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Topic: how much current can 5V and 3.3V outputs deliver when USB powered (Read 270 times) previous topic - next topic


I'm hoping to use a Due to control 2 Linear Technology DC1705 frequency synthesizer demo boards over the SPI interface. The DC1705 boards require 5V @ 50mA  & 3.3V @ 115 mA each for power (Linear was too cheap to put a 50 cent 5->3.3V regulator on this $125 board.) I thought I'd use the 5V & 3.3V outputs of the Due.  The Due spec says the 3.3V regulator can deliver 800mA but some of that goes to the CPU. How much is left for this output (assuming the current draw on the other lines is negligible) ? And there is no mention of how much current the 5V output can deliver. What is it?


The 5V output can deliver whatever's left over from the USB supply after the
3.3V switching regulator has taken its share...  So 0.5A - x

Rough calculations show your boards take 0.63W each - the USB can give
2.5W max (0.5A), my Due takes about 0.13A, so 0.65W.

Therefore 2.5 - 0.65 = 1.85W available, assuming switching regulator is 80%
efficient that's about 1.5W spare for the 2 boards.

I think its OK - but there's only one true test!
[ I won't respond to messages, use the forum please ]

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