• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 46 subscribers
  • Views 694 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ADS1278 SYNC Input Question

KAL CONLEY
Prodigy 40 points
Other Parts Discussed in Thread: ADS1278

Hello,

My understanding is that the SYNC input is only used to synchronize multiple devices with each other or to synchronize the device(s) to an external event. Can someone please provide any other situations (if any) that require the SYNC input to be used. For example, if the clock inputs are interrupted is asserting SYNC ever necessary with a single device? Also, the datasheet says: "For consistent performance, re-assert SYNC after device power-on when data first appear." Does this only refer to synchronizing multiple devices being used together after power-on?

We are using a single ADS1278 in our design which will run continuously. Is there any reason whatsoever that we wouldn't want to simply tie the SYNC pin to IOVDD?

Thanks,

Kal

  • 0
    TI__Mastermind 43915 points

    Hi Kal, 

    Synchronizing multiple devices or synchronizing to an external event are the major reasons you would use the /SYNC option. You have probably read this in the datasheet, but when you pulse the /SYNC, the conversion process is halted, and the digital filter is reset. You will notice that the ADS1278 uses a coefficient based FIR filter that uses a combination of 76 conversion (78 for high resolution mode) cycles before a fully settled value is output. /DRDY will stay high the entire time the digital filter is settling and will pulse low when the first settled data is available. This can become useful if you would like to trigger a new conversion period at some specific time. Note, it will take 76-78 conversion periods after pulsing the /SYNC to receiving newly settled data. During power up, the POR should clear out the digital filter, however, we recommend using the /SYNC after power up as well to clear out the digital filter in case there was an issue with the POR. We would not expect any issue, but we recommend it just to be safe. 

    In your application, you are going to run the ADS1278 continuously without any need to synchronize it to another device or an external event. You can tie the /SYNC pin high if you feel you will not need to reset the digital filter or sync the ADC to other devices. 

    Regards,

    Tony Calabria 

  • 0 in reply to Tony Calabria
    Prodigy 40 points

    Hi Tony,

    We are using the frame-sync interface, so instead of /DRDY pulsing low, DOUT will remain low for 76-78 conversions after /SYNC is asserted?

    Do you recommend using /SYNC when changing modes? I assume that changing modes causes the filter to be reset as well.

    What are the advantages during power-up to asserting /SYNC and waiting for DOUT over just ignoring the first 76-78 conversions?

    In particular I would like to use the following strategies for power-on/reset and for mode changes:

    --------

    POWER-UP: (1) Bring up power supplies. (2) Wait at least 2^18 clk cycles. (3) Wait for DOUT to have data. (4) Wait 76-78 conversions. (5) DATA is valid.

    MODE CHANGE: (1) Change Mode. (2) Wait for DOUT to be held low. (3) Wait for DOUT to have data. (4) DATA is valid.

    --------

    Thanks,

    Kal Conley

  • 0 in reply to KAL CONLEY
    TI__Mastermind 43915 points

    Hi Kal, 

    When you first power on the ADC, /DRDY should not go low until 76-78 conversions indicating a new data ready. You do not need to pulse a /SYNC after power on. I just recommended it to be on the safe side. 

    I am unsure whether the digital filter resets when changing from mode to mode (Low Power to High Resolution for example). My guess is that it would but am not sure, it may have been designed without this implementation. The datasheet does not state if the filter resets therefore I cannot draw any solid conclusion. In the datasheet we do recommend using the /SYNC to clear out the digital filter. If possible I would use this functionality to be safe in your design. If you decide not to use the /SYNC signal and the digital filter does not reset, you should be able to change the mode on the fly and wait 76-78 /DRDY pulses as the FIR filter clears out. 

    -Tony