• State Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 1 answer
  • Subscribers 46 subscribers
  • Views 340 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

ADS1248: External voltage reference and excitation current sources

Dennis McGlumphy
Expert 1390 points
Part Number: ADS1248
Other Parts Discussed in Thread: ADS124S06

Dear Sirs

I'm considering using the ADS1248 ADC for a bridge type pressure sensor.  To get the best dynamic range, I intend to use an external voltage reference.  In addition, I would like to use the excitation current sources for the bridge excitation.  In the data sheet, section 9.3.8, it indicates that the internal reference must be turned on.  Does this mean I can't use the external reference or can both internal and external references be used at the same time, one for the ADC and one for the excitation current sources? 

  • 0
    TI__Mastermind 47625 points

    Hi Dennis,

    Great question!

    If you take a look at page 59 of the datasheet, section 9.6.4.3 MUX1—Multiplexer Control Register 1 (offset = 02h) [reset = x0h], and look at bit[6:5] and bit[4:3] you will see your options. As noted in the description for bit[6:5], in order to generate the IDAC current, the internal reference must be turned on. Then if you look at the description for bit[4:3], you'll see that you have four options for which reference the ADC uses for measurement:

    Reference Select Control

    These bits select the reference input for the ADC.

    00: REFP0 and REFN0 reference inputs selected (default)

    01: REFP1 and REFN1 reference inputs selected (ADS1248 only)

    10: Internal reference selected

    11: Internal reference selected and internally connected to REFP0 and REFN0 input pins

    If you haven't seen it yet, I encourage you to peruse A Basic Guide to RTD Measurements, located here: http://www.ti.com/lit/an/sbaa275/sbaa275.pdf

  • 0 in reply to Alexander Smith
    TI__Mastermind 20835 points

    Hi Dennis,

    one additional note. In case you haven't made your ADC selection yet then I would recommend to look at ADS124S06. This is our latest generation in that ADC family which offers many improvements over the ADS1248. You will also be able to achieve better accuracy and resolution with the ADS124S06 compared to ADS1248.

    Regards,

  • 0 in reply to Joachim Wuerker
    Expert 1390 points

    Dear Mr. Wurker

    Thank you for the heads up on the new part.  I do see some of the advantages of the ADS124S, particularly the external reference voltage can now go to the analog voltage rails.  This will help my dynamic range.  P.S. sorry I have no umlaut for the u. 

  • 0 in reply to Alexander Smith
    Expert 1390 points

    Dear Mr. Smith

    Thank you for the help.

  • 0 in reply to Dennis McGlumphy
    TI__Mastermind 20835 points

    Dear Mr. McGlumphy,

    your observation is spot on. That is one of the many improvements we made.
    Extending the external reference input voltage range up to the analog supply was mainly driven by the need for ratiometric bridge sensor measurements where the supply is used as the excitation for the bridge.

    And no worries about the 'ü'. None of my colleagues here in the US have that on their keyboards :-).

    Regards,