Question: The EZ-USB® FX3™ ROM bootloader is not recognized on the host PC when the device is in self-powered mode. Why?
The bootloader is designed and coded to operate in bus-powered mode only. The default FX3 ROM bootloader sometimes fails to enumerate and comes up in the Device Manager as “Unknown Device” when operating the device in self-powered mode.
The workaround would be to employ a second-stage bootloader firmware (refer to the “Fx3BootAppGcc” example in the EZ-USB FX3 Software Development Kit) in an I2C/SPI EEPROM and boot from there. Once FX3 boots with this custom bootloader, the application firmware can be downloaded from the PC via the USB interface.