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Can the AM1808 directly drive LEDs?

Gloria Mattson
Prodigy 80 points
Other Parts Discussed in Thread: AM1808

Can the AM1808 source the current required to directly drive a few LEDs with GPIO?  Does the I(OH)/(OL) spec of +/- 6 mA max mean that it is not really practical since most common LEDs require at least 4 or 5 mA to light, and I need to keep my current limiting resistor and Vf tolerances such that I never exceed 6 mA, or am I reading that spec wrong (section 5.3 on pg 68)?

  • 0
    Prodigy 80 points

    Basically I am asking if 6 mA truly is the most that a GPIO pin could source/sink?

    One other way to do this might be to use two GPIO pins for one LED.  Would this work, or are there synchronicity issues? 

    Anyone have any other tips on how to do this without adding extra external circuitry?  I have plenty of extra pins on the processor, but not much room left on the PCB.  The LEDs will be used simply for debug/status so if they are dim, it could be fine.

  • 0 in reply to Gloria Mattson
    Genius 3685 points

    6mA is the max , which shouldn't be crossed. The idea of using two IO's might work, but to be honest I have never tried it and wouldn't recommend it, and you of cause would need to switch the two IOs simultaniously => The IOs need to be controller by the same register in the GPIO block of AM18108.

    All this being said. I would strongly recommend adding a small FET or BJT in series with the LED and thereby avoid all problems instead. In case you can't find space (somewhere on the PCB) for something like a single http://www.semicon.panasonic.co.jp/ds4/SJJ00002BED_discon.pdf or http://www.toshiba.com/taec/components2/Datasheet_Sync//52/6111.pdf for every two LEDs I think you should consider if your PCB isn't already too highly packed :-)

    Best regards - Good luck
      Søren