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Schematic Review for PT1000 using ADS1261-Q1

Ravi Chawda
Prodigy 80 points
Part Number: ADS1261-Q1
Other Parts Discussed in Thread: TS5A3159

We are using ads1261-q1 for sensing PT1000.The intended Temperature range is from -25°c to 130°c. The resistance at 130°c is 1500 ohms.

Pls. review the attached schematic and let me your valuable feedback.I have done the calculations as per the datasheet.Also Pls. let me know which Schottky Diode is recommended my Schematics.

We will set the PGA Gain as 8.

My Email ID is : ravi.chawda@threemediatech.com

  • 0
    TI__Guru 62825 points

    Hello,

    The schematic in general looks good and the supply connections and decoupling and input connections, biasing, and filtering also look appropriate.  Because the excitation currents are a low 100uA, the max leakage of the TS5A3159 over temp may cause a small mismatch between the lead resistance cancelling for the PT1000. The mismatch will not cause a measurement gain error because of the high-side reference configuration. 

    Here are a few good resources that you will likely find useful as well:

    A Basic Guide to RTD Measurements:
    http://www.ti.com/lit/an/sbaa275/sbaa275.pdf

    Three-wire PT100 RTD measurement circuit with high-side reference and two IDAC current sources:
    http://www.ti.com/lit/an/sbaa310/sbaa310.pdf 

  • 0 in reply to Collin Wells
    Prodigy 80 points

    Hello Sir,

    Thanks for your quick reply.It would be really nice of you if can pls. suggest an appropriate Sckotty Diode. or the parameters that must be considered in selecting the diode so that the it doesn't hamper the working of the RTD Measurement.

    Presently I am switching the IDAC2.Will it be OK if I Switch any one of the Analog inputs instead of Current Channels to resolve the mismatch problem.

    Since we are using 3 Wire PT1000 is it possible to design with higher Excitation Currents so that the leakage current problem can be still reduced.

    It would be great if you can share the any reference Schematics where we can use higher Excitation Current with PT1000.

    I have already read the both the useful documents shared by you.

    Thanks and Regards,

    Ravi Chawda

  • 0
    TI__Guru 62825 points

    Hello,

    There isn't any "secret sauce" in the diode selection here and pretty much any will work provided:

    1.)  Make sure that the forward voltage is low enough such that you don't run into IDAC compliance issues at the maximum PT1000 resistances and

    2.)  That the reverse leakage is low enough that it doesn't interfere with your measurements.  Since it looks like you have several volts of AVDD head-room you may consider a standard diode as the reverse leakage currents may be lower.