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SAM3N00B micro repeated reset = OK?

Discussion in 'Microcontrollers, Programming and IoT' started by eem2am, Apr 27, 2013.

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  1. eem2am

    eem2am

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    Aug 3, 2009
    Hello,

    We are using a SAM3N00B microcontroller in our "special" emergency light application.

    Whenever the battery is removed when the mains is ON, the microcontroller repeatedly powers down and powers back up again.......(once every 5 seconds)

    Is this a problem? (does repeated power up and down damage the micro?)

    Our new software engineer says it is a problem, but can't say why.


    Its certainly not a problem from the point of view of the operation of the unit.

    SAM3N00B datasheet
    http://www.atmel.com/Images/doc11011.pdf
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Power cycling doesn't harm the µC - normally.
    However, as long as there is mains supply, the µC should not power down. Supplying the µC is the main task of a power supply. Even without a battery. Therefore you should locate the source of the power cycling (e.g. bad voltage regulator, bad capacitors, incorrectly wired watchdog etc.) and eliminate it.
     
  3. eem2am

    eem2am

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    Aug 3, 2009
    when the battery is removed, the micro gets powered by our resonant inductive coupler.....this raises the battery rail to >8.5V, which also means overvoltaged battery, so we have to get the micro to shut off the coupler when battery rail >8,5V....but then if the battery has been removed we end up constantly power cycling the micro.
     
  4. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
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    Nov 28, 2011
    As an embedded systems designer and programmer, I would consider a situation where the microcontroller is repeatedly powered up and powered down to be a major issue. Certainly it won't damage the microcontroller but that kind of behaviour is totally unacceptable in an embedded system.

    It seems like you need to fix whatever it is that causes the battery voltage to exceed 8.5V when the circuit is running from the inductive coupler with the battery removed.
     
  5. eem2am

    eem2am

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    Aug 3, 2009
    The R.I.C. is basically a current source, and its expensive to stop the above behaviour.
    The emergency unit is useless without a battery, so its operation without the battery is not that crucial to control.
    As long as constantly resetting/powering up and down does not harm the micro, then its ok.
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Or turn it into a feature with the power to the uC lighting a "power" LED. If you take the battery out it will flash to warn you of the situation!

    Something about lemons and lemonade :)
     
  7. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    You're trying to fix a secondary effect (power cycling) whereas the primary effect (overvoltage) goes unhandled. You should go about it the other way.

    What's expensive about a small voltage regulator or a plain zener diode? A zener diode might work without a series resistor if your power circuit really behaves like a current source.
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    I agree 100%. I hope that if you're using something to limit the voltage if you have a power supply like the one I think you're describing.

    I was assuming that the voltage rises slightly above 8.5V. If it is actually rising far higher (to the point of approaching or exceeding exceeding absolute maximum ratings) then you absolutely need to fix that first so that your design is safe and reliable.
     
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