3.3.1
Target Voltage Regulator
The target voltage regulator is a MIC5353 variable output LDO. The On-Board Nano Debugger can adjust the voltage
output that is supplied to the kit target section by manipulating the MIC5353's feedback voltage. The hardware
implementation is limited to an approximate voltage range from 1.7V-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
SAMD21G17D microcontroller. The voltage limits configured in the On-Board Nano Debugger on the SAM D21
Curiosity Nano are 1.7V-3.6 V. The target voltage is set to 3.3V in production and can be changed through Atmel
Studio. Any change to the target voltage done in Atmel Studio is persistent, even through a power toggle. The
MIC5353 supports a maximum current load of 500 mA. It is an LDO regulator in a small package, placed on a small
PCB, and the thermal shutdown condition can be reached at lower loads than 500 mA. The maximum current load
depends on the input voltage, set output voltage, and the ambient temperature. The following figure shows the safe
operation area for the regulator with an input voltage of 5.1V and an ambient temperature of 23°C.
Figure 3-3. Target Regulator Safe Operation Area
3.3.2
External Supply
The SAM D21 Curiosity Nano evaluation kit 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 Nano Debugger firmware
disables the target regulator and it is safe to apply an external voltage to the VTG pin.
WARNING
Applying an external voltage to the VTG pin without shorting VOFF to GND may cause permanent damage
to the kit.
WARNING
Absolute maximum external voltage is 5.5V for the level shifters on board. Applying a higher voltage may
cause permanent damage to the kit.
Programming, debugging, and data streaming are still possible while using the external power. 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.
SAM D21
Curiosity Nano
©
2020 Microchip Technology Inc.
User Guide
DS70005409C-page 8
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