To use the VTG source on QT600, the VTG jumper must be mounted. The on-board VTG source is set from AVR Studio, and can be set to 0V, 1.8V, 2.7V, 3.3V or 5V.
The 5V is limited upwards by the voltage supplied by the USB cable. Depending on the computer or USB HUB used, it can be as low as 4.5V.
Always check the AVR datasheet for operating voltage range before adjusting VTG.
QT600 can supply 100 mA to the target section.
If you are using one of the MCU boards mounted on an STK600 and want the QT600 to supply the power, the STK600's VTG source must be disconnected. Consult the STK600 user guide on how to do this.
If you are using the MCU board stand-alone, QT600 can supply the power.
If you are using a custom MCU board, QT600 can supply the power to the system. Make sure that the current consuption by the whole system does not exceed 100mA.