4.3.2 External Supply

Instead of the on-board target regulator, an external voltage can power the AVR64EA48 Curiosity Nano. When shorting the Voltage Off (VOFF) pin to the ground (GND) pin, the on-board debugger firmware disables the target regulator, and it is safe to apply an external voltage to the VTG pin.

It is also safe to apply an external voltage to the VTG pin when no USB cable is plugged into the DEBUG connector on the board.

The VOFF pin can be tied low/let go at any time, which will be detected by a pin-change interrupt to the on-board debugger, which controls the target voltage regulator accordingly.

Warning: Applying an external voltage to the VTG pin without shorting VOFF to GND may cause permanent damage to the board.
Warning: Do not apply any voltage to the VOFF pin. Let the pin float to enable the power supply.
Warning: The absolute maximum external voltage is 5.5V for the on-board level shifters, and the standard operating condition of the AVR64EA48 is 1.8–5.5V. Applying a higher voltage may cause permanent damage to the board.
Info: The on-board debugger status LED will blink rapidly and shut the on-board regulator off when applying an external voltage without pulling the VOFF pin low - and an external supply pulls the voltage lower than the monitoring window’s lower limit (target voltage setting – 100 mV). The status LED starts blinking rapidly until the on-board debugger detects the new situation and switches the target voltage regulator back on if suddenly removing an external voltage when the VOFF pin is not pulled low.

Programming, debugging, and data streaming are still possible with an external power supply. The USB cable will power the debugger and signal level shifters. Both regulators, the debugger, and the level shifters are powered down when the USB cable is removed.

Info: In addition to the power consumed by the AVR64EA48 and its peripherals, approximately 100 µA will be drawn from any external power source to power the on-board level shifters and voltage monitor circuitry when a USB cable is plugged into the DEBUG connector on the board. When a USB cable is unplugged, some current is used to supply the level shifter’s voltage pins, which have a worst-case current consumption of approximately 5 µA. Typical values may be as low as 100 nA.