• Resolved

INA122: Incorrect Output Voltage

Intellectual 330 points

Replies: 2

Views: 21

Part Number: INA122

I am testing the circuit below. The 100Ohm shunt is used to measure current and the 36kOhm simulates a 100uA load. However the output is always around 2.7V instead of the expected 1V output.

What could the issue be?

  • Hi Luke,

    Thank you for your post. I can help you. 

    On a 5V supply, the input common mode voltage range on the INA122 is 0 to 3.4V. This is shown on page 2 of the datasheet, please see the image below.

    Your 3.6V excitation is beyond this range. I would recommend reducing this 3.6V to a value within the input common mode voltage range of the INA122. I chose 1.7V. Please see the image of the new schematic below. I also attached my simulation file for your reference:

    INA122 new schematic TINA.TSC

    -Tamara Alani
    Learn more about IAs here.

  • In reply to Tamara M Alani:

    Hi Tamara,

    thank you for your reply.

    Unfortunately I missed out on that. Just to clarify, if operated with a dual supply rail, the common mode is still 0V to 3.6V?

    We cannot change the 3.6V since it is the voltage supply required for our load. Instead we are considering using the INA138 now which has a common mode voltage of 60V and thus it seems to be more appropriate for our application. Can you let me know what you think about this please?

    Thanks and regards
    Luke