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ADS131M08: Implementing a Current loop receiver

Manu Abraham
Genius 3510 points
Part Number: ADS131M08
Other Parts Discussed in Thread: XTR117, ADS125H02, AMC7836

Hi,

Greetings!

I am trying to implement a standard Current Loop receiver with the ADS131M08.

Does the ADC need an opamp at the input stage, or is that something that can be got away with ?

Thanks,

Manu

  • 0
    TI__Guru 67206 points

    Hi Manu,

    Thank you for your post.

    Current sensing circuits can be interfaced directly with the ADS131M08. Some examples of the passive components typically used are shown in the applications section of the data sheet (Section 9.2).

    What are you using to measure the current?

    Regards,

  • 0 in reply to Ryan Andrews
    Genius 3510 points

    Hi Ryan,

    Greetings!

    Having seen that figure, the possibility/thought of interfacing directly to a 4-20mA Loop powered current loop transmitter (eg: XTR117 and the likes) drew a bit more closer.

    But wondered whether any conditioning of the loop was necessary and hence the original question.

    Another question that did come up, whether the ADC input would require any input protection using a TVS diode and so on.

    Thanks,

    Manu

  • 0 in reply to Manu Abraham
    TI__Guru 67206 points

    Hi Manu,

    Thanks for clarifying. I'll get back to you with some additional recommendations.

    Regards,

  • 0 in reply to Ryan Andrews
    TI__Guru 67206 points

    Hello Manu,

    Thanks for your patience.

    Could you help us understand more of your application requirements?

    1. How many loop inputs do you need to measure?
    2. Update rate per channel?
    3. What size shunt are you trying to use?
    4. Are there common-mode voltage differences between channels?

    Another device to consider might be our ADS125H02.

    Best regards,

  • 0 in reply to Ryan Andrews
    Genius 3510 points

    Hi Ryan,

    The more the number of inputs the merrier. I was intending of using a few ADC's for a total sum of 30 inputs

    (I had previously looked at the AMC7836, but that one had a resolution of 12bits alone. The 21 channels were interesting, though it was only multiplexed. After many thoughts and iterations, the ADS131M08 appeared to be saying; me, me, I am good to go in all senses.) :-)

    The idea was to use 4x ADS131M08 for the application. Any 8x input appeared to be a good choice.

    As far as signal update rate, that's quite low (After averaging and decimation), but whatever best possible is good enough.

    (Was intending to use Oversampling & Decimation using the Digital decimation filter)

    With a 3.3V input and 4-20mA input signal, the shunt should be around 165 ohms.

    Common Mode differential shouldn't be a big issue, but the cables from the sensors themselves when bundled together could likely form a little Transmission Line ?

    The only downside with the ADS131M08 was the lower input voltage, where I couldn't find much of a choice regarding a TVS diode. I did find a PESD3V3L from NXP though, it might not be the ideal choice.

    Thanks,

    Manu