I have a 6.75V power source. Is this too high to run the Core?
The important line is
Input voltage range [for the regulator] of 3.6 to 6.0v (for 3.3v output)
So it looks like 6.75v is indeed too much for the voltage regulator on the core. You will need to provide your own regulator. In fact, the “absolute max input voltage” Vinmax for the voltage regulator on the Core is 6.5v so 6.75v will absolutely destroy the regulator on the core and thus data the core. Don’t do it
OK, I won’t try it. I’ll get another voltage regulator on there.
Feel free to post back if you have any questions about the regulator you chose. Since the core only consumes 1/2 an amp you could probably get by with a quick trip to radioshack (if you are in the states) to pickup a simple 5V linear regulator.
Diodes work well too they will drop generally 0.6 to 0.7v per diode so 2 in series would drop say 1.2v putting you where you need to be.