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TPS3852: WahctDog circuit "TPS3851H33EDRBR" change to "TPS3852H33DRBT" question.

Eason Lu1
Prodigy 40 points
Part Number: TPS3852

Hi Teams,

Below is our currently WahctDog "TPS3851H33EDRBR" Circuit and Behavior:

- After ~56.68s no received the WDI single then Reset#/WDO# will go low to the EC25 module(RESET_N).

- Every 30s WDI send signal to reset watchdog timmer,(WDI signal about ~90us)

  so the WDO#/Reset# won't sent low signal to EC25 module(RESET_N).

If we replaced "TPS3851H33EDRBR" with "TPS3852H33DRBT"(Window watchdog timer).

is need to change HW or FW config for the Window watchdog lower /Upper boundary? please advise.

WDI signal timing

Thanks!

  • 0
    TI__Guru 56345 points

    Hi Eason,

    If the WDI signal continues to output every 30s, I believe you will need to change the CWD capacitor value.  The upper boundary equation is: 

    From the schematic, I see that CWD has a capacitor value of 0.68uF.  The upper boundary time is calculated to be:

    tWDU = 52.69 seconds

    tWDL = tWDU * 0.5 = 26.34 seconds. 

    The tWDL boundary value is very close to the WDI time of 30 seconds.

    If you change the CWD value to 0.51uF, the tWDU and tWDL values are:

    tWDU = 39.53 seconds

    tWDL = 19.76 seconds

    which makes the WDI time pretty much centered to the watchdog window.

    Ben

  • +1 in reply to Ben C
    TI__Guru 56345 points

    Hi Eason,

    Just following up with you if you have any other questions.  If not please close the thread by clicking on "resolved".  Thanks and have a good weekend!

    Ben