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INA213: Inquiry Regarding INA213 Gain Calculation

kim kwangsu
Prodigy 40 points
Part Number: INA213
Other Parts Discussed in Thread: INA791, LMP8646, LMP8645

Tool/software:

Dear TI Engineer,

I hope this email finds you well. I am a circuit design engineer working with the INA213, and I have a few questions regarding this chip.

I am attempting to achieve a gain of 7.14x by placing 120kOhm resistors in series with the V+ and V- inputs, with a sensor attached between them. Theoretically, this approach seems correct. However, when I run a simulation using TI tools, the gain does not reach 7.14x, and even after conducting real-world experiments, the observed gain seems to be close to 1x.

Could you please help me understand why this is happening and whether this circuit design is incorrect?

Thank you for your time and assistance. I look forward to your response.

KWANSU KIM
Senior Engineer

  • 0
    TI__Expert 8455 points

    Hello Kwansu,

    I don't think this will work. The voltage drop across the 120kΩ resistors will be the same on both inputs because the input bias current is the same on both pins, so the Vsense voltage will remain unchanged in the ideal case.

    The input bias current also changes based on the common-mode voltage and the reference voltage, as shown in the datasheet plots:

    Finally, the input bias current only averages to this value, the actual input bias current could have AC componets that would need to be averaged out.

    We do have parts with adjustable gain however, the INA790, INA791, and INA750 all support adjusting the gain via an external gain network.

    The LMP8645 and LMP8646 also support adjusting the gain using an external resistor.

    Let me know if you have any more questions on this,

    Levi DV