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ADS124S08: ADC Reset during continuous mode.

Joohwan Chae
Prodigy 60 points

Part Number: ADS124S08
Other Parts Discussed in Thread: ADS1248

We configured the ADS124S08 ADC to operate in continuous conversion mode with the START pin held HIGH at all times. However, when it becomes necessary to reset the ADC during operation and a RESET command is issued, the data conversion is remains stopped even though the START pin is still HIGH.

According to the datasheet, after a reset the device enters a standby state and does not resume conversions until it detects either a rising edge on the START pin or a START command.

In this case, if the START pin is intended to remain HIGH continuously, is it correct that we should use the START command to restart data convserion?

  • 0
    TI__Mastermind 25105 points

    Hi Joohwan,

    is the START pin controlled by an MCU in your case or did you tie the START pin to IOVDD permanently?

    Please note that if you tie the START pin to IOVDD permanently, the device might or might not start converting after power-up. Also after a device reset, the START pin needs a rising edge for the ADC to start converting again as you correctly stated.

    Sending the START command after a device reset, when the START pin is held high, might work. But I don't know for sure, because the START command might not get decoded when the START pin is held high.

    Is there a specific reason why you need to tie the START pin high?

    Regards,
    Joachim Wuerker

  • 0 in reply to Joachim Wuerker
    Prodigy 60 points

    the START pin is controlled by an MCU.

    We need to tie the START pin high because we are using continuous conversion mode.

  • 0 in reply to Joohwan Chae
    TI__Mastermind 25105 points

    Hi Joohwan,

    thanks for the clarification.
    I might have mixed up the behavior with our newer ADCs, such as ADS124S08.
    Sending the START command after a device reset with the START pin set high should start conversions. If it doesn't, then maybe sending the SLEEP and WAKEUP commands might be required.

    Regards,
    Joachim Wuerker

  • 0 in reply to Joachim Wuerker
    Prodigy 60 points

    Thank you for your reply.

    We have another concern.

    After issuing the RESET command, we confirmed that data conversion starts correctly by using only the START command while keeping the START pin held HIGH.

    However, as you mentioned, is there any possibility that the START command might not be decoded correctly when the START pin is already HIGH?

    That is our main concern.

  • +1 in reply to Joohwan Chae
    TI__Mastermind 25105 points

    Hi Joohwan,

    let me revise my previous comment as I mixed the device up with the older ADS1248.
    With ADS124S08 you don't need to take the START pin high constantly to operate the device in continuous-conversion mode. This was the case in the old ADS1248.
    If you don't want to control conversions using the START pin on ADS124S08, then I suggest to keep the START pin always low and only start and stop conversions using commands. That way you also don't have issues after a device reset.

    Regards,
    Joachim Wuerker