Hello JH W,
The FX3 SDK available on the web does not have the CPP code/ the executable to download firmware hex into the RAM. The next version of the FX3 SDK (Version 1.3.4), contains the fwDownload_fx2, fwDownload_fx3 applications. These applications are based on C++ and can be used to download the firmware hex file into the FX2LP/FX3 RAM.
Please visit EZ-USB FX3 Software Development Kit for updates on the FX3 SDK.