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INA3221: Question of AC Response of the INA3221

Wayne Chen
Guru 16055 points
Part Number: INA3221

Hi Sirs,

According to the frequency response chart of the INA3221 datasheet, the gain starts dropping at 200Hz. Can I say that the INA3221 cannot determine transient signals above 200Hz? Is it a PGA or ADC limitation?



Thank you and Best regards,

Wayne Chen
03/31/2023

  • +1
    TI__Expert 4720 points

    Hello,

    That is the ADC's Frequency Response. You are limited by the ADC conversion time and averaging you program. The device can update at a rate of 140us with an average of 1. This will be for only shunt continuous. If you also add the Vbus measurement at 140us you will update the measurements at 280us. Similarly with adding more channels and averaging.

    Regards,

    Cas

  • +1 in reply to Castrense Nigrelli
    Guru 140200 points

    Hi Wayne,

    to answer an eventual follow-up question, section 8.4.3 of dataaheet explains that the INA3221 internally works with oversampling. This means that a low pass filter with a corner frequency well below 1kHz has not to be added at the inputs of INA3221 to prevent aliasing artefacts.

    Nevertheless, adding a low pass filter with a corner frequency like shown in figure 26 can be very helpful.

    Kai

  • 0 in reply to Castrense Nigrelli
    Guru 16055 points

    Hi Cas, Since there is attenuation above 200Hz with the ADC, should we compensate the gain from the Vshunt and Vbus readings continuously? Thanks a lot...Wayne Chen

  • +1 in reply to Wayne Chen
    TI__Expert 4720 points

    Hello,

    No, as Kai tried to explain the INA3221 works by oversampling, the sampling frequency of the ADC is 500kHz the decimating and noise reduction filter are there to reduce the noise associated with making the measurement.

    As Kai also mentioned there are instances where you might want to have an input filter which is explained in the second paragraph of section 8.4.3.

    Regards,

    Cas