APX809

Discussion in 'UDOO NEO' started by 1chi, Mar 29, 2017.

  1. 1chi

    1chi New Member

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    Hi everybody,

    I have a little problem with the UDOO Neo power supply.
    I power the UDOO using the 12V Jack.
    I have several devices attached to the 5V output (2x GPS, IMU, Barometer, 2x 9gr Servo, Lidar)

    When I try to power the board I hear a periodic clicking and the board does not power. Looking in the UDOO schematics, I decided to remove the APX809. The board boots and everything seems to work fine.

    Could somebody please explain the purpose of the APX809 to me?
    What are the risks of removing it?
    BR,
    1chi
     
  2. sirrab

    sirrab UDOOer

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    It is a reset IC for the micro. The micro could not power up properly. You are better off fixing the power issue.
     
  3. jas-mx

    jas-mx Active Member

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    The 5V rail comes via a AP3503F which rated to 3A so removing the APX809 you risk damaging the AP3503F. Ideally you should be powering all your devices from a separate 5V source.
     
  4. 1chi

    1chi New Member

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    Thank you for the replies, however, I still don't see how something else could be damaged :D

    Fixing the power issue (e.g. with a different supply) is unfortunately no option for the moment.
    @jas-mx How could the AP3503F be damaged? It has a build-in over current protection, so if more than 3A is drawn it should simply turn off.

    I'm running without the APX809 for a while now, and didn't run in into any problems yet.
    I attached some screenshots from VCC_SW(yellow) and VCC_SW_IN(green) during power up.

    Udoo Neo Regular:
    [​IMG]

    Udoo Neo with load:
    [​IMG]

    Udoo Neo without APX809
    [​IMG]
    [​IMG] [​IMG]
     
  5. jas-mx

    jas-mx Active Member

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    Yes your right it has over current protection, however speaking from experience (with a numerous dev boards) the DC-DC converters can be temperamental depending on the ambient temperature and load current.

    The benefit of the APX809 are :

    1. A reset only occurs if the supply voltage is at percentage of nominal. Haven't checked the imx6sx but most microprocessors reset between 5-10% nominal voltage. The APX809 ensure it only happens at a predefined percentage. This prevents indeterminate resets occurring between the 5-10% zone.
    2. The reset is held for a full 240ms to prevents brownout conditions.
     
    Last edited: Apr 14, 2017

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