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ADS1278-SP: Read multiple RTD's

Art Mecina
Genius 16655 points
Part Number: ADS1278-SP
Other Parts Discussed in Thread: ADS1282-SP, ADC128S102QML-SP, LMP2012QML-SP, OPA333

Hello Guys,

Good day.

Our customer is considering to use ADS1278-SP to read three 2-wire RTDs connected to it. Since this device is not multiplexed, Is this possible for this device? is simultaneous measurement of these RTD's even possible?

His concern is sourcing the current to the RTDs. In multiplexed ADCs, the internal current source is sourced sequentially to each channel.

If this device is not possible for this use case, do we have any RAD HARD ADCs that would work with RTDs and have external reference and can source current?

Thanks in advance!

Art

  • 0
    TI__Mastermind 46880 points

    Hello Art,

    The ADS1278-SP has 8 simultaneous sampling ADC's inside, so yes, it can simultaneously sample up to 8 channels.  Each of the inputs would likely require an input amplifier driver, and there are no internal current sources for direct connection to an RTD; this would need to be implemented in external circuitry.

    The only other radiation hardened precision ADC's that I am aware of are the ADS1282-SP and ADC128S102QML-SP. 

    The ADS1282-SP is another 24b ADC that includes an internal PGA amplifier, 2 channel mux, and could be direct connected to an RTD.  However, it would still require an external current source.  Plus, it only has one ADC inside, so for simultaneous sampling you would need 3 of these ADC's, plus external current sources.

    The ADC128S102QML-SP is a 12b SAR ADC and includes an 8 channel multiplexor, so if the customer does not need simultaneous sampling, this part may be an option.  It will also require an external current source for the RTD's, plus an input amplifier.

    Regards,
    Keith Nicholas
    Precision ADC Applications

  • 0 in reply to Keith Nicholas
    TI__Genius 16655 points

    Thanks Keith!

    You mentioned an external current source. Do you have suggestions for any external current source preferably rad-hard that can be use?

    Art

  • 0 in reply to Art Mecina
    TI__Mastermind 46880 points

    Hello Art,

    Take a look at the OPA333 datasheet, Figure 20.  This is a good example on how to build a precision current source.  Although the OPA333 is not available in rad-hard, the similar LMP2012QML-SP is and could be used in a similar circuit.

    Regards,
    Keith

  • 0 in reply to Keith Nicholas
    TI__Genius 16655 points

    Thank you very much Keith!

    Fyi only for those who would refer to this ticket in the future. The Space grade variants of the devices mentioned above are the following:

    ADS1282-SP
    ADC128S102QML-SP
    LMP2012QML-SP

    Art