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INA214: Gain drops under high frequency common mode noise

Shenhua Zhang
Prodigy 640 points

Part Number: INA214
Other Parts Discussed in Thread: INA240

Hi,

Thanks you for your time!

My customer is using INA214 with shunt resistor to measure the output current of their power converter. They found the gain of INA214 abnormal under some case, shown as below.

The Y-axis represents the output of INA214, the X-axis represent the current through shunt resistor, which is proportional to the input voltage of INA214. So that the slope of the curve represents the gain of INA214.

There are three different curves of three colors, meaning three different input voltage working conditions(40V, 54V, 60V), but output voltage and current are totally the same. The only difference of the three colors, blue, orange and gray represent different switching frequency of the power converter. And blue and orange ones are the same, 1MHz, but the gray one is higher, 1.4MHz. The higher frequency only will bring different frequency of common mode noise.

So I wonder if different frequency of common mode noise will affect the gain of INA214?

  • 0
    TI__Mastermind 34570 points

    Hello Shenhua,

    Thanks for using the forum.

    Yes the Common-Mode Rejection does change with frequency.  Depending on the differential voltage frequency changes and parasitic you could see the gain change as well.  The two plots below from the data sheet could be the reason you are seeing the issues at 1.4MHz.  A reason is the CM is not getting rejected and feed through from the input to the output.  You could look into the INA240 has better CM response.

  • 0 in reply to Javier Contreras4
    TI__Prodigy 640 points

    Hi Javier Contreras,

    What I am still confused about is that, why poor Common-Mode Rejection could affect the DC gain performance?

  • 0 in reply to Shenhua Zhang
    TI__Mastermind 34570 points

    Hello Shenhua,

    Once a common mode signal is applied and it does get to the output it can have a non-symmetrical effect and create a DC offset.  Or the signal gets rectified and creates a DC signal at the output.  Most amplifiers have issues with high speed common mode changes.  Also if the CM change is large enough and couples through to the output you could have issues as the output could clip creating a non symmetric output which would create a DC offset as well.

    To narrow this down you can set a scope shot of the input and output to determine if either of the issues I mentioned are the reason for the issues.

    Most current sense amplifiers have issues with fast common mode spikes the INA240 has a method internally to help deal with this.

  • 0 in reply to Javier Contreras4
    TI__Mastermind 36620 points

    Hi Shenhua,

    We haven’t heard back from you for a while, and assume your issue has been resolved. If not, please post back and we’ll continue to support you.

    Regards, Guang