I'm currently working on a project using a UDOO and control panel containing lots of LEDs/LCDs . . . The front Panel needs about 2.5amp worst case at 3.3 volts + 200mA at 5v. I'm presuming but can't find any info to confirm this that UDOO can't provide 2.5amp at 3.3 volts . . . Please could someone clarify. If more power is required to run 3v3 peripherals then I will add external 3v3 PSU but not sure whether UDOO will mind me paralleling this with internal power supply . . .
The 3.3V rail is provided by a RT8287A switching buck regulator, which is rated for 4A max. From this you'd need to subtract the demand from 3.3V logic on the board itself-- I'd reserve 1A for that, though actual demand should be less. So, you might be able to squeeze out 2.5A for your panel, though this voltage is only available on two Arduino pins (+3.3V and IOREF) so there could be significant voltage drop at that level. Paralleling two power supplies, especially switchmode ones is never a good idea, unless they're designed for that with current-sharing diodes, remote sense feedback, etc. If you do end up with an outboard +3.3V source, it should be kept isolated from the Udoo's 3.3V rail, but with the grounds bonded together.
