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Thread: Issue powering Teensy 3.6

  1. #1

    Issue powering Teensy 3.6

    I have used a Teensy 3.6 to build a DIY eurorack sound module. I have a curious issue with power where sometimes the module will just not start up (say 1 in 3). This never happens if I power it via USB or a 5v DC wall plug, only when in my modular rack using my eurorack power circuit (shown below). I've tried this in multiple rack cases, with this as the only module. Has anyone else had problems of this nature? Is there a particularly large current draw from the 3.6 on start-up (card reader?). I've tried multiple voltage regulators (rated >100mA, like the 7805), but the result is the same. When it does power up, according to my bench supply, it's only drawing around 60-70mA.

    Even when the board doesn't startup, if I measure the voltage across the Teensy power pins, it correctly reads 5V.

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  2. #2
    Member+ Theremingenieur's Avatar
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    That happens if the 5V come up too slowly, most probably because of the 12V of the rack already taking too much time to rise. The professional way to solve that issue is using a better 12V to 5V regulator IC which has an additional “power good” pin which, when connected to the reset pin of the Teensy, will keep the signal low until the 5V are there and stable before driving the reset high and allow the Teensy to start. A cheaper solution would be a fixed boot delay by putting a capacitor between the reset pin and GND which would, together with the reset pin’s internal pull up resistor, delay the Teensy start, hopefully long enough for the power supply to have settled.

  3. #3
    That makes sense, thanks very much! What state is the Teensy in when this happens? Resetting the Teensy (via the on-board button) makes no difference once in this state, the power must be cycled.

  4. #4
    Member+ Theremingenieur's Avatar
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    The on board knob is NOT a reset knob, but a program knob which puts the Teensy in boot loader mode (which seems to be unresponsive, too).
    When this slow powering up happens, the Teensy will be in an undefined state, since some code has perhaps begun to run while some internal subsystems weren’t ready or vice versus.

  5. #5
    I see, thanks for the help! Is this issue documented somewhere? I would have thought it would be quite common.

  6. #6
    Senior Member manitou's Avatar
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    Quote Originally Posted by unicornpower View Post
    I see, thanks for the help! Is this issue documented somewhere? I would have thought it would be quite common.
    Similar discussions at
    https://forum.pjrc.com/threads/48082-3-5-Boot-Lockup
    https://forum.pjrc.com/threads/23647...Teensy-3/page2

  7. #7
    Member+ Theremingenieur's Avatar
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    For experienced circuit designers and debuggers, it’s the most normal thing to check the ramping up of the supply voltages with an oscilloscope first... And there are already around 4711 threads in these forums for this “issue”.

  8. #8
    Quote Originally Posted by Theremingenieur View Post
    For experienced circuit designers and debuggers, it’s the most normal thing to check the ramping up of the supply voltages with an oscilloscope first... And there are already around 4711 threads in these forums for this “issue”.
    Ah yes, I obviously didn't search very well Cheers for the assistance anyways..

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