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Author Topic: Current limits for the 3v3 and 5V power header pins?  (Read 1535 times)
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What are the documented current sourcing limits for the 3v3 and 5V power header pins on the Due, and where might I find such documentation?
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The 5v regulator is an LM2734 or 36 according to the schematic. That's rated at 1A and a switcher so it may be good at full tilt however the product page says 800mA on both 5v and 3v3 so one has to assume that's correct.

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where might I find such documentation?
The product page

http://arduino.cc/en/Main/ArduinoBoardDue

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Rob
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Rob Gray aka the GRAYnomad www.robgray.com

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The 5v regulator is an LM2734 or 36 according to the schematic. That's rated at 1A and a switcher so it may be good at full tilt however the product page says 800mA on both 5v and 3v3 so one has to assume that's correct.

Thanks Rob. It's good to see a board that finally has decent supply for both voltage rails. I've always considered the feeble 3v3 supply on the 8-bit boards an annoying weakness in the design.

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where might I find such documentation?
The product page

http://arduino.cc/en/Main/ArduinoBoardDue


Thanks for the pointer. Actually, I did try to find this info navigating from the home -- don't know why, couldn't find it.

« Last Edit: November 17, 2012, 06:08:46 pm by pico » Logged

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finally has decent supply for both voltage rails.
The 5v reg is a switcher so that should be good and after all that's where the majority of the heat will happen.

The 3v3 reg is linear in a SOT223 package with a 160 C/W rating, it's rated at 1A but that would depend on how much thermal relief has been provided on the PCB and the ambient temp.

Overall much better than previous Arduinos I think.

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Rob
« Last Edit: November 18, 2012, 12:28:27 pm by Graynomad » Logged

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I personally would make sure to not ask more than half of the 800 ma of either, I prefer to use a separate voltage reg lm78xxx or 79xx for mu devices unless it is a low watt device.
My associate has successfully ran small servos with the 5v but I am not ready to try as smoking the board is pricey. The 3.3v digital pins have a very low limit and the total current of all output pins is accumulative be very careful to respect this. I prefer to use opto isolators and run my devices with isolated power supplies. This keeps the smoke out of my shop for the most part.
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Thanks Rob. It's good to see a board that finally has decent supply for both voltage rails. I've always considered the feeble 3v3 supply on the 8-bit boards an annoying weakness in the design.

The problem is somewhat more complex then would first met the eye, at least for the poor shield developer trying to supply a shield based product to the arduino world that requires use of the 3.3vdc from the attached arduino board has a 'problem' to deal with. The earlier standard arduino boards supplied the 3.3vdc from the on-board FTDI USB serial converter chip and I believe the maximum current capacity was rated as 50ma, with damage to the chip if current draw was exceeded (no overcurrent protection). The present arduino boards use a 3.3vdc voltage regulator so are probably capable of closer to 100-150ma? However any shield made that draws more the 50 ma of 3.3vdc from the shield pin is risking damaging the FTDI chip on older legacy arduino boards. So what is the poor shield developer to do? So it's not unlike the new shield challenge of how to try and support both 5 volt and the new Due 3.3 volt boards with a single shield design. So any commercial shield product use of the arduino shield 3.3V pin is excess of 50 ma carries risk for older arduino boards. Maybe that's why in even the latest arduino Uno product description they still rated the shield 3.3v pin as having a 50 ma maximum rating?

Lefty

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