An external voltage instead of the on-board target regulator can power the PIC18F57Q43 Curiosity Nano. 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 PIC18F57Q43 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 PIC18F57Q43 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.
