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Thread: Maximum current for 2++ Board?

  1. #1

    Maximum current for 2++ Board?

    Hi guys,

    I have a Teensy 2++ and use 14 LEDs (20 mA) and 5 encoders (they have 5k resistors).
    The datasheet says that each pin can deliver 40mA, the GND-pin 200mA. That means
    that I am limited by the GND-pin, right? So I can light up a maximum of 5 LEDs or the Teensy
    will break?

    How much current do the encoders draw, 5V/5000 Ohm = 1 mA, right?

    Thanks,

    Olli

  2. #2
    Senior Member PaulStoffregen's Avatar
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    The recommended maximum is 20 mA per pin.

    The datasheet says 40 mA "absolute maximum". This 40 mA number, and even 50 mA, is widely published in the Arduino world. But running above 20 mA for extended periods of time is not advisable.

  3. #3
    So... 200mA on GND-pin means I can light up up to 10 (not 5, as I wrote above) LEDs at the same time, right?
    Connecting 15 LEDs and lighting them up at the same time will burn the Atmel?

  4. #4
    Senior Member Ben's Avatar
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    You propably wouldn't instantly fry the chip, but it's likely the chip will get damaged over time either due to thermal hot spots or due to a to high current density in the chips metal layers and/or silicon. If you want to have more than 10 LEDs on at the same time, you basically have two options: Increase the value of the current limiting resistor, so each LED draws less current, or light one LED after the other with the full current in a fast cycle, so it seems to the eye as if they were on at the same time (persistence of vision, POV).
    Ben
    Last edited by Ben; 08-01-2013 at 10:00 AM. Reason: typos

  5. #5
    Ah, very good. I have 14 LEDs connected to it, basically I should just abstain from testing them at the same time.
    In normal operation, only 2-5 LEDs will be on. Thanks, guys!

  6. #6
    Senior Member PaulStoffregen's Avatar
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    Another trick you can use for more LEDs and still stay within the conservative guidelines involves connecting half from the pin to ground and the other half from their pins to VCC. Half the LEDs have current flow through the chip's VCC pin and flowing out the I/O pin. The other half have current flow into their I/O pin and through the chip to GND.

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