Arduino ProMicro Heats up when both usb + 5v VCC feed in

Development Tools IDE 1.x
1

Hello,

I have an Arduino Pro micro

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which works fine when either feed directly from the VCC pin with stable 5V (from a buck converter) or by a laptop through USB.

However if both are connected the board starts heating up very quick.

What is causing this? Is there any way to fix it like putting in some diode on that 5V rail?

Fortunately I only need both connections when I program the arduino from external laptop however then I would have to implement an additional switch which cuts off the 5V input in the meantime :frowning:

2

Also I have noticed a flash corruption issue as well when this happens. It's enough to connect it for just a second on both the code in the arduino gets corrupted and whatever I type in on the serial I will get the response:

CATERIN

I don't know if this is a distorted reply of the commands it should echo back and the main logic is running or the chip is just stuck in a loop where outputs garbage.

However this can be corrected after I re-flash the arduino again.

3

The CATERIN is coming from the bootloader - it's reset itself.

The power supplies are fighting eachother. Probably solvable by putting a diode (schottky of course for the low drop) between external power and Vcc.

4

Yes I figured out this much by now. What I need here is an O Ring:

http://powerblog.vicorpower.com/2013/09/what-is-active-oring/

To be noted, this is such a widely occurring issue that an autoswitching circuit should be added to future Arduinos, I don't even know how they didn't add this yet.