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Thread: Teensy 3.2 Schematics Questions

  1. #1
    Junior Member
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    Teensy 3.2 Schematics Questions

    Hello,

    I have recently been trying to design a custom Teensy board for my project. I've been basing it off of the Teensy 3.2 schematics, but I have a bunch of (possibly dumb) questions.

    First, why was a voltage regulator added to the teensy 3.2? It seems like the MK20DX256VLH7 already had a usb voltage regulator pin (VREGIN), and that was what was used on the teensy 3.1. Second, why are the three VDD and the VOUT33 pins all connected together in the schematic?

    While looking for more info on the schematics, I found this thread. A little ways down, a user named Constantin replied with an attached image of a schematic displaying how to get the MK20 (from their eagle cad library) working. In the image, they connected the VCC pins, the VOUT33, but also the VREGIN. Is this intentional, or could it be a mistake? (I presume this is where I am expected to hook up the usb power if I were to use this schematic.)

    Lastly, (probably the worst question lol,) what are the 2 rectangles at the top left of the schematic..........?

    This is probably longer than it needs to be..
    Thanks for any help!

  2. #2
    Senior Member PaulStoffregen's Avatar
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    Quick answers, except I'm not going to comment on Constantin's schematic - only answering regarding the PJRC schematic.


    Quote Originally Posted by Pancake View Post
    First, why was a voltage regulator added to the teensy 3.2? It seems like the MK20DX256VLH7 already had a usb voltage regulator pin (VREGIN), and that was what was used on the teensy 3.1.
    Mainly because the on-chip regulator was unable to power wifi boards, at first CC3000 around the Teensy 3.1 -> 3.2 transition, then later ESP became popular.

    There were also a number of people who damaged their Teensy 3.0 & 3.1 boards by applying over 5.5V, sometimes with 5V power supplies having terrible startup behavior. A decision was made to go with a regulator capable higher voltage. Perhaps it was unnecessary overkill, maybe the decision involved more emotion than critical engineering and business logic, but after what I will admit may have been only a relatively small number of particularly painful incidents, we wanted a regulator capable of withstanding "abuse".


    Second, why are the three VDD and the VOUT33 pins all connected together in the schematic?
    The on-chip USB transceiver is powered from the VOUT33 pin. Yes, it says "OUT" but power must flow into the pin for USB to work if the on-chip regulator isn't used. It's a detail buried deep in the chip's documentation...


    Lastly, (probably the worst question lol,) what are the 2 rectangles at the top left of the schematic..........?
    Those are the pads on the bottom side which you would cut apart if you want to externally apply 5V power and avoid it flowing back to the USB cable.

  3. #3
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    Thanks for the quick and concise reply! That really clears things up a lot. (Especially the VOUT33 thing.)

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