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Tie GPIOs for higher current?

Nate Enos
Genius 9450 points

Hello Tiva Team!

I'm currently trying to drive a series of LEDs with just the Tiva-C 123 Launchpad, and I was curious if it was possible (and safe) to tie together GPIOs to get higher current outputs. Currently I'm outputing 8mA but I would like to get up to 16mA. I see that Tiva-C can sink up to 18mA in certain circumstances however I need to be able to both source and sink 16mA. I have the LEDs connected using a charlieplexing scheme and am only turning on one LED at a time.

So my question is, can I tie togeth GPIOs to get higher current output? I've seen this done with MSP430, but want to check if the same can be done for Tiva-C. Are the GPIOs protected with CLDs? If possible to connect the two pins, are there any risks associated with doing this? (e.g. one goes high first and casues a short, blowing out a pin).

I checked the datasheet and past e2e posts and couldn't find a definite answer. All help is greatly appreciated!

 

Nate

  • 0
    TI__Intellectual 1380 points

    It shouldnt be an issue, would reccomend drawing from different sides of the chip though just to be safe.

    FYI the chip can sink a ton of current, check the max GPIO specs on the datasheet. (you can easily have 18mA of current on one pin if you can live with a VoL of 1.2)

    From the datasheet:

    "For special high-current applications, the GPIO output buffers may be used with the following restrictions. With the GPIO pins configured as 8-mA output drivers, a total of four GPIO outputs may be used to sink current loads up to 18 mA each. At 18-mA sink current loading, the VOL value is specified as 1.2 V. The high-current GPIO package pins must be selected such that there are only a maximum of two per side of the physical package with the total number of high-current GPIO outputs not exceeding four for the entire package"

    -TI Austin

  • 0 in reply to TI Austin
    TI__Genius 9450 points

    Thanks for the help! This was exactly what I needed!

  • 0
    Guru 117855 points

    Unstated in this - and perhaps worthwhile - insure that any GPIO's, "tied together" emanate from the same MCU Port!  Via StellarisWare - or rebrand offshoot - these pins may be masked and thus synchronously set/reset. Pins from different ports cannot achieve this synchronization...thus an active high will "tie" to an active low...never good...

    Having some history w/Led displays - our group does not favor use of any MCU as, "beast of burden." (i.e. direct, higher current, sink/source driver) 

    Favor instead other devices/packages - designed to such purpose.  Often you'll require higher voltages/currents than even "strapped" MCU outputs provide - and this is where purpose designed devices - targeting Leds - most effectively, "shine."