• State Resolved
  • Replies 4 replies
  • Subscribers 47 subscribers
  • Views 68 views
  • Users 0 members are here
Support feedback
Options
Options
Related

ADS124S08: An issue where DRDY does not changed to LOW

Joohwan Chae
Prodigy 60 points
Part Number: ADS124S08


I have implemented a program to read ADC values using the ADS124S08.
It operates in continuous conversion mode.


We are using three ADS124S08 chips, and they are selected sequentially.
For each chip, the MUX and IDAC settings are changed to read ADC values from three different sensor channels.
For a given sensor channel, after setting the MUX, the program waits for data conversion and reads the ADC values using the RDATA command when DRDY goes LOW.

However, if DRDY does not go LOW for more than 500 ms after MUX channel setting, the program make the corresponding ADC chip is reset, and moves on to the next chip's sensor channel.
The reset procedure is the same as the initial initialization: a WAKEUP command, followed by a RESET command, and the rewriting all registers.

SPI communication for register writes and commands appears to be working correctly, but there have been cases where DRDY does not go LOW for more than one hour.
During that time, it seems that reset attempts were continuously made.
After that one hour period, ADC values were observed to be read normally again.

Are there any points or possible causes that we should check or investigate further in this situation?

  • 0
    Prodigy 60 points

    I set SPS = 20, so I expected the DRDY (HIGH period) to correspond to a conversion time of about 50 ms.

  • +1 in reply to Joohwan Chae
    TI__Guru 54366 points

    Hi Joohwan Chae,

    I am not sure why this would happen. Some questions:

    • Are you saying that one ADC randomly stops toggling DRDY for up to one hour?
    • Is it always only one ADC? If yes, it is always the same ADC, or can this occur on any of the three ADCs? 
    • After one hour then the ADC starts operating correctly again? If so, do you need to do anything to get it to work correctly, or does it just randomly start working again?
    • Does this condition always last one hour, or can it be much shorter?
    • If you power cycle the board / ADC instead of just resetting, does the ADC work again immediately?
    • How are you controlling conversions? Using the START pin or the START command?
    • Can you share a schematic?
    • Can you still read / write registers during the time when the DRDY pin stops toggling?

    There is no obvious reason why the ADC would stop functioning randomly for one hour then start functioning properly again

    Also, please note that over the next two weeks you will receive limited support on e2e due to the national holidays in the US. Thanks for your patience

    -Bryan

  • 0 in reply to Bryan Lizon86
    Prodigy 60 points

    Thank you for your reply.

    So far, this issue has occured only once, and it happened on only one of the three ADCs, where DRDY did not go LOW for about one and half hours.

    As mentioned earlier, the firmware is designed to reset the ADC whenever DRDY does not go LOW within 500ms, so SPI communication should have been performed repeatedly. Because of this, it seems that the ADC itself was not completely non-functional, but rather that only the DRDY signal was not behaving
    correctly.

    After about one hour, the ADC recovered on its own without any additional action.
    When the system was operated again the next day, this issue was not observed again.
    However, we are concerned that it could recur, so we wanted to ask for advice.

    In this situation, would it be reasonable to consider this as a defective ADC device, or are there other possibilities we should consider?

  • 0 in reply to Joohwan Chae
    TI__Expert 3375 points

    Hi, 

    Due to the holidays, please expect a delay in response. We will address your question when we return in the new year. 

    Thanks,

    Maggie