Instead of the on-board target regulator, an external voltage can power the PIC16F17146 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 PIC16F17146 is 1.8–5.5V. Applying a higher voltage may cause permanent damage to the board.
Info: The on-board
debugger monitors the voltage supplied to the board. If VOFF is
not pulled low and external power is supplied that differs by
more than ±100 mV from the target regulator setting, the
on-board debugger will shut off the target regulator and begin
blinking the status LED rapidly, indicating an error condition.
Once the input voltage returns to within ±100 mV of the target
regulator setting, the on-board debugger will switch on the
target regulator and stop blinking the status LED.
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 PIC16F17146 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 plugging a USB cable 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, having a worst-case current consumption of
approximately 5 µA. Typical values may be as low as 100 nA.
