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INA226 ADC consideration

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Other Parts Discussed in Thread: INA226

Hi

We have questions about INA226Q1.

1. What is the purpose of filtering at ADC input? Is this filter needed anytime?

2. Can we change the full-scale range of Bus voltage (40.96V)?

BestRegards

  • Hello na na 78,

    1)The filtering is required to help filter transients at harmonics of the sampling frequency of the ADC which is 500kHz (+/- 30%). There is a section on the datasheet (7.4.2 ) that goes more in detail on this.

    2)The full-scale range of the Bus voltage cannot be changed.

    Regards,
    Javier
  • Hi Javier

    Thank you for your reply.

    We had additional questions about averaging function.

    3) Is the averaging mode using moving average?

    4) We may consider following two cases.

    I. Number of Averages : 1, Conversion time (Vbus) : 588us, Conversion time (Shunt) : 588us
    -> 1.176msec

    II. Number of Averages : 4, Conversion time (Vbus) : 140us, Conversion time (Shunt) : 140us
    ->1.120msec

    These results are almost the same.
    Are there any differences between increasing the number of averages and increasing conversion time?

    BestRegards
  • Hi na na78,

    Averaging and Conversion Time considerations are explained in section 7.4.1 of the datasheet. Please review and let me know if you have further questions.

    Regards,
  • Hi Mayrim

    Thank you for your reply.

    We understand that the conversion time and number of averages can be used to estimate the time of data updating to register.

    So, is it possible to know actual data sampling time? (not conversion time)
    Is that fixed by ADC sample rate (500KHz)?

    Best Regards
  • Hi na na78,

    It is not possible. The internal ADC has a delta-sigma architecture which does not support separation of sampling and conversion phases. What the datasheet shows is the total time elapsed between readings, not the actual time spent converting the sampled input.

    Regards,
  • Hi Mayrim,

    what is the ADC specific(to consider) time during the signal have to be stable to be measured? I have to measure dynamics currents on my MCU. I know about the conversion times, but my question is focusing in to fastest measures,  If ADC conversion time is 140us, how long the ADC take to get the value before convert and write all register(shubtV,BusV,current...)? 

    thank you in advance.

    Ricardo.

  • Hi Ricardo,

    I apologize for the delay. The INA226 is a low bandwidth device (only about 400Hz according to figure 1 of datasheet) that is intended for precise DC current measurements. So to begin with I would not recommend it for your application. Also, input signal stability during sampling is not a major concern with this device because of the relatively low input switching frequency (max 650kHz according to section 7.4.2). Even with a sampling cap value of 10pF (gross over-estimate) the input impedance would be about 24kOhm, which would result in less than 0.05% input voltage droop with a 10ohm source resistance. In addition, adding a large 0.1uF to 1uF input bypass cap, as recommended in the datasheet, will decrease the source impedance at high frequencies and reduce the droop even further.

    Best Regards,
    Harsha Munikoti