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INA282-Q1 Input Filter

Toshio Ushikubo
Mastermind 9620 points
Other Parts Discussed in Thread: INA282-Q1, INA210-Q1

Hello,

 

Customer is considering to use INA282-Q1.

Please answer following question from customer.

 

INA282-Q1 datasheet page 14 has following explanation.

 

“Despite the use of internal zener-type electrostatic discharge (ESD) protection, the INA28x-Q1 does not lend itself to using external resistors in series with the inputs without degrading gain accuracy.”

 

But datasheet has no explanation about relationship between input series resistor and degradation of accuracy.

 

Please explain the relationship between input series resistor and degradation of accuracy, and equation like

INA210-Q1 datasheet has.

 

Best Regards.

  • 0
    TI__Mastermind 20580 points
    Hi Ushikubo-san, the appropriate applications engineer has been assigned to this post. Scott
  • 0 in reply to Scott Monroe
    TI__Mastermind 20580 points

    Hi Ushikubo-san,

    I've learned this device is now supported by a different team.  I'm moving the thread to their forum and hopefully they can help.

    Scott

  • 0 in reply to Scott Monroe
    TI__Mastermind 18780 points
    Dear Ushikubo-san,

    Unfortunately we do not always characterize gain error factor for all of our parts. We do not have the formula you are seeking for the INA282-Q1. We only stipulate that it is not recommended to place resistors in the input path, as they will affect the gain error of the part, but do not quantify this error. You would need to characterize this error if you wanted to place resistors in this way.

    Carolus
  • 0 in reply to Carolus Andrews
    Mastermind 9620 points

    Hello Carolus-san,

     

    Thank you for your answer.

     

    Please answer additional question from customer.

     

    INA282-Q1 datasheet explains the total error calculation (page 19).

    It uses Vos value at 25C.

    If customer needs total error from -40C to 85C, should we add temperature drift of 187.5uV max(1.5uV max x (40C+85C)) to Vos max?

     

    Best Regards.

  • 0 in reply to Toshio Ushikubo
    TI__Mastermind 18780 points

    Dear Toshio,

    Not quite. While you are on the right path in that the drift spec is applied to the temp change, dont forget that the offset will swing on either side of room temperature, so what you've technically calculated there is a non-symmetric peak to peak value. Drift is typically calculated at a specific value of temperature, i.e. a known operating point from the customer. Does your customer have a desired operating point that they wih to operate in? If you can find out that value, then you use the drift specification to shift the offset to that point. If they want worst case values, you need to piecewise it in 2 separate directions from room temperature, such that moving up from room temperature you achieve a worst case offset of 85C-25C added to Vos, and moving down from room temperature you achieve a worst case of 25C+40C deducted from Vos. Let me know if I need to clarify this further.

    Carolus