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MSP430F6779A: MCU System hang-up and not reset by watchdog after ESD

TinK
Intellectual 815 points

Part Number: MSP430F6779A

I face problem about MCU System hang-up and not reset by watchdog after ESD (VDSYS becomes 2.5v instead of 3.3v ).

It returns to normal only after a power cycle. (Remove/replace power sources such as batteries, DC power supplies)

How can software solve this problem?

- Always enable watchdog

- Using a watchdog clock source with an internal VLO (should be more reliable than a crystal that might fail from ESD)

Is there anything else that can be done?

  • 0
    TI__Mastermind 27250 points

    Hi Tink,

    If the MCU is really hanging then I do not think this could be solvable by software. If the CPU isn't executing code it won't execute any software fix. You can do a software version of a watchdog using a normal timer then call a software BOR event. This will execute a higher level of reset than the watchdog, which may help give the same effect as removing power.

    I would generally recommend using the dedicated watchdog timer as the purpose is to reset the device. If you utilize one of the internal system clocks then the Clock-fail safe operation will switch to the VLO clock if the SMCLK or ACLK fails. 

    Another option is to use an external watchdog to reset the device using the reset pin.

    Regards,
    Luke

  • 0 in reply to Luke Ledbetter
    Intellectual 815 points

    Hi Luke,

    In case the MCU really hangs up, the Watchdog module hangs up too, right?

    I have added the software watchdog using timer to make BOR and Enable the reset pin, after trial with High level of ESD the system still hangs up (the reset pin also not response).  the power cycle only to recover the system.

    That means in this state the MCU and internal modules do not work. (Everything hangs up, right?)

  • 0 in reply to TinK
    TI__Mastermind 27250 points

    Hi Tink,

    Is the state easily repeatable? I would be curious to validate the MCU state, set a timer to toggle an available GPIO and see if the GPIO stops toggling when impacted by your ESD state. 

    You may also need to set the watchdog to interrupt mode then use a software BOR to reset the device to a higher state. But if none of the modules are working then you would need an external watchdog to manually toggle the reset line.

    Regards,

    Luke 

  • 0 in reply to Luke Ledbetter
    Intellectual 815 points

    Hi Luke 

    Yes, this can be easily replicated by using high levels of ESD on the circuit conductors. (But I think that rarely happens in the field).

    I have tested with a timer to switch GPIO but the result is freeze. (seem none of the modules work)

  • 0 in reply to TinK
    TI__Mastermind 27250 points

    Hi Tink,

    Since this is an ESD effect I do not think you would be able to implement a SW fix without the watchdog. There are many different hardware design considerations that can be utilized to protect against ESD including the enclosure that the device is in.

    MSP430 System Level ESD Considerations section 2.4.2 goes over some Software Considerations.

    Regards,
    Luke

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