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I'm wanting to current sense a 10A load with high precision. I'm planning to use a current shunt resistor and then amplify/filter this signal before sending it to an ADC. Which design flow is typically more precise?

  1. Using a high precision differential op-amp (amplify + level shift) -> buffer -> RC filter -> ADC
  2. Using an RC filter -> internal PGA of an ADC to amplify the signal, for example, the ADS131M02IPWT, datasheet

The intuitive answer is #1, but then I'm wondering why most ADCs have a PGA stage, because it's good enough for the typical application?

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    \$\begingroup\$ What does "high precision" mean to you?? \$\endgroup\$
    – Scott Seidman
    May 30 at 19:22
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    \$\begingroup\$ I'm trying to achieve <1% error for an energy measurement. \$\endgroup\$
    – ken
    May 30 at 19:28
  • \$\begingroup\$ Is the current sense resistor referred to ground, the same ground as the ADC? If not, what is its voltage with respect ground? \$\endgroup\$
    – Davide Andrea
    May 30 at 19:28
  • \$\begingroup\$ My application is AC and I'm putting the sense resistor on Neutral. \$\endgroup\$
    – ken
    May 30 at 19:38
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    \$\begingroup\$ You can easily get <1% with either approach. #1 requires more parts, #2 gives you less flexibility on the input signal. Whichever you choose be careful if you are planning on building these for any length of time; specialized, single-source parts like the one you mentioned can have a tendency to become hard to get. I would use a popular ADC with a big user base as a basis for your decision. \$\endgroup\$
    – John Birckhead
    May 30 at 19:50

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I'm trying to achieve <1% error

Then you should use a Hall Effect sensor instead:

  • isolated
  • 1 % accurate
  • Outputs 0 to 5 V, same as the input range of your ADC.
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  • \$\begingroup\$ I'm considering cost so I have to go with a shunt resistor - I'd rather spend more on a better op-amp/ADC than going with other sensing techniques. \$\endgroup\$
    – ken
    May 30 at 19:34

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