supply that supplies a max current of 2.5A, and a 0.001 Ohm shunt resistor results in a 0x10625 calibration value (which exceeds the 16-bit register limit).

Using a 0.005 Ohm shunt resistor resolves the calibration issue. However, I am looking for a more systematic way to select a shunt resistor to use with the INA226.

Thanks in advance.

  • 0
    TI__Expert 7680 points

    Hi Talal,

    There are a couple ways you can think about this. You could determine a shunt resistor by setting 2.5A 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 2.5A and that you want to read positive input voltages.

    So, for case one: 81.92mV/2.5A = 32mΩ (rounded down). With this the lowest current you will be able to measure is Vshunt_LSB/32mΩ = 2.5uV/32mΩ = 78.12uA. 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 5mΩ, then your input dynamic range becomes 12.5mV. The resolution of your current measurements becomes Vshunt_LSB/5mΩ = 500uA. So with this smaller shunt resistor you lose resolution in your current measurements and decrease your signal-to-noise ratio, but you will decrease the power dissipated by the shunt resistor.

    Overall, how you choose the shunt resistor depends on what resolution is desired, how much power can be dissipated in system, and what current noise is present.

    If you are having a hard time deciding what shunt value to use, I recommend looking at our "Getting Started with Digital Power Monitors" app note, found at: https://www.ti.com/lit/an/sboa511a/sboa511a.pdf.

    This document even has a link to a excel design tool that can help you pick the shunt and calculate the calibration register for you.

    We also have a series of videos on Precision labs series: Current sense amplifiers | TI.com that talk about current sensing topics in detail. 

    The video titled: "How to choose a shunt resistor" should be a helpful one.

    Best Regards,

    Angel