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ADS1248 IEXC

Kazem Eghtesad
Prodigy 20 points
Other Parts Discussed in Thread: ADS1248

Hi,

We are using the ADS1248 for the RTD measurement with ratio-metric configuration. While debugging the conversion, I understood that writing to MUX1 BITS 2:0 to read the external REF0 (101) fails and reads 0. The only reason could be that the IEXC shuts down. In the datasheet, it is mentioned that "The MUXCAL selection supersedes selections from registers MUX0 and MUX1 (MUX_SP, MUX_SN, and VBIAS)." Why does IEXC shut down?

Is there any other way to be able to measure the REF0 in such configuration?

Regards.

Kazem.

  • 0
    TI__Guru* 98015 points
    Kazem,


    I can check the IEXC on my setup during the condition, but the MUXCAL settings are primarily used as a diagnostic to make sure the system is working. It therefore takes over a lot of the internal configuration to make sure it gets the proper measurement.

    If IEXC shuts off during the MUXCAL measurement, I would suggest making a measurement of a stable input with the REF0, and then quickly switching to making the same measurement with the internal reference. As long as the measurement input is the same, the ratio of the first and the second measurement will be the inverse of the ratio of the reference voltages.

    You may be able to do this with the internal temperature sensor. I would check if first before using it.


    Joseph Wu
  • 0
    TI__Guru* 98015 points

    Kazem,


    A colleague just told me that MUXCAL does not turn off the IEXC current. I would check to see if you are not accidentally shutting it off, rerouting it to another pin, changing the value, or turning off the internal reference (the IDAC requires the internal reference for operation).

    Joseph Wu