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ADC's Input channels-Analog Isolation

Sharvy Mayan
Intellectual 680 points
Other Parts Discussed in Thread: AMC1200, AMC1100, ISO122, ISO124

Dear All,

Our recent requirement is to have a channel Isolation of 1000 V between each channels in the 8 ADC inputs. It is a single ended input with the given values as 0-100V or 0-4V or 0-100mV o r 4-20mA input channels.

Please let me know,

  1. The best  suited Analog Isolator ( Isolation Amplifier) for our application from TI ?
  2. Which isolator is good for our application. Isolation amplifier with Optical barrier or Capacitive barrier?

Best Regards

Sharvy

  • 0
    TI__Guru**** 180961 points
    Hi Sharvy,

    The AMC1100 and AMC1200 are both analog isolation amplifiers that could potentially be suited to work for your 0-100V range and 0-4V range. These amplifiers have a differential output, so depending on your ADC, you may have some additional signal conditioning to do. The 100mV and 4-20 mA requirements would be a little harder to accommodate. What sort of application is this for?
  • 0 in reply to Tom Hendrick
    Intellectual 680 points

    Dear Tom,

    Thanks for the feedback.

    We will do some signal conditioning before we apply the analog inputs to the Isolation Amplifier. And the signal amplitude will be restricted to 0-5V or 0-10V accordingly. For 100mV we are planning to use some Op-amp with Gain more than 20.

    1. Whether the suggested device will support single ended signal too?
    2. If so, the grounding on the Negative polarity pin will be enough for the working of the device as single ended?
    3. Do I need a dedicated power supply for the each AM1xxx devices? Since we have 8 Analog channels and channel to channel Isolation is required.

    This analog card can be used to read real time information's from  the Devices ( Transformers, Temperature sensors etc ) used  in Oil/Gas field.

    Best Regards

    Sharvy

  • 0 in reply to Sharvy Mayan
    TI__Guru**** 180961 points

    Hi Sharvy,

    You could tie the (-) inputs to the isolated GND, but the output is also differential, so you would need to accommodate that somehow.  If you need channel to channel isolation, than the entire signal path for all eight channels would need its own power supply, not just the AMC1xxx devices.  Also, the AMC1xxx devices input range is +/-250mV, so your signal condition inputs would need to be scaled accordingly.

  • 0 in reply to Tom Hendrick
    Intellectual 680 points
    Dear Tom,

    Could you please suggest me, if you have any Isolation Amplifier category which supports single ended input/output with 0-3.3V or 0-5V input voltage limit.

    Best Regards
    Sharvy
  • 0 in reply to Sharvy Mayan
    TI__Guru**** 180961 points

    Hi Sharvy,

    The ISO122 and ISO124 might be of interest to you if you already have bi-polar supplies available on your analog front end. 

  • 0 in reply to Tom Hendrick
    Intellectual 680 points

    Dear Tom,

    I don't have the bipolar supply option in my board. I have  Isoated +3.3V supply. Is it possible to operate the ISO124 , if i connect the Ground terminal ( 0V potential ) of my Isolated power supply to the -VS1 pin of the ISO124?.

    Below is my reference circuit. Will it work with single ended supply and single ended input?

    Best Regards

    Sharvy

  • 0 in reply to Sharvy Mayan
    TI__Guru**** 180961 points

    Hi Sharvy,

    Unfortunately no, the ISO124 needs minimum +/-4.5V to operate properly.  The -VS1 rail cannot be tied to ground.

  • 0 in reply to Tom Hendrick
    Intellectual 680 points

    Dear Tom,

    Thanks for the continuous support.

    Please clarify the below doubt too.

    Lets consider the scenario: ISO 124 supplied with +5V and -5V

    • As I informed you earlier, my Input ranges are between 0V & 3.3 V or 5 V . But as per the datasheet of ISO124 , the Input voltage minimum range given as +/-10 V. Does that mean, I can apply any voltage in between -10V to +10V?

    • Do I can feed the VS1 & VS2 with different Voltages?

    Best Regards

    Sharvy