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Thread: Teensy 3 Power-On Reset

  1. #1
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    Teensy 3 Power-On Reset

    I'm using a Teensy 3 in combination with a 150W 5V switching PSU. When I power the Teensy from this 5V source, it doesn't do anything when switching on the PSU. It does work however when I first start up the PSU and then connect the Teensy's power.

    Does the Teensy have an internal Power-On Reset circuit that can be enabled? In the datasheet it is mentioned to have one. Or do I need an external POR?

    Thanks
    klaasdc
    Last edited by klaasdc; 01-22-2014 at 09:36 AM.

  2. #2
    Senior Member PaulStoffregen's Avatar
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    You could connect an external power-on-reset chip to the reset pin. On Teensy 3.0 it's easy to access. On Teensy 3.1, the reset pin was moved to a pad on the bottom side.

    Can you please post specific info about this power supply, like the make and model? Or a photo? Can I buy the same power supply somewhere online? I'd like to get one here to investigate this problem.

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    Quote Originally Posted by PaulStoffregen View Post
    You could connect an external power-on-reset chip to the reset pin. On Teensy 3.0 it's easy to access. On Teensy 3.1, the reset pin was moved to a pad on the bottom side.

    Can you please post specific info about this power supply, like the make and model? Or a photo? Can I buy the same power supply somewhere online? I'd like to get one here to investigate this problem.
    Yes, I got the power supply from here: http://www.ledsee.com/index.php/powe...pply-5v-detail

    I can try to find a manufacturer name when I'm back home.
    Last edited by klaasdc; 01-22-2014 at 11:50 AM.

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    Could it be that the 150W power supply's voltage ramp-up slope is too slow for the reset circuit in the Teensy to work properly?

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    Quote Originally Posted by stevech View Post
    Could it be that the 150W power supply's voltage ramp-up slope is too slow for the reset circuit in the Teensy to work properly?
    That is possible, but the POR circuit is supposed to keep the uC in reset until a high enough voltage V_lvdl of 1.6V is reached? The minimum supply voltage of the MK20DX128 is 1.71V according to the datasheet. That seems a little illogical...
    Anyway, can the 3.3V converter on the board be responsible too?

    The PSU brand seems to be CZCL, in China (ofc). I wired an USB cable to the power supply that plugs into the Teensy micro usb socket.

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    Looked at the voltage vs. time slope on a 'scope? Maybe the power supply wants a few hundred mA load to startup properly. You could put a low ohm resistor on and see what happens.

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    Quote Originally Posted by stevech View Post
    Looked at the voltage vs. time slope on a 'scope? Maybe the power supply wants a few hundred mA load to startup properly. You could put a low ohm resistor on and see what happens.
    The PSU also feeds 144 WS2812B LEDs and an USB Host Shield with Xbox controller attached, so there is definately some idle load.

    I suppose looking at it on a scope would be best, but I don't have one nearby so that will have to wait

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    Right. I presume the LEDs are not ON at power-up.

  9. #9
    Senior Member PaulStoffregen's Avatar
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    I have 4 power supplies here that look nearly identical. They were all cheap from no-name Chinese vendors. 3 are on the back side of the OctoWS2811 test board (which I've used for pretty much all development work on OctoWS2811), and another is on my shelf of spare stuff. I used all 4 many times without trouble.

    Obviously something really strange is going on with that particular supply. If I could just buy the same one somehow, I would. I'd really like to be able to test it here.

  10. #10
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    One item in spec says
    Rise,hold up time--------------------50mS,20mS at full load (typical)
    similar but not exactly the same:
    http://www.meanwell.com/search/S-150/S-150-spec.pdf

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