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Disabling the TPS3813I50 Watchdog Timer

Marcos Soriano
Prodigy 40 points

Hello Folks!

  1.  I've read the SLVA145 Application Notes on Disabling the Watchdog Timer. Will keeping the WDI pin of the TPS3813I50 open will also allow for  disabling its watchdog timer. There were several Supervisory ICs cited in SLVA145 but I did not see any reference to TPS3813I50 IC.

  2. if SLVA145 Application Notes is applicable to TPS3813I50, will there be any performance/design issue if I opt to use a CMOS Analog Switch (i.e., NLAST4599) instead of SN74LVC1G126DCK 3-state buffer shown in the application example in SLVA145? 

Rgds,

Marcos

  • 0
    TI__Expert 3910 points

    Hi Marcos,

    The application described on SLVA145 is not applicable to TPS3813I50 because as described in the datasheet, WDI must be driven at all times and might not be left floating. 

    Regards,
    Victor

  • 0 in reply to Victor Salomon
    Prodigy 40 points
    Hi Victor,

    So what is TI's recommendation on how to disable TPS3813I50 Watchdog Timer so that it does not trigger a reset? My application requires that this WDG IC be disabled while the blank Microcontroller of the ECU is Flash-programmed for the first time.

    Hope you and the good people at TI have some suggestions on this matter.

    Rgds,
    Marcos
  • 0 in reply to Marcos Soriano
    TI__Expert 3910 points

    Hi Marcos,

    WDI cannot be disabled on TPS3813I50, however depending on your application's constraints you might be able to program the upper boundary. Using the following equation (1) from the datasheet you can calculate which CWP you can use depending on your flashing timing. Consider the figure below extracted from the datasheet:

    Given equation (1): twindow,typ = (CWP/15.55pF + 1) * 6.25 ms, and keeping in mind the that the maximum external capacitor you can use is 63 nF, you can have up to a twindow,typ of 25.32 seconds, or twindow,min = 18.99 seconds (for more details refer to page 9 of the datasheet)

    This might be helpful because as described in the datasheet, "After the reset of the supervisor is released, the lower boundary of the first WDI window is disabled.", providing you with that window time to perform your operation. 

    Best Regards,
    Victor

  • 0 in reply to Victor Salomon
    Prodigy 40 points

    Hi Victor,

    From your example using the 63nF cap, that Flash-programming operation of my ECU's Microcontroller be completed under 18.99s, once reset of TP3813I50 is released. Is my understanding correct?

    Thanks for your patience in replying to my queries!

    Best Rgds,

    Marcos

  • 0 in reply to Marcos Soriano
    TI__Expert 3910 points
    Hi Marcos,

    Yes, the flash-programming operation of your ECU's micro-controller should be completed under 18.99s after /RESET is released and start pulsing WDI, otherwise if WDI receives no pulse during this amount of time /RESET will be asserted.

    Regards,
    Victor