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TPS3305: TPS3305-33DGN - How to disable by CPU

Edmond Ng
Prodigy 20 points
Part Number: TPS3305
Other Parts Discussed in Thread: TPS3850

Dear all,

I read multiple threads

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/375608/tps3305-questions?tisearch=e2e-sitesearch&keymatch=TPS3305#

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/88598/tps3305-wdi-function?tisearch=e2e-sitesearch&keymatch=TPS3305#

that mentioned the TPS3305-33DGN watchdog WDI can be disabled by leaving it to float. However this defeats the purpose of using this chip because if I do not need a watchdog would have got a power management reset chip without the watchdog. If i connect the WDI to a CPU, how can I enable or disable the watchdog WDI? My understanding is that I have about 1.6s to start the waveform generator or the watchdog kicks in. With an older CPU, the init time is much slower so I will need control of the time to enable/disable watchdog, ideally to enable watchdog after our device boots up initialization.

What is the correct method or circuitry I should be considering to enable and disable watchdog of TPS3305 with control from micro?

Thanks

  • 0
    TI__Mastermind 44965 points

    Hi Edmond,

    I don't believe that floating the WDI pin will disable the watchdog timer.  Here are a few questions for you:

    1. Are you looking for a supervisor + watchdog for your application or just a supervisor? 

    2. Are you looking for a multichannel supervisor?

    3. Can you tell me more about your application so I can assist you in finding the right part for the application?

    If you are looking for supervisor + watchdog where you can have the option to turn off the supervisor, I would suggest the TPS3850/51/52.  These parts have a pin(s) to allow you to disable the watchdog timer.

    Ben

  • 0
    Prodigy 20 points

    HI Ben,

    Thank you for the response. TPS3305 is currently designed into our CPU board. What I need is a 3.3V, 5V supervisor, push button input reset and external watchdog. The TPS3305 appears to be the perfect choice because it has all three options I need, except the watchdog which appears to not have the ability to be enabled/disabled. Am I understanding correctly that there is no way to disable TPS3305 even if it is tied to a micro pin?

    Thanks

  • +1 in reply to Edmond Ng
    TI__Mastermind 44965 points

    Hi Edmond,

    After digging around I did find this application report saying that if the WDI pin is left floating, the watchdog can be disabled.

    https://www.ti.com/lit/an/slva145/slva145.pdf

    One way to disable the watchdog is to place an NMOS device in series with the CPU and TPS3305.  The gate of the NMOS can be switched off to disable the watchdog or switched on to enable the watchdog.

    Ben

  • 0 in reply to Ben C
    Prodigy 20 points

    Thank you Ben, it works for disabling it,

  • 0 in reply to Edmond Ng
    TI__Mastermind 44965 points

    Hi Edmond,

    Thank you for letting me know that your application is working!  Good luck to you and have a great weekend!

    Ben