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TPS3820 -50 Watchdog Control

Janaki Singotam
Prodigy 20 points
Other Parts Discussed in Thread: TPS3820

We are using the "TPS3820 -50" in our modified ECU design to control the watchdog. This ECU is having the Freescale's "S12XEQ384" micro controller.

From this micro controller we are connecting the "PT7/PWM7" pin to the "WDI" (PIN-4) of the TPS3820 chip.

I would like to understand how to control the watch dog using the this pin ?

What is the pulse rate i need to generate to feed the WDI to stop the RESET ?

  • 0
    TI__Mastermind 36110 points

    The datasheet's timing diagram provides some of the data you need.  It shows that you must toggle the WDI input continuously to keep the /RESET signal from going active.   If the WDI signal is not toggled within tt(out), /RESET goes low.  The tt(out) values for the different ICs are specified in the Switching Characteristics table.  The Timing Requirements tables shows that your WDI signal must have pulse widths greater than 100ns.

  • 0 in reply to Matthew Day
    Prodigy 20 points

    Hello Michael:

    Thank you for your quick response.

    I have a one more question,

    What is the behaviour of RESET ouput when i toggle the port PIN ON and OFF for every 10ms then wait in ON state for 50ms and repeat the tollgle with these kind of un-even togglings within 100ms to 300ms (or 50ms low and then toglle).  Please see the below image just for quick reference.

        

     

  • 0 in reply to Janaki Singotam
    TI__Mastermind 36110 points

    As long as you toggle the WDI low to high or high to low within the Ttout time specified in the datasheet, the TPS3820 will operate properly without generating an active low /RESET signal.  If you wait longer than Ttout, the /RESET output will go low.