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Wiring for UCM Breakout Board + G400-D


#1

I would like some assistance in the correct wiring for the UCM Breakout Board. I have all the components but want to avoid blowing up the chipset from wrong wiring.

Either there’s little in the way of documentation, or I’ve been unable to find it, so I figured this would be the right place to ask.

The way I understand it, the board requires both 5V and 3.3V. 5V comes from either an external supply, or alternatively, through USB. 3.3V is supplied externally through a step-down.

What I don’t understand is what happens when debugging through the USB. The board appears to be a 3.3V board - how does the debugger communicate if USB is 5V?

Is there a voltage shifter on the G400-D for the USB data lines? If not, the 5V USB data going directly into the module seems like it would harm the chipset, unless I’m missing something. I’d like to be certain of how this works before plugging it in.

Thank you


#2

Here is a link on how to wire up for power on the UCM Breakout Board: https://docs.ghielectronics.com/hardware/ucm/development-options.html (just look under the UCM Breakout Board entry for further details.) As for the USB data, the chipset is designed to deal with the differential signal generated. I hope this helps.


#3

Thanks - I had read that documentation already, but it didn’t say anything about the voltage differences in USB. You’ve allayed my concerns.


#4

Note that you need to provide protection on your board to ensure that the 5V from the USB port is not connected at the same time as any other 5V supply. I like to use ideal diodes for this so that the voltage drop is far less than a normal diode although this is normally only important if you need close to 5V for anything else. :slight_smile: If your design is 3.3V only, no need to worry and a normal 0.5V drop diode will do the job well. Just make sure that the input voltage to the 3.3V regulator has enough headroom. Plenty of Low Drop Out types to choose from.