The board can be powered from 3 different sources, external power supply, USB VPC and USB USER connector. If two power sources are applied at the same time the following priorities are used to select the current valid power source:
- 1.
External power supply
- 2.
USB VPC
- 3.
USB USER
That means that if an external power supply is connected to the board it has the highest priority and will therefore serve as current power supply. Other power supplies that are connected to the board at the same time will be ignored.
Most parts of the board are powered by a 3.3V on board buck converter. An additional boost converter provides the needed 5V for the TFT display and USB devices that can be connected to the USB USER connector. A power indicator LED, marked with PWR, indicates if the 3.3V from the buck converter are present.
External power supply
An external power supply can be connected to the header J1. The input range is that can be used is between 3.3V and 5V The external power supply input is protected by a diode against wrong polarization of the supply.
USB VPC
The board can be powered by a USB host through the USB connector that is labeled with USB VPC. The host should be able to deliver up to 500 mA in order to supply the board plus additional external devices that can be connected to the board. If more than 500 mA is needed because of power consuming devices like external wireless LAN expansion boards an external power supply should be used on J1.
USB USER
The USB USER connector can also be used to power the board. As described before the board will only be powered from this input if no other power source is connected because it has the lowest priority.
Power indicator LED
The LED marked with PWR signals the connection of a power source. The area marked in the image with power test points can be used to measure the current consumption of the device. The board schematics show which nets are connected by the 0 Ohms resistors to the power supply.