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Thread: Teensy 4.0 Power

  1. #1
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    Teensy 4.0 Power

    On the back side of the "Welcome to Teensy" card that accompanies the chip, there is text
    "Cut to separate VIN from VUSB if using battery or external power." Does this mean that
    the Teensy can be powered by external OR USB power? Are they mutually exclusive, or
    can one use either by cutting or not cutting the trace?

    Thanks,
    John-

  2. #2
    Senior Member+ MichaelMeissner's Avatar
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    Quote Originally Posted by jpicciri View Post
    On the back side of the "Welcome to Teensy" card that accompanies the chip, there is text
    "Cut to separate VIN from VUSB if using battery or external power." Does this mean that
    the Teensy can be powered by external OR USB power? Are they mutually exclusive, or
    can one use either by cutting or not cutting the trace?

    Thanks,
    John-
    Note, I am a software guy, if somebody who is a EE replies with a different answer, believe them.

    Unless you cut the trace, VIN and VUSB are connected together. So if you apply power to the VIN pin, it can be fed back to the USB connection if the VIN power is higher than the USB power. Some USB connections aren't prepared if you feed power back to them.

    If you cut the trace, then you must apply power to the VIN/Ground. The Teensy will not work if you just plug in the USB plug without applying power to the VIN pin. Note, the USB connection will not be used to power the Teensy.

    One use of cutting the the trace is to connect a lipo battery charger to VUSB and ground. Then you connect the power output from the charger to VIN on the Teensy (connect ground to both). If they charger has a battery connected, but no USB, then the battery will power the Teensy. Depending on the charger, if you connect a USB cable, the Teensy will either be powered by the battery or straight from the USB connection, and the battery will be re-charged from the USB power source.

    Another use is to provide an on/off switch to the Teensy, where you connect an on/off switch between VIN and VUSB.

  3. #3
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    Quote Originally Posted by MichaelMeissner View Post
    Note, I am a software guy, if somebody who is a EE replies with a different answer, believe them.

    Unless you cut the trace, VIN and VUSB are connected together. So if you apply power to the VIN pin, it can be fed back to the USB connection if the VIN power is higher than the USB power. Some USB connections aren't prepared if you feed power back to them.

    If you cut the trace, then you must apply power to the VIN/Ground. The Teensy will not work if you just plug in the USB plug without applying power to the VIN pin. Note, the USB connection will not be used to power the Teensy.

    One use of cutting the the trace is to connect a lipo battery charger to VUSB and ground. Then you connect the power output from the charger to VIN on the Teensy (connect ground to both). If they charger has a battery connected, but no USB, then the battery will power the Teensy. Depending on the charger, if you connect a USB cable, the Teensy will either be powered by the battery or straight from the USB connection, and the battery will be re-charged from the USB power source.

    Another use is to provide an on/off switch to the Teensy, where you connect an on/off switch between VIN and VUSB.
    ------------------------------------------

    Thanks, that pretty much answers my question.

    The reason I asked the question, is that I soldered the Teensy to a protoboard and then realized the trace was in place,
    however, I would only apply 5v to the Vin pin, so what I understand from your answer is that would be O.K. That is, leaving
    the trace in place and using the USB when 5v is applied to Vin on the Teensy wouldn't cause any problems to the USB or the Teensy.
    Do I have that right?

    Thanks,
    John-

  4. #4
    Senior Member+ defragster's Avatar
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    Quote Originally Posted by jpicciri View Post
    ------------------------------------------

    Thanks, that pretty much answers my question.

    The reason I asked the question, is that I soldered the Teensy to a protoboard and then realized the trace was in place,
    however, I would only apply 5v to the Vin pin, so what I understand from your answer is that would be O.K. That is, leaving
    the trace in place and using the USB when 5v is applied to Vin on the Teensy wouldn't cause any problems to the USB or the Teensy.
    Do I have that right?

    Thanks,
    John-
    ... not sure it reads that way ?

    If the trace is not cut - and some other power is applied to VIN - then USB should not be connected with power coming in over USB.

    If you have a cable you can cut the 5V line that would be okay, or some type of 'dongle' device that cuts the 5V from the USB but connects the data and GND, that would be okay.

  5. #5
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    O.K. Thanks. I thought it read that way because I assumed that applying a voltage over 5v to Vin would possibly damage the USB.
    I'll make amends.

    Thanks again,
    John-

  6. #6
    Senior Member+ defragster's Avatar
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    What is posted with regard to pushing higher voltage back to USB applies the other direction too - supplies wouldn't expect to be presented with a higher voltage and necessarily run well or safely.

    Also not an EE - but it seems two power supplies should never meet. General solution posted on PJRC.com shows Dual Diodes so the stronger supply gets held back so no current can push to the lower voltage.

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