I have been programming my Alchitry Gold board by disconnecting it from my custom PC board (which supplies external power 5V to it). I then plug in a USB cable and program it. Then I disconnect the USB cable, reinstall the Alchitry board to my custom board, and continue testing. Obviously, this is a laborious process that introduces wear to the Alchitry connectors.
I saw a similar forum post where you said it’s not necessary to disconnect the external power source because the Alchitry board has a back current diode D1 (SK34ATR), which prevents external power from being fed back up the USB port.
However, if the external power is turned off and the USB cable is connected, I’m seeing overcurrent problems as the USB port tries to power the Alchitry board, the custom board, my 5V powered analyzer, other interface boards, and the (turned off) power supply. I risk damaging my computer’s USB interface along with the power supply getting back voltage while turned off.
I would like to remove the diode and always require that the setup be externally powered while programming the Alchitry board with a USB cable. I checked the USB chip on the Alchitry board (FT2232HQ), and it appears that it will tolerate back voltage on the USB serial DM,DP pins while it is powered off. I think this configuration will allow me to leave the USB cable connected to the Alchitry board and be free to turn on/off external power as needed.
Having blown up expensive custom boards due to not understanding power supply connections/current flows, I am trying to be super careful here. Is there a flaw in my plan to remove the diode?
Robert