Figure 3-5. Target Regulator Safe Operation Area
The voltage output of the target regulator is continuously monitored (measured) by the on-board debugger. If it is
more than 100 mV over/under the voltage setting value, an error condition will be flagged, and the target voltage
regulator will be turned off. This will detect and handle any short-circuit conditions. It will also detect and handle if an
external voltage which causes VCC_TARGET to move outside of the voltage setting monitoring window of ±100 mV
is suddenly applied to the VTG pin, without setting the VOFF pin low.
Info:
If the external voltage is lower than the monitoring window lower limit (target voltage setting - 100
mV), the on-board debugger status LED will blink rapidly. If the external voltage is higher than the
monitoring window upper limit (target voltage s 100 mV), the on-board debugger status LED will
continue to shine. If the external voltage is removed, the status LED will start to blink rapidly until the on-
board debugger detects the new situation and turns the target voltage regulator back on.
3.3.2
External Supply
AVR128DA48 Curiosity Nano can be powered by an external voltage instead of the on-board target regulator. When
the Voltage Off (VOFF) pin is shorted to ground (GND), 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. This 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
Absolute maximum external voltage is 5.5V for the on-board level shifters, and the standard operating
condition of the AVR128DA48 is 1.8-5.5V. Applying a higher voltage may cause permanent damage to the
board.
AVR128DA48 Curiosity Nano
Curiosity Nano
©
2020 Microchip Technology Inc.
User Guide
DS50002971A-page 15
