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INA3221 minimum voltage measured

WhiteHorse
Genius 4430 points

Other Parts Discussed in Thread: INA3221

E2e,

I am looking at the INA3221 and was wondering what the minimum voltage is that can be measured for the shunt voltage? I believe this is indicated by the LSB value for the shunt voltage, which is 40uV. So as I understand this, the INA will measure the shunt voltage in steps of 40uV. Therefore, the smallest value I can measure is also 40uV. I am trying to figure out what value of sense resistor I should use, and want to make sure that I do not pick a value that is too small to be registered at the minimum current.

 

For example, a value of 80mA and a .0005Ohm sense resistor would be the minimum possible current that I could measure (resulting in 40uV). Since it is a 13 bit ADC this results in 8192 steps (2^13), half of which are positive and half are negative (indicated in the -163.8mV to 163.8mV range).

 

Thanks for your help.

 

Regards,

WH 

  • 0
    TI__Genius 15770 points
    Hi WhiteHorse,

    I will be reviewing your question and get back to you.

    Regards
  • 0
    TI__Genius 15770 points
    Hi WhiteHorse,

    Yes, as you mentioned the 40uV is step size is the minimum voltage you could read. Although, the VOS of the device is typical 40uV, max 80uV...so you might need to calibrate this offset if you want to read at that very small voltage level.

    When you are trying to calculate the optimal shunt resistor value you use your maximum expected current as reference. You can watch Series 4 of our training videos. This video will guides you in the selection of shunt resistor size.

    e2e.ti.com/.../467332

    Hope this helps!