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INA181: Providing reference with voltage divider

Logan Rosenmayer
Prodigy 10 points
Part Number: INA181
Other Parts Discussed in Thread: INA240

My question pertains to the need for a low impedance reference for the INA181.  In the INA240 the block diagram shows a simple voltage divider feeding a reference for the zero input level for the amplifier, can this be done for the INA181 as well or is a buffer amplifier a must as in figure 45 of the datasheet(INA181).  My application is low-side current sense for FOC.

  • 0
    TI__Mastermind 32395 points

    Hello Logan,

    Yes. This same resistor-divider technique can be used to provide the reference voltage to the INA181. However, this will add some gain error to the device as the effective parallel resistance is now added onto the internal feedback resistor of the INA181. When doing this it is best to keep the resistor values as low as your power budget will allow to minimize this gain error.

    When doing this technique, you can minimize error by having the ADC read the differential output voltage of INA181: VOUT-to-VREF and performing a two point calibration to determine the real gain of the circuit. Consider watching this video to learn more about gain error and calibration for these devices: 

    https://training.ti.com/ti-precision-labs-current-sense-amplifiers-gain-error

    Sincerely,

    Peter

  • 0
    Guru 140200 points

    Hi Logan,

    but keep in mind that a resistor divider without buffer can degrade the common mode rejection ratio. This might be of marginal effect for a low side application but not for a high side application.

    Kai