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ADS124S08: chip internal temperature sensor issue

Andrey Chuykin
Prodigy 20 points
Part Number: ADS124S08

No system monitor signals can be measured. Neither the internal temperature sensor nor the analogue supply voltage. The measurement result is 0 mV in any case.
The pins signals (AIN0-AIN7) are measured perfectly.
I utilize the internal reference. The reference buffers are switched off. Register REF value setted up to 0x3A.
While measuring the voltage at AIN0-AIN7 pins the register SYS set up to 0x15.
To measure the monitor signals I set the SYS to 0x55 for measuring temperature and 0x75 for measuring analog supply voltage.
What is the issue? What am I doing wrong?

  • 0
    TI__Guru** 113765 points

    Hi Andrey,

    Welcome to the E2E forum!  The settings you are using would be appropriate, but could I see all of your register settings?  Have you verified with an oscilloscope or logic analyzer that the register setting you are using is being transmitted correctly to the SYS register?  If so, can you send me a screen shot of the communication?

    The internal temperature sensor requires that the PGA be enabled and that the gain be in the range of 1 to 4.

    Another consideration is whether you are waiting long enough after the SYS register change for the conversion to complete.  How are you monitoring DRDY for conversion ready?  Also, if you are using single conversion mode, you must send the START command to initiate the conversion.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 20 points

    Hi Bob

    Thank you for your time you've spent. 

    But the issue was in Global Chop Mode. When it is enabled, the internal temperature or supply voltage measurement returns a zero result. I turn off this mode for the duration of the internal sensor temperature measurement.

    Unfortunately, I have not found any mention of this feature in the datasheet.

  • 0 in reply to Andrey Chuykin
    TI__Guru** 113765 points

    Hi Andrey,

    I'm glad you discovered the solution to the issue you were having.  This is very good information and not the behavior I would have expected either.  We will see what we can add to the datasheet to make this more clear.

    Best regards,

    Bob B