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INA211, How to measure the current by low side (GND)?

Aska Lee
Intellectual 610 points
Other Parts Discussed in Thread: INA211

Hi

In INA21x datasheet, we can know how to measure the current by high side (Output voltage). It is ok for that.

But we have new request. The output voltage is high voltage (around 440Vdc). So I tried to use INA211 to measure the current by low side (Gnd).

But I still got some error. I am not sure the current schematic is ok or not.

Could you please advise the schematic for low side measurment by using INA211? Is there anything I need be careful?

Thanks.

Aska

  • 0
    TI__Mastermind 25825 points

    Hello Aska,

    I have attached a TINA simulation depicting the INA211 in a low-side configuration.  You will want to ensure that you Kelvin-connect the shunt resistor and you may want to include provisions for filtering as shown by the attached simulation.  Additionally you may want to keep in mind that the product of the load current and the shunt resistor will be the ground potential as seen by your system load.  Therefore you'll probably want to keep it as small as possible.  Please let me know if you have any further questions.

    aska.TSC
  • 0 in reply to Pete%20Semig
    TI__Intellectual 2230 points

    Hi, Pete,

    In your simulation file, you made annotation that ‘ Common-mode and differential-mode filtering *Keep C4 and C3 to

    1/10th the value of C2 to preserve CMR*’ , why is that? i don't see the effect of filering capacitor on CMR. Thanks a lot.

     

  • 0 in reply to Nicole Han
    TI__Mastermind 25825 points

    Hello Nicole,

    Please refer to the following application note. Please pay particular attention to Figure 4.

    http://www.ti.com/lit/an/sboa016/sboa016.pdf

    Even though the application note recommends making the differential capacitor 500 times the size of the common-mode capacitors, we believe that a ratio of 10 is still effective and a bit more realistic with respect to PCB layout and finding components.  In the end it really depends on the customer's system and requirements.  Nonetheless, the underlying theory behind your question is discussed.

  • 0 in reply to Pete%20Semig
    TI__Intellectual 2230 points

    Pete,

    Thanks. this pdf file is very helpful!