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Thread: Teensy 4.0 hardware / schematic question

  1. #1

    Teensy 4.0 hardware / schematic question

    Hi - can someone please tell em the purpose of the P-channel MOSFET shown below? To me it looks as though the gate is permanently tied to GND which would mean the MOSFET is always allowing current to flow through the source-drain channel to supply the 3.3v regulator. Why is this MOSFET required at all?

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    Second question, does anyone know the part number for the momentary push button switch used on the Teensy 4.0? Is it the PTS810? https://au.mouser.com/Search/Refine?Keyword=pts810

  2. #2
    Senior Member+ defragster's Avatar
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    this question came up and was answered yesterday.

    IIRC in this mode as noted in that post - it acts as a simple diode with a lower voltage drop that a diode would.

    Paul has listed the button part before on forum - not sure if it might be in any OSH board BOM and easier to find there short of an update.

  3. #3
    Quote Originally Posted by defragster View Post
    this question came up and was answered yesterday.

    IIRC in this mode as noted in that post - it acts as a simple diode with a lower voltage drop that a diode would.
    Thanks - found it in search results

  4. #4
    While I'm on the schematics, where is this diode connected to? It's floating in the current schematic? Is it just paralleled for current handling?

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  5. #5
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    Quote Originally Posted by ilium007 View Post
    While I'm on the schematics, where is this diode connected to? It's floating in the current schematic? Is it just paralleled for current handling?

    Click image for larger version. 

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    Paralleled diodes is a big no-no - I assume it is connected to a pad or unused

  6. #6
    Senior Member PaulStoffregen's Avatar
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    That extra diode is unused. It really is unconnected, as the schematic shows.

    The BAT54C comes with 2 diodes inside 1 package. The design needs 3 diodes. It's one of those strange quirks of modern semiconductors where 4 diodes (as 2 dual diodes parts) are smaller and less expansive than using the required 3 diodes. So 4 are in the design the 4th is simply left unused.

  7. #7
    Quote Originally Posted by PaulStoffregen View Post
    That extra diode is unused. It really is unconnected, as the schematic shows.

    The BAT54C comes with 2 diodes inside 1 package. The design needs 3 diodes. It's one of those strange quirks of modern semiconductors where 4 diodes (as 2 dual diodes parts) are smaller and less expansive than using the required 3 diodes. So 4 are in the design the 4th is simply left unused.
    Thanks Paul - learning more every day!

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