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Thread: Connect 5v signals to the GPIO of a Teensy 3.6

  1. #1

    Connect 5v signals to the GPIO of a Teensy 3.6

    Hello

    I need to connect 5v signals to the inputs of Teensy 3.6, that are not 5v tolerant.

    So far I have used an HEF4050 in SOIC, but when trying the CD4050 version in TSSOP I have problems, I think because the propagation time of this chip is quite high, over 140ns.

    I found the 74LVC07, which has a much shorter propagation time, about 2ns, could be a solution. But on the other hand, I have read that the inputs of the Kinetis MK66 have internally an ESD protective diode that I suppose cuts the signal if the current is limited.

    My question is whether it would be enough to put serial resistors to the inputs of the ports to be able to connect 5v signals to the ports of the Teensy 3.6. The alternative is to use a 74LVC07, but if I can do it with resistors much better and cheaper.

    Regards


    " All digital and analog I/O pins are internally clamped to VSS through an ESD protection diode. There is no diode
    connection to VDD. If VIN is less than VSS-0.3V, a current limiting resistor is required. The minimum negative DC
    injection current limiting resistor value is calculated as R=(-0.3-VIN)/|IICDIO| or R=(-0.3-VIN)/|IICAIO|. The actual resistor
    should be an order of magnitude higher to tolerate transient voltages. "

    *
    Last edited by LuisHS; 10-11-2019 at 10:18 AM.

  2. #2
    Senior Member vjmuzik's Avatar
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    If my knowledge is correct then you should be able to do it as long as your resistor value is high enough to limit the current to less than what the Teensy can sink. I’ve done this with external chips before that had the clamp diodes to convert 5v to 3.3v to be used with I2S signals to a Teensy, but I’ve never done it straight to a Teensy. If the Teensy does have the clamp diodes then it should be fine to do it directly just make sure the current isn’t too much.

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