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INA226: Why is VBus connected before the sense resistor?

Mark Nohr
Intellectual 570 points

Part Number: INA226

While the power calculations and examples don't list the drop across the sense resistor as a factor in calculating power I'm wondering if it actually is considered. Otherwise using the pre-sense_resistor voltage seems to introduce an unnecessary error.

What am I missing here?

  • 0
    TI__Mastermind 32395 points
    Hey Mark,

    Thanks for posting to the forum. The VBUS pin will measure whatever voltage node it is connected to. The INA226 will then multiply this voltage with the calculated current to get power value. If the VBUS pin is placed on the high-side (more positive in voltage) of the sense resistor, then the power dissapated across the shunt/sense resistor will be included in the power calculation. If VBUS pin is connected to the more negative voltage side of sense resistor, then power across sense resistor will not be in the final power calculation.

    Where the VBUS pin is connected is dependent upon what your system mandates. In the datasheet we show the VBUS pin connected before (more positive side) the sense resistor as an example. This is certainly not the only way the circuit can be configured.

    Please let us know if you have more questions.

    Best,
    Peter Iliya
    Current Sensing Applications
  • 0 in reply to Peter Iliya
    Intellectual 570 points

    Ok. Thanks Peter.