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INA186: RCV420

Arun Ashok
Prodigy 90 points
Part Number: INA186
Other Parts Discussed in Thread: RCV420

I am looking to build a 4-20mA to 0-3.3V conversion circuit. The 4-20 mA input is generated by loop powered / externally powered (24V) process control transmitters (eg https://rishabh.co.in/uploads/product/Datasheet_-_CT_with_inbuilt_Transducer_Ver_C1.pdf page 4). The 0-3.3V output is to be interfaced to ADCs. I was thinking about RCV420 or INA186 based solution (4-20mA goes through a shunt R -> this is fed to the input of INA186) and I liked the block diagram on the first page of INA186 datasheet - it looks very clean and does not have the thermal drift problems associated with RCV420. However I am a bit hesitant to use the circuit as shown on the datasheet because there is no isolation between the 24V from the sensor and 3.3V from my microcontroller. Can you suggest any alternate solution than can do 4-20 mA to 3.3V conversion, but also provides isolation ? 

Thanks.

  • 0
    TI__Mastermind 26475 points

    Hello Arun,
    The output is powered by the supply voltage and cannot go above supply voltage.  You can see the datasheet the swing high is limited by VS.  The input stage VCM will not impact the output much and is in the order of 0.1µV/V VOS error.  We have input circuitry that separates the Voltage at the input to the output.  It is not completely isolation as the input cannot go beyond the 40V VCM.  If your input voltage is limited to the 24V you mentioned I do not see and issue and I would power the INA186 with a 3.3V to assure that the output does not go beyond that value.