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Measuring a 2V battery on a 40-80V Common mode across an isolation boundary

Aaron Jones
Intellectual 760 points
Other Parts Discussed in Thread: ISO124

Hi Team,

I have a customer that's looking to measure a 2V battery on top of a 40-80V common mode. The entire system is floating, so isolated signal delivery is necessary. Ideally, the battery can be measured down to 0V.  We're looking at the ISO124 isolated amplifier, as well as isolated ADCs and non-isolated ADCs coupled with discrete digital isolators, but I was wondering if there was a recommended method to achieve this.

My thoughts:

  • The isolated ADCs look promising, but they can't handle 2V differential, only 250mV.
  • Discrete ADCs/Isolation/references/buffers/MCU add to bom count significantly
  • isolated amplifiers are unwieldy, can't handle the common mode by themselves, and are expensive.

Thanks for all of your input!

  • 0
    TI__Guru 62085 points
    Hi Aaron,

    Thanks for the information. I agree with all your points. The easiest solution is likely going to be to use the isolated ADCs that you've found (AMC12xx / AMC13xx) and to scale the input appropriately using an attenuating difference amplifier or resistive network. That said, this may not be the highest accuracy solution.

    Your 2nd bullet will likely provide the highest accuracy but with the greatest system complexity. Provide us some more information regarding the system requirements are and we can help identify the proper solution.