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INA237: Which ADC input range to use?

Marcello Deluca
Prodigy 210 points
Part Number: INA237

Tool/software:

Is there data missing from data sheet to help me determine which ADC Range I should design for? On the diff'l input I am using current sense resistors and I would assume using the high ADC range (160mV max) I would get better results (better SNR & more accuracy) than using the low range - but there are no specs in the data sheet that relate to the ADC range and how it affects the specs

  • 0
    TI__Mastermind 22035 points

    Hello Marcello,

    There are multiple factors that go into choosing which range you want to use. Here are a few key points:

    Shunt restrictions:

    If you are limited to a specific size shunt, or small range of shunt resistors, then you want to pick the ADC range that you utilize the best. For accuracy, ideally you want your maximum expected current to closely max out the ADC range. 

    Power considerations:

    If you are in a power sensitive design, then you'll want as small a shunt resistor as you can get away with, in which case you will want to use the smaller ADCRANGE since you will likely have a smaller differential voltage. If power is not a concern, then larger shunt resistors can be used. 

    The noise performance of the INA237: 

    For this, you'll want to use Table 8-2 in the datasheet which shows the noise performance for each ADC setting based on your configuration settings (this is likely the info you were looking for about how ADC range affects the specs). You can use this table to find out which ADC range gives you better accuracy based on your setup.

    If you can be flexible with your shunt size, then you want to get this value as high as possible (so generally the higher ADC range will give you better results with an ideal shunt, unless both ranges are maxed out at 16 bits).

    If you are stuck using one specific size shunt, then note that the smaller ADC range is smaller by a factor of 4, which would be 2 bits. So, with the same size shunt if the difference between ENOB of the two ranges is 2 (ie, 13.7 and 15.7), then the accuracy is the same. If the difference is greater than 2, then the larger range is better, but if the difference is less than 2 then the smaller range is better.

    For this reason, some people design for the larger range, then "zoom in" to the smaller range when measuring smaller values that fit within the smaller ADC range to increase the accuracy of those measurements (if the ENOB for their acceptable conversion and average settings makes it so that the zoomed in mode gives higher precision than when zoomed out).

    Regards,

    Mitch