4.5.2 Target Regulator

The target voltage regulator is a MIC5353 variable output LDO. The on-board debugger can adjust the voltage output supplied to the board target section by manipulating the MIC5353’s feedback voltage. The hardware implementation is limited to an approximate voltage range from 1.7V to 5.1V. Additional output voltage limits are configured in the debugger firmware to ensure that the output voltage never exceeds the hardware limits of the PIC18F56Q24 microcontroller. The voltage limits configured in the on-board debugger on PIC18F56Q24 Curiosity Nano are 1.8–5.5V.

Info: The factory default target voltage is 3.3V. The project properties in MPLAB® X IDE can change it. Any change to the target voltage is persistent, even after a power toggle. The resolution is less than 5 mV but may be limited to 10 mV by the adjustment program.
Info: The voltage settings setup in MPLAB® X IDE is not applied immediately to the board. Like clicking the Refresh Debug Tool Status button in the project dashboard tab or programming/reading program memory, the new voltage setting is applied to the board when accessing the debugger.
Info: There is an easy option to adjust the target voltage with a drag-and-drop command text file to the board, which supports a set of commonly used target voltages. See section 3.5.2 Special Commands for further details.

MIC5353 supports a maximum current load of 500 mA. It is an LDO regulator in a small package placed on a small printed circuit board (PCB) and can reach the thermal shutdown condition at lower loads than 500 mA. The maximum current load depends on the input voltage, the selected output voltage, and the ambient temperature. The figure below shows the safe operating area for the regulator, with an input voltage of 5.1V and an ambient temperature of 23°C.

Figure 4-9. Target Regulator Safe Operation Area

The voltage output of the target regulator is continuously monitored (measured) by the on-board debugger. An error condition will be flagged - and the target voltage regulator will be switched off, detecting and handling any short-circuit conditions if it is more than 100 mV over/under the set device voltage. It will also detect and handle if an external voltage, which causes VCC_TARGET to move outside the voltage setting monitoring window of ±100 mV, is suddenly applied to the VTG pin without setting the VOFF pin low.

Info: The on-board debugger has a monitoring window of VCC_TARGET±100 mV, and the status LED will blink rapidly if the external voltage is under this limit. The on-board debugger status LED will continue to shine if the external voltage surpasses this limit. When removing the external voltage, the status LED will start blinking rapidly until the on-board debugger detects the new situation and turns the target voltage regulator back on.