Info:
The on-board debugger has a monitoring window of VCC_TARGET±100 mV. If the external voltage
is measured under this limit, the on-board debugger status LED will blink rapidly. If the external voltage is
measured above this limit, 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
ATmega4809 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
The absolute maximum external voltage is 5.5V for the on-board level shifters, and the standard operating
condition of the ATmega4809 is 1.8–5.5V. Applying a higher voltage may cause permanent damage to the
board.
Info:
If an external voltage is applied 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 on-board
debugger status LED will blink rapidly and shut the on-board regulator off. If an external voltage is
suddenly removed when the VOFF pin is not pulled low, the status LED will start to blink rapidly, until the
on-board debugger detects the new situation and switches the target voltage regulator back on.
Programming, debugging, and data streaming is still possible with an external power supply – the debugger and
signal level shifters will be powered from the USB cable. 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 ATmega4809 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 in the DEBUG connector on the board. When a USB cable is not
plugged in, some current is used to supply the level shifters voltage pins, which have a worst-case current
consumption of approximately 5 µA. Typical values may be as low as 100 nA.
3.3.3
VBUS Output Pin
ATmega4809 Curiosity Nano has a VBUS output pin that can be used to power external components that need a 5V
supply. The VBUS output pin has a PTC fuse to protect the USB against short circuits. A side effect of the PTC fuse
is a voltage drop on the VBUS output with higher current loads. The chart below shows the voltage versus the current
load of the VBUS output.
ATmega4809 Curiosity Nano
Curiosity Nano
©
2020 Microchip Technology Inc.
User Guide
DS50002804B-page 16
