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INA226: VBUS Reverse Polarity Protection

Part Number: INA226

I am using an INA226 in a low side sensing application. The bus working voltage could be up to 120V with an absolute max of 125V. I am looking at using a 150k/68k voltage divider to work with the internal 830k pulldown and drop the voltage to 36V. I am ok with using a crowbar circuit to blow a fuse on an overvoltage condition. However I would like the device to recover from reverse polarity without any fuses blowing.

Would the high input impedance of the voltage divider protect the chip from -120V (-36V on pin, although maybe there is an internal clamp)? Or do you have any other suggestions for how best to protect the chip without any loss in accuracy? I will be calibrating the devices so I only care about relative accuracy. But I would prefer to have a high gain accuracy and low tempco.

  • Hi Michael,

    Thank you for your question. An engineer from our team will reply tomorrow during normal work hours.

    Best regards,

    Ian Williams
    Applications Manager
    Current & Magnetic Sensing
  • Hello Michael,

    For reverse polarity, perhaps you could use a p-channel mosfet, Zener diode, and resistor such as below. In this instance when you have 36V at the divider node, the gate to source voltage should be <-4V allowing current to flow through the drain to source channel and provide a voltage around 36V to the INA226 bus pin. In the instance your bus voltage reverses polarity, the gate voltage rises above drain and source and results in the mosfet channel closing , thereby creating an equivalent open circuit yielding a bus voltage that should be less negative than -0.3V. The purpose of the Zener diode would be to ensure the mosfet Vgs specification is not exceeded while the resistor helps limit the current needed to generate the desired Vgs voltage.

    As for the divider values you chose, I think those typically will be sufficient for limiting the voltage on the bus.  However, for the purpose of calibration or post-processing I just would like to alert you that there may be some variation (up to 15%) with the input impedance of the INA226.  Therefore you can expect the following variation   The top corresponds to the typical, while the bottom two correspond to the divided voltage you might see with the max variation with your max 125V condition.  In this instance, you do risk running in the nonlinear region of operation in which the bus exceeds 36V.  However, the device will survive this as the bus is rated for 40V max.