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TPS659037: Watchdog reset duration

Part Number: TPS659037

PMIC team,

Our customer is working with the TPS659037, and is experiencing a problem that stems from the fact the reset duration is about 60 ms.  It's not long enough for all the rails in the system to discharge enough to reset the whole system.

Is there any way to extend the duration of the watchdog reset?

Thanks,
Darren

  • Hi Darren,

    I don't see any configurable options to mask turn on events after the watchdog power off event is complete.

    Would addition of a pulldown resistor (in addition to existing PMIC pulldowns) work to solve the issue on customer board? Alternatively, something that delays the power on request?
  • Hi Darren,

    When you say the rails do not discharge, do you mean PMIC rails or non-PMIC rails?  I would expect all the PMIC rails to discharge completely in 60ms, since all outputs have discharge resistors when the PMIC is disabled.  If your issue is with the PMIC rails, I'd like to understand better the capacitance on the rail, and at what rate it is discharging.  If your issue is with non-PMIC outputs, then I have some other suggestions below.

    In OTP, watchdog expiration is defined to generate a cold reset, per the SWOFF_COLDRST.WDT bit.  This means that when the watchdog expires, the PMIC will reset, and then automatically start up again after a fixed ~55ms delay.  The PMIC doesn't need an ON request to start up again after a cold reset event.

    I think there are two ways to keep the PMIC off for a longer time after a watchdog timeout:

    1. Write SWOFF_COLDRST.WDT=0 to cause a watchdog timeout to generate a shutdown event instead of a cold reset event.  Then you need to make sure there are no ON requests like PWRON=low or POWERHOLD=high - the PMIC will remain off until this on request happens.
    2. After the watchdog expires, create an "on request gating condition" in the system like RESET_IN=low.  Even if WDT is configured as cold reset, RESET_IN=low will keep the PMIC off until the next ON request.  The challenge here might be for the system to know when the watchdog expires so it can set RESET_IN=low.

    Regards,
    Karl

  • Thank you Kevin and Karl.

    Karl, one of your solutions may work.  I'll check with the customer.  The rails are from LDOs after PMIC.  I can't give much more detail without getting into specifics of the customer's design.

    Best regards,

    Darren