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Microcontroller pins sticking high or low

Discussion in 'Microcontrollers, Programming and IoT' started by eem2am, Jul 7, 2010.

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  1. eem2am

    eem2am

    414
    0
    Aug 3, 2009
    We are doing low power SMPS’s with microcontrollers supplying the PWM to the FETs.

    Switching frequency = 100KHz.

    The problem is that micrcontrollers often experience a “stuck pin”, where a PWM pin sticks low or high.

    Obviously the watchdog will catch this, but if a pin gets “stuck high”, then the FET will be stuck ON and we will experience an overcurrent which will blow up the FET before the watchdog can respond.

    Do you have any stock circuits that can detect a “stuck high” PWM pin and pull it low?
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,305
    2,738
    Jan 21, 2010
    The solution is to create a hardware watchdog

    [​IMG]

    Sorry about the messy drawing :)

    Brief +ve going pulses will be transferred faithfully to the output. If the output is latched high, after an RC delay, the inverter output goes low and the output is also pulled low.

    The rc delay should be longer than the maximum time the output should remain turned on, but lower than the time it takes to fry the mosfet.

    You could make it this way with single gate SMD components, or pick (say) a quad schmitt trigger NAND gate (74HC132) and build the equivalent circuit.
     

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