How to Power On Texas Instruments Tiva launchpad?
there is a detail from this documentation, provided by Texas Instruments.



In the final pages of this document are the circuit diagrams of the device.
As you can see in detail, + VBUS connection is taken from the ICDI section or from the USB connection associated to the microcontroller.
This means that you can select with the switch, the source of power supply, from emulation block or from the external USB.
Then, the voltage level +VBUS enters a + 3.3V regulator that feeds the microcontroller. In short, you can connect an external source of 5V on the +VBUS pin, but you must be careful not to connect power from the emulator block, to avoid conflicts.

You may need to adapt your application allowing you to select the external power supply (through the VBUS pin) or from block emulation, to monitor the implementation of the software in the hardware implementation.

Note
It is very important that the two GND pins are connected when using external power.