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UCC2946: The relation between RESET/WDI and WDO

user4979989
Intellectual 2800 points
Part Number: UCC2946

Hi team,

My customer is asking about datasheet figure 4 (Watchdog Circuit Timings)

1. Once RESET is low, WDO will always keep high no matter WDI pulse exceeds TWP or not?

2. If Q#1 is yes, once RESET is low so WDO is always high, if during that moment the WDI exceeds the TWP which indicates the system is abnormal, but the WDO is still high due to RESET is low, do we have any suggestions about this?

Thank you.

Regards,

Allen

  • 0
    TI__Mastermind 29900 points

    Hi Allen,

    1. If Reset/ is low, then on the next clock cycle, WDO/ will be set(or kept high), regardless of any other inputs or outputs.
    2. Your thinking is correct. The way we have the logic setup is that Reset/ takes priority over WDO/. This device cannot perform the function that you are interested in achieving, but I would think putting the system in Reset/ would signal abnormal operation that is being trying to be solved? Wouldn't resetting the system be the next step for the watchdog timer expiring?

  • 0 in reply to Marshall_Beck
    TI__Intellectual 2800 points

    Hi Marshall,

    For question #1, could you review if my understanding is correct?

    RESET pin is low from t9, so from t8 to t9 the duration is not count into TWP because watchdog is reinitiated in t9.

    If from t9 to t11, the WDI duration exceeds TWP, the WDO will be low.

    If from t9 to t11, the WDI duration doesn't exceed TWP, the WDO will still keep high.

    For question #2, do you mean let customer use RESET pin to alert their system is facing an abnormal condition?

    Because customer's original plan is to use the watchdog timer and RESET/ pin function independently, but seems the RESET will affect watchdog timer, I'll check with customer to discuss about the design.

    Thank you.

    Regards,

    Allen

  • 0 in reply to user4979989
    TI__Mastermind 29900 points
    Q1: RESET pin is low from t9, so from t8 to t9 the duration is not count into TWP because watchdog is reinitiated in t9.
    Marshall: I revised my earlier post to make my reasoning more concise on relatioship between Reset/ and WDO/.
    Q2: If from t9 to t11, the WDI duration exceeds TWP, the WDO will be low.
    Marshall: WDO/ will be low if Reset/ is high and a valid WDI has not been received (TWP has elapsed). WDI is ignored if Reset/ is low.
    Q3: If from t9 to t11, the WDI duration doesn't exceed TWP, the WDO will still keep high.
    Marshall: For this case, the diagram makes sense. WDO/ will remain high.
    Q4: For question #2, do you mean let customer use RESET pin to alert their system is facing an abnormal condition?
    Marshall: I think you are on the right track trying to gain a deeper understanding for system's need. Let me know what you find out.