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INA181: Gain setting

Dice-K
Mastermind 7470 points
Part Number: INA181
Other Parts Discussed in Thread: INA138, INA139,

Hello.

Can I add an input resistance to the INA181A1 and set the gain to "10"?

By Page-25 of SBOS793D.
When RF is added to the input, the gain shifts.

Gain = 20 = R2/R1

R1=25kΩ
R2=500kΩ

R1 is the input side of internal resistance.
R2 is the output side of internal resistance.

When RF=25 kΩ is added to the IC input side,  will the gain be "10"?

R1=25kΩ+25kΩ=50kΩ
R2=500kΩ
Gain = R2/R1=10

Regards,
Dice-K

  • 0
    Guru 140200 points
    Hi,

    the INA series shows extremely good CMRR. This is achieved by having the feedback resistances of input stage on the same die and by using a very precise manufacturing technique. When adding resistors to the inputs the high internal symmetry will be destroyed by the manufacturing tolernaces and long term drifts of these resistors. That's why only resistor values up to 10R are allowed at the inputs.

    Kai
  • 0
    TI__Genius 17100 points
    Hi Dice-K,


    The INAx181Ax devices all have an internally matched fixed gain. Because of this design, an external resistor network cannot be used to predictably program gain.

    These internal resistors (R1 and R2) are trimmed to result in an accurate 20V/V gain, but their exact values may vary by 20%. Adding a 25kΩ resistor to the varying internal resistor network will affect the input offset voltage and change gain within ±10% not including the external resistor’s tolerance.

    The A1 version of the INA181 will have a fixed gain of 20V/V, but if you are looking for programmable gain devices to achieve 10V/V, our current-output INA138 and INA139 might work for your application.



    Thank you for choosing TI products,
    Manuel Chavez