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INA240: Gain Error at Very Low Sense Voltage

Ryan.Bishop
Expert 3900 points
Part Number: INA240
Other Parts Discussed in Thread: INA190

Hello,

I'm looking for a current sense amplifier that has very good linearity and gain error at low sense voltage (<10mV). I've found devices like the INA240 and LMP8480, but noticed that they don’t spec the gain error below 10mV sense voltage, or aren’t clear on the range for which the gain error spec is valid, respectively.

Could you help me narrow down which of the available devices will have the best linearity for applications with low sense voltages? We need a gain around 50V/V and common-mode range is never more than 55V.

Is there any test data for these low sense voltages?

Regards,
Ryan B.

  • 0
    TI__Genius 17100 points

    Hi Ryan,

    Current sense amplifiers have two main sources of error: offset and gain. Offset error is fixed based on the input offset voltage while gain error is a fixed percentage across the sense voltage range.

    At low frequencies, offset error dominates the total error. For accurate measurements in the low Vsense range, low offset voltage is critical. The INA240 has a typical 5uV and max 25uV offset, the lowest offset spec in our catalog, so sensing voltages at 10mV will have 0.05% - 0.25% error which increases as Vsense decreases.

    Production data for the INA240’s offset can be found in the datasheet and is shown below:

    Also included in the datasheet are equations for noise calculations as shown:

  • 0 in reply to Manuel Chavez
    TI__Expert 3900 points

    Hi Manuel,

    Thank you very much for that information.

    Luckily, the customer is okay compensating for the offset error of the current sense amp in their measurement.

    Ultimately, what we are looking for is a predictable amount of gain error and linearity when the sense voltage is small.  The errors don’t have to be infinitesimally small.

    1. Do we have any data for the INA240 at sense voltages < 10mV?
    2. Given that offset isn't the biggest concern for the customer, do we still recommend INA240 for linearity at low sense voltages?

    Thank you!
    Ryan B.

  • 0 in reply to Ryan.Bishop
    TI__Genius 17100 points

    Hi Ryan,

    There isn’t accuracy data for the device beside what is included in the datasheet, but device error will converge to the offset error at sense voltages below 10mV. A low tolerance shunt resistor will help keep measurements accurate.

    Given the max 55Vcm spec, the INA240 is certainly the appropriate device here. If your customer’s Vcm range were 40V max, the INA190 has competitive performance.


    Regards,
    Manuel Chavez