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Thread: Powering Teensy 3.2 from 3v3

  1. #1
    Junior Member
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    Powering Teensy 3.2 from 3v3

    Hello again! My project is coming along delightfully, and it's time for me to order some testbed pcbs to get some real performance tests done. I'm using a LM1117MPX-3.3 to get a 3v3 source off of my +12 rail. This is the primary source I've been using for things like my DAC, but in testing, I've been powering the Teensy from the USB connection.

    Now that I'm looking to move things off a bit, I'd like to know if it's possible to drive the Teensy with a 3v3 line, or if I'll need to put in a LM1117MPX-5.0 in there. Not the end of the world if I need to, but added part count is just something I'd like to consider. I'm aware that there would be issues driving it from external USB while it's powered by the test board, but I've dealt with those in the past ala x-acto knives and diodes and such.

    Thanks!

  2. #2
    Yes, you can feed the output of a 3.3V regulator into the Teensy (use one of the 3V3 pins). You'll want to cut the trace on the back of the board if you plan to connect USB while the 3.3V supply is connected, but you seem to be aware of that.

  3. #3
    Senior Member PaulStoffregen's Avatar
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    Power from 3.3V is fine. Just be *really* careful with that 12V line! The most common cause of dead Teensy boards is loose wiring with this sort of circuit. The slightest moment of 12V touching the 3.3V power line will instantly kill a Teensy.

    Also consider LDO chips like LM1117 need a capacitor located very close to their output & ground pins. Without the cap, or if it's too far away, those regulators are unstable.

  4. #4
    Member gimpo's Avatar
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    (Thread resurrection )
    I plan to power a Teensy 3.2 by using the 3v3 pin too.

    Question:
    do I need to cut the "VUSB trace" if reprogramming Teensy with the USB cable and the supply line (going to the 3v3 pin) temporary disconnected?

    I'm in the test-phase of my software. This means that I need to repeat the steps below many times:

    1. detach the Teensy from my motorcycle parked in garage
    2. go to home and make my changes to the software, by powering it only via the USB cable
    3. return to the garage and re-connect the Teensy back.

    (When connected to the motorcyle, the Teensy is powered by the 12V battery, via a 3,3V Murata regulator.)

    I read somewhere that if I don't cut the trace, then I could have some problems. The current could flow through the standard voltage regulator from the 3V3 pin, causing some damages. Is this true?

  5. #5
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    The problem with not cutting VUSB trace is that you could damage your PC *if* you keep the 3.3V power source while you plug the USB.
    So, in your case (3.3V power source in the garage :-) ) you could avoid cutting the trace.
    Still, it's a recommended thing to do, just in case.

  6. #6
    Member gimpo's Avatar
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    Ok. Thanks for the answer
    So the "risk" occurs only when the the USB connector and the external 3.3V supply line are both plugged at the same time.

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