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INA317: INA317 used for low side current sense amplifier

Vasu Poojary
Intellectual 390 points
Part Number: INA317
Other Parts Discussed in Thread: LM7705, INA190, INA191

Hello E2E Expert,

We are looking for INA317 application to be used for low side current sense amplifier  (microvolts drop across the low side shunt to be amplified  )

One side of shunt will be referenced as system ground and drop across shunt needs to be amplified as differential input to INA317.

But from datasheet of INA317  section "8.2.2.9 Single-Supply Operation"  it is mentioned that

"With single-supply operation, VIN+ and VIN– must be 0.1 V more than ground for linear operation. For instance, the inverting input cannot connect to ground to measure a voltage that is connected to the noninverting input "

Which is conflicting with our application .

Can you please confirm whether INA317 can not be used for low side current sense amplifier ?

Reason we are going for INA317 is offset voltage is in the range of microvolts and operating current is in the range 50uA.   Our application requires very low operating current.

Please suggest any other suitable low operating current and low offset  current sense amplifier

Thanks

Regards

Vasu

  • 0
    TI__Genius 10305 points

    Hi Vasu,

    Thank you for your interest in INA317. Unfortunately this device does have an input common-mode limitation 100mV above the negative supply. If a negative supply is available, the INA317 can be used for low-side current shunt but this is not possible with a single supply due to the input limitation.

    There are current-sense amplifiers that are designed specifically for low-side current monitoring on a single supply. The INA191 has very low offset, low quiescent current, enable function, and an input range that can go 200mV below ground. This device is covered by the current sense team so I will loop them in for their input, they may have other device recommendations as well.

    Regards,

    Zach

  • 0
    Guru 140200 points

    Hi Vasu,

    if you want to use the INA317, I would add a negative supply voltage. A simple and tiny DC-DC-converter with pi-filters at the input and outpus could do the job, eventually in combination with additional voltage regulators.

    Even with the LM7705 the circuit can be made to run:

    Of course, add sufficient filtering arround the LM7705:

    7725.lm7705_konkret.pdf

    Kai

  • 0 in reply to kai klaas69
    TI__Expert 4720 points

    Hello,

    Kai is correct using a negative negative supply (less than -0.1) will allow for you to use the INA317. 

    If you cannot do this as Zach pointed out you can use one of TI's current sensors. If your shunt drop is in the uV range then calibration will be necessary as most of our INA current sensors have uV offset voltage. You mentioned uV shunt drop but did not include the shunt or current to be measured values.

    I would suggest using the INA190 or INA191 as they have comparable quiescent current to the INA317.

    This can also be done with a discrete op amp (input rail to rail for single supply) similar to the picture below. The gain setting resistors will cause gain error if not carefully selected. (Picture just for reference resistors must be chosen for the application.)

    Regards,

    Cas