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Sinking 5V external LEDs through the 3.3 V MCU on the Freedom board?

Question asked by injunear on Nov 12, 2012
Latest reply on Dec 5, 2012 by Peter Dvorak

I have four external LEDs connected to pin 10 of J9 (USB +5V). It is my intention to turn them on by providing ground through pins 9, 11, 13, & 15 of J9 (PTE2, PTE3, PTE4 & PTE5 respectively). I am able to turn them on as desired and the logic to turn them off is also working. However, when off they are still dimly lit. Could this be because when high (LED OFF mode) the CPU pins are at 3.3 volts and they are still sinking the LEDs attached to 5V from the USB?

 

Could this be damaging the CPU?

 

From what I have read so far, the CPU is engineered very well so I hope this kind of potential electrical error has not baked the silicon.

 

Nevertheless, is this why my LEDs are still slightly on when I want them to be off?

 

What would be a good way to work around this issue? Should I source all 4 of them at pin 4 or 8 P3V3? What is the current capability of P3V3?

 

Thank you.

 

BTW,   Freescale - I think you have hit a home run with this eval board. That includes the price. I can imagine countless adolescents and wannabees (as well as innumerable professionals) hacking this board to pieces because of its versatility and cost.

 

(Perhaps you can offer a kit for under $30 that includes headers on the board and an IO box with a few LEDs and switches, and a getting started manual to explain the details of making it all work together.)

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