3v3 input to BX?


Looking at the schematic, it seems that I can power the BX with a 3v3 power supply using the 3v3 pin (since the power rails to the rest of my circuit are 3v3 also). If I leave the Vin pin disconnected, that shouldn’t blow up the 3v3 regulator, right?


Should work just fine. Just be careful if you power the 3.3v rail externally and also want to connect a USB cable.


What precautions should you take in that instance? What’s the best way to externally power the device and still be able to have USB comms to it?


That’s a good question. In my application I’d like to have the USB connected for data, but power the circuit using an external 3v3 supply. I definitely don’t want the circuit powered by USB.

I think I’m just going to leave the Tiny’s 3v3 pins unconnected. It means that I must have USB connected for the board to work, but that’s not a problem for me.


The question was more for Luke - what’s an appropriate way to power the FPGA externally while connected to a USB port? Some systems use a diode to prevent contention when USB and a Vin are both used, but I don’t see that on the BX schematic.


I’ve been thinking about this. I think the simplest solution can be found here:


I would recommend option #2: modify a USB cable by cutting the red wire. This will modify a relatively cheap USB cable vs the more expensive TinyFPGA BX.

Option #1 on the BX would be removing the 3.3v regulator. I wouldn’t recommend it unless you have a hot air tool.