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 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 ATtiny3217 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
ATtiny3217 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.
Figure 3-6. VBUS Output Voltage vs. Current
3.3.4
Power Supply Exceptions
This is a summary of most exceptions that can occur with the power supply.
Target Voltage Shuts Down
This can happen if the target section draws too much current at a given voltage. This will cause the thermal shutdown
safety feature of the MIC5353 regulator to kick in. To avoid this, reduce the current load of the target section.
Target Voltage Setting is Not Reached
The maximum output voltage is limited by the USB input voltage (specified to be between 4.4V to 5.25V), and the
voltage drop over the MIC5353 regulator at a given voltage setting and current consumption. If a higher output
voltage is needed, use a USB power source that can provide a higher input voltage or use an external voltage supply
on the VTG pin.
ATtiny3217
Curiosity Nano
©
2020 Microchip Technology Inc.
User Guide
DS40002193A-page 16
