Pro Micro's D2 causing system level problem

Development Boards Arduino
1

There are times when I need to power a 5V/16MHz Pro Micro via the USB but I also have a low resistance between RAW and ground. When the system is operational, power is only applied to RAW so it feeds the Pro Micro’s U2 and this low resistance with around 8V.

The problem is that when powered just from the USB, this low resistance on RAW pulls Vcc down too low via D2. The only fix I see is to physically remove D2. I don’t see any downside to this since SJ1 has continuity and U2 should only be powered by RAW. Please let me know if I’m missing something here.

I think I have located D2 on the board but want a second opinion before I begin surgery. With the USB connector facing away from me, the diode is directly in front of it and centered. It is marked CE and has a band on the right side. My meter confirms that it is a diode with one end connected to RAW and the other to SJ1.

Thanks,

Rick

2

Hi Rick,

You have identified D2 correctly. It is the small black diode directly above (or below in your orientation) the fuse on the Pro Micro. In your set-up, I do not see any issues that removing that diode would cause. It is only there to protect the USB port from voltage provided on RAW so just make sure you leave those pads unconnected so you don’t send your RAW voltage back into your USB port. Otherwise, everything should work just fine with that diode removed on a 5V Pro Micro.