• State TI Thinks Resolved
  • Locked Locked
  • Replies 2 replies
  • Answers 1 answer
  • Subscribers 48 subscribers
  • Views 915 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

INA117: 200V common mode

Jonathan Geronga
Expert 7930 points
Part Number: INA117

Hi Team,

Our customer would like to ask how does the 200V common mode with 15V rails decrease with resistors on the inputs in the circuit below:

Please let me know if you have any questions with the customer.

Thanks,

Jonathan

  • 0
    Guru 140200 points

    Hi Jonathan,

    it's not recommended to add such high resistances to the inputs of INA117 as this will totally ruin its brilliant common mode rejection. Please read the datasheet:

    Kai

  • 0
    TI__Prodigy 715 points

    As Kai said, these large external resistors will completely kill the performance of the INA117.  So much so that you'd likely be better off just building a discrete diff amp with your 1% resistors.  Check out our new INA TI Precision Labs videos to help guide you on the diff amp.    

    You're not really using the INA117 in a way it shines anyhow.  A high common mode diff amp is intended to measure relatively small voltages stacked on top of high common mode voltages.  Here it appears you are measuring a bus voltage relative to ground.

    If you were to use the INA117 for its high CMR performance (no resistors at input), check out this app note for guidance as how to widen its differential range.