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ADC12J4000 - SYSREF processing

Hiroshi Katsunaga
Mastermind 6480 points
Other Parts Discussed in Thread: ADC12J4000, LMK04828

Hello,

My customer have some questions about SYSREF processing for ADC12J4000.

[Q1]

Is my understanding correct ?

<My understanding>

In case of Periodic (Continuous) SYSREF, the JESD204B synchronization process is carried out in the first SYSREF rising edge.

When synchronization is established, the subsequent edges are ignored.

[Q2]

In case of Periodic SYSREF, why must the SYSREF processing in the ADC be disabled before the ADC SYSREF is turned off at the LMK04828 ?

If the SYSREF processing remains an enable when SYSREF is turned off,  What kind of risk is there ?

This question is related to previous my thread (ADC12J4000 - Your recommendation for SYSREF type).

[Q3]

In case of DC coupled SYSREF, why does the ADC not need to disable SYSREF processing ?

In this case, is there any risk ?

This question is related to previous my thread (ADC12J4000 - Your recommendation for SYSREF type).

These questions are caused by our understanding of SYSREF processing for ADC12J4000 being in sufficient.

I want to know the detail for the SYSREF processing. 

Please help us !

Best Regards,

Hiroshi Katsunaga

  • 0
    TI__Mastermind 44680 points

    HI Hiroshi

    Regarding the latest questions.

    Q1) Yes, as long as the subsequent edges have the proper alignment with respect to the initial edge they are ignored.

    Q2) If the SYSREF is DC coupled, and can be turned off with a logic 1 or 0, then SYSREF processing does not need to be disabled.

    If SYSREF is AC coupled, the signal at the ADC SYSREF inputs will float to an indeterminate differential state (SYSREF+ = SYSREF-). Any noise on the lines may cause the SYSREF receive to toggle.  In this case the ADC SYSREF processing must be disabled before the SYSREF source is turned off.

    Q3) As noted in Q2, as long as a defined logic level can be set on SYSREF when it is disabled, then SYSREF processing does not need to be disabled. These is no risk to keeping SYSREF processing enabled as long as there will not be any 0->1 transitions on the SYSREF input.

    I hope this is helpful.

    Best regards,

    Jim B

  • 0 in reply to Jim Brinkhurst1
    Mastermind 6480 points
    Hi Jim,

    Thank you for your fast response.
    I understood your all comments.

    Your comments are very clear and this is very helpful for us.

    Thank you for your cooperation !

    Best Regards,
    Hiroshi Katsunaga