• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 46 subscribers
  • Views 616 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ADS1247 datasheet filter calculation

Jose M Fernandez
Prodigy 110 points
Other Parts Discussed in Thread: ADS1247

Hello.

                     I am going to use ADS1247 in a new design. I have been looking at the datasheet to choose the right component values. I will use 3-wire RTD configuration. All is fine for me in the datasheet except the calculation of   CI_DIFF capacitor. I don´t know why the value chosen for RTD is 150 ohm to do this calculation. Somebody could explain why RTD=150?

                      Thank you in advance!!

  • 0
    Prodigy 110 points
    Hello again. Sorry, I forgot to ask why for the calculation of CR_DIFF, the value of RTD is used. I think the value that should be used for this calculation is Rref=820 instead of RTD. Am I wrong?

    Please, don´t forget to reply to this question and to the first one.

    Thank you very much.
  • 0 in reply to Jose M Fernandez
    TI__Guru* 97775 points
    Jose,


    For the first question, 150Ω was used as a place holder. In the end, the RTD will be anything in the range from 20Ω to 400Ω, so that in combination two 4.7kΩ resistors will still look like the two 4.7kΩ resistors.

    For the second question, you are correct. The RRTD should be replaced by RREF to calculate the frequency response of the filter. Again, the CR_DIFF will be dominated by the filter resistors and not the RREF.

    If you're interested, there may be more detailed analysis in a different application note. It's similar, as the application in the datasheet was derived from this note, and there's a bit more explanation.

    www.ti.com/.../slau520a.pdf



    Joseph Wu