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ADS124S06: Temperature Measurement with ADS124S06IRHBT

Martin Holguin
Intellectual 310 points
Part Number: ADS124S06

Hi everyone,

I've read a lot about these converters and other application notes from your website to try to design this without dying in the process. Could you give me some advice if something is wrong? Perhaps some recommendations or point out any errors?

Note: All resistors without a specified value are 50 ohms. Additionally, I read that AINCOM is only used for single-ended measurements, but as things often go wrong when I start a new design, I decided to place a 0-ohm resistor there, unsoldered, to connect it to GND. Also, AGND and GND are connected. I designed the circuit to measure a PT100 in a range from -10°C to 100°C.

  • 0
    TI__Guru** 113765 points

    Hi Martin,

    The only real issue is the REFN0 input filter resistor.  This will add an error with the reference buffer turned off (as required when connected to AVSS) so the R7 should be replaced with a 0 Ohm resistor or directly connected to AVSS (AGND).  C2 should be a DNP or removed.

    It is not clear the temperature coefficient of the reference resistor R1.  This resistor should be 10ppm drift or better.

    It is not clear what current you are intending on using for the IDAC, but the minimum reference voltage is 0.5V, so you need to be at at least 500uA.

    AINCOM is actually the same as any other ADC input.  It may have been better to call this something different as it is often confused.

    In your circuit you have selected a series combination which means that the RTD must be connected for the circuit to work.  As you have additional pins available to connect an IDAC source to each of the RTDs independently, you can connect the RTDs independently by using the second reference input which would require an additional reference resistor or you can connect them in parallel.  The advantage is you don't require that both RTDs be connected for the measurement to be made.  This is helpful to isolate the RTDs in case there is a wire break.  See the circuit in A Basic Guide to RTD Measurements in section 2.9.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Intellectual 310 points

    Hi Bob,

    I'm glad to know all of this before sending it for manufacturing. I'll make modifications to my design as soon as possible, incorporating all the advice you provided. The 1.15K resistance seems to be correct, as I used a resistor with a 10ppm drift, and the current I'll be using is 1mA. I'll try to post the updated design as soon as possible to see if it might work better after these changes.