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ADS5294: Need to use SYNC across multiple devices when NOT decimating.

Robert Servilio19
Prodigy 180 points
Part Number: ADS5294

Our system consists of ADS5294s across 4 different modules that can be powered up and programmed separately as the system is brought up.

However, once the sampling process starts, we are under the impression that as long as there is no decimation, and assuming that the sample clocks and input signals applied to each ADC are coherent, we should NOT require the use of the SYNC input to synchronize the 4 ADCs.

What we see is that the outputs (looking across all the ADCs) can be off by a sample (sampling at 20MHz or 40MHz).

We then modified our system to allow for a SYNC to be applied to all ADCs simultaneously and when we encountered this one sample skew, applied the SYNC and found the resulting data to now become aligned.

We were surprised by this as the SYNC descriptions in the data sheet and any forums I've read only apply to requiring SYNC for decimation.  So my question is: are there any other situations where SYNC should be used and does the scenario we encountered above make sense?

Thanks,

Bob

  • 0
    TI__Genius 12025 points

    Hi Bob,

    How are you?

    Thank you for using TI ADS5294 devices.

    We will look into your question and reply back to you very soon.

    Thank you again!

    Best regards,

    Chen

  • 0 in reply to Chen Kung
    TI__Genius 12025 points
    Hi Bob,

    Yes, we recommend using SYNC input signal to align
    all the ADC output data (from one device to the other device).

    One good advantage is:
    Since input clock signal is running in continuous mode,
    using SYNC signal pulse can help us understand which Sample
    (digital output signal, such as Sample Number 1) we just captured
    right after the SYNC pulse was started.

    Also SYNC pin can be used to re-align timing
    across multiple ADS5294 chips again,
    when SYNC pin (rising edge) is enabled.

    So that is recommended to use SYNC signal
    when multiple ADS5294 devices are used on the same board.
    Also please keep the input clock needed to be routed with identical length
    to all the ADS5294 devices. This is important for the input clock timing.

    Thank you very much for using ADS5294 devices.

    Best regards,
    Chen
  • 0 in reply to Chen Kung
    Prodigy 180 points

    Thanks, Chen.

    I just want to be sure that your response applies to multiple devices in normal 1:1 sampling mode (i.e., WITHOUT DECIMATION).  Correct?

    Also, can you explain what timing is re-aligned by the SYNC, as you explained above?  The only timing the user supplies is the sample clock, correct?  Are there other internal counters, state machines, etc., that are initialized by SYNC even when in non-decimation mode?

    Does TI recommend that we re-issue SYNC regularly, or always after power-up, or when changing sample rates or other parameters?

    We are trying to understand the mechanism so that we move forward with our development and testing correctly.

    Thanks again.

    Bob

  • 0 in reply to Robert Servilio19
    TI__Genius 12025 points
    Hi Bob,

    First, you are correct.
    Without decimation, we still can apply SYNC pulse.

    When SYNC pulse is used, ADS5294 will make an internal synchronization signal.
    This signal will reset (re-align) the ADC sample clock internal signal for each device
    (each channel as well)
    (note: also please make sure these multiple devices share the identical input clock.).

    SYNC pulse must be applied after power-up and registers have been set.
    Also there is no need to re-issue SYNC pulse
    unless the power is turned-off and turned-back-on
    or the register settings are changed.

    Thank you very much!
    Have a nice day!

    Best regards,
    Chen
  • 0 in reply to Chen Kung
    Prodigy 180 points

    Hello Chen,

    Thanks for the timely responses.

    Regards,

    Bob