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Thread: Teensy 3.0: 3.3V pins, maximal Current

  1. #1

    Question Teensy 3.0: 3.3V pins, maximal Current

    Hi!
    Just a small question.
    According to this diagramm are 3.3 V pins connected toghether.
    But on the small "Datasheet" shipped with my board is one pin* marked with (100 mA max), the other 2 not.
    Question: does this max current drainage apply for all of them?
    Or for the other two other values must be considered?

    Thanks

    Bye


    *: the pin is close to pin 23, left side.

  2. #2
    Senior Member PaulStoffregen's Avatar
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    Quote Originally Posted by dave View Post
    Question: does this max current drainage apply for all of them?
    TL;DR: Yes.

    When the Teensy3 gets 5 volt power, either from the USB, or from VIN (hopefully with the VIN-VUSB pads cut apart so current can't flow backwards up the USB cable and into the PC), the voltage regulator inside the MK20 chip creates the 3.3 volt power that runs everything.

    The regulator inside the chip is connected to the VREGIN and VOUT33 pins. The 100 mA guideline printed on the reference card is based on the regulator's 120 mA spec, and an assumption that the chips on Teensy3 use approx 20 mA, leaving about 100 mA capacity that you could use to power up external circuitry.

    If you tried to draw 100 mA from the 3.3V pin next to AGND and also 100 mA from the 3.3V pin on the right side of the board, and also another 100 mA from the 3.3V pad on the bottom side, that would total to 300 mA. Since the little on-chip regulator is only spec'd to 120 mA, you'd be far over its limit. I believe the regulator has an automatic shutdown if you exceed some high current. Usually those safety features aren't a precisely controlled value, so it can vary from chip to chip and with temperature and maybe other factors. It's probably best not to push it beyond 100 mA.

  3. #3
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    Quote Originally Posted by PaulStoffregen View Post
    The 100 mA guideline printed on the reference card is based on the regulator's 120 mA spec, . . .
    I have both the 3.1 K20 processor datasheet and reference manual and I don't see a max current spec for the USB regulator on any of their 1400 pages. Paul, where did you see it?

    Thanks!

  4. #4
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    Hi Paul,
    The ESP8266 spec sheet shows > 100mA while transmitting (135mA to 215mA depending on tx power)
    Any suggestions on how to power ESP8266 together with Teensy LC?

  5. #5
    Senior Member+ defragster's Avatar
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    Solutions I've seen give the ESP8266 its own regulated power for that reason. Those were on breadboard adapters or solo solutions, or on the one onehorse is developing as a Teensy addon board.

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    Assuming it's just for prototyping or situations where power consumption isn't too much of an issue, just pop a low dropout 3.3v linear regulator on your breadboard, fed via Vin (~5v from usb).

    Then feed your peripherals from that rail, rather than the teensy 3.3v.

  7. #7
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    Quote Originally Posted by john2525 View Post
    max current spec for the USB regulator
    In "K20 Sub-Family Reference Manual, Rev. 1.1, Dec 2012" on page 1036

    43.1.2 Features
    • Low drop-out linear voltage regulator with one power channel (3.3V).
    • Low drop-out voltage: 300 mV.
    • Output current: 120 mA.
    • Three different power modes: RUN, STANDBY and SHUTDOWN.
    • Low quiescent current in RUN mode. (Typical value is around 120 uA (one thousand times smaller than the maximum load current).)
    • Very low quiescent current in STANDBY mode. (Typical value is around 1 uA.)
    • Automatic current limiting if the load current is greater than 290 mA.
    • Automatic power-up once some voltage is applied to the regulator input.
    • Pass-through mode for regulator input voltages less than 3.6 V
    • Small output capacitor: 2.2 uF
    • Stable with aluminum, tantalum or ceramic capacitors.


    And in "K20 Sub-Family Data Sheet, Rev. 3, 11/2012." on page 51 (6.8.3 USB VREG electrical specifications) : Maximum load current — Run mode

  8. #8
    Senior Member Jp3141's Avatar
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    Quote Originally Posted by drmpf View Post
    Hi Paul,
    The ESP8266 spec sheet shows > 100mA while transmitting (135mA to 215mA depending on tx power)
    Any suggestions on how to power ESP8266 together with Teensy LC?
    I found the Teensy can't power the ESP8266 reliably -- so I use a MCP1702 (TO-92 3-terminal 3.3 V regulator) to power it from the 5 VUSB.

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