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ADS124S08: sometimes the value doubles

Marco Spiesecke
Prodigy 100 points
Part Number: ADS124S08


Hi,

we are using the ADS124S08 for longtime measurements. Within a Week suddenly the measured value doubles. Sometimes this error fixes itself after a while and sometimes it needs a hardware reset, reset via reset pin does not work. Is the ADS124S08 faulty or is there anything else I could do to test or avoid this error? 

  • 0
    TI__Guru** 113765 points

    Hi Marco,

    It sounds like you may be getting noise on the SPI SCLK line causing a bit-shift in the data.  Can you give me some examples of the actual data you are seeing (both before and after)?  A couple of things to note.  If you read data direct instead of using the RDATA command, this may cause some issue if noise occurs on the SPI SCLK line.  This may be especially true if you are holding CS low (like holding it logic low) instead of toggling CS.  Toggling CS between communication will help by resetting the SPI bus internal to the ADS124S08 following each communication.

    If you are holding CS low, then I would suggest that you enable the SPI timeout feature in the system control (SYS) register.  This bit will allow reset of the SPI bus if the communication is not valid for a specified period of time.

    How are you determining when to read the conversion data?  If you are using a polling or timer method as opposed to monitoring DRDY and using an interrupt driven system, then I would suggest using the RDATA command instead of reading the data direct.

    I find it interesting that the hardware RESET pin is not resetting the device.  How are you determining that the reset is not taking place? Are you making sure that you are holding the RESET pin low for the required time?  Due to capacitance on the line and the strength of your GPIO you may need to hold the output from the micro longer then expected to ensure that the device is seeing the required low time at the RESET pin of the ADS124S08.  You may want to verify the time with an oscilloscope.  You could also try the RESET command to see if the command works differently.

    The last possibility that I can think of is a transient event causing issues with the ADC.  You could monitor the POR flag in the status register to see if the device resets.  Depending on what is connected to the analog inputs, it is possible that ESD or some other large voltage transient can be causing the ADC to act in an unusual way.  You need to make sure that the Absolute Maximum Ratings as specified in the datasheet are not exceeded.  In particular the current and voltage maximums on the analog inputs.  I can be of more help if I know what type of sensor in connected and if I could see a schematic.

    Best regards,

    Bob B