4. Power Supply and Reset
4.1 MCU Power Selection
The EFM8UB1 Universal Bee MCU on the EFM8UB1-SLSTK2000A is designed to be powered by four different sources:
• Through the on-board debugger.
• Through the EFM8's own USB regulator.
• By a 3 V Battery.
• An externally supplied power source.
Selecting the power source is done with the slide switch in the lower left corner of the board. The figure shows how the different power
sources can be selected with the slide switch.
Figure 4.1. EFM8UB1-SLSTK2000A Power Switch
With the switch in the AEM position, an on-board low noise LDO with a fixed output voltage of 3.3 V is used to power the MCU. This
LDO is powered from the "J-Link" USB cable.
With the switch in the
USB
position, the integrated linear regulator in the EFM8 MCU is used to power the rest of the chip as well as the
USB PHY. This allows a USB device application where the MCU acts as a bus powered device.
With the switch in the BAT position, the device may be powered from either a 20 mm coin cell battery (in the CR2032 socket) or an
external power supply (connected to the VMCU and GND pins on the expansion header).
4.2 MCU Reset
The EFM8 MCU can be reset by a few different sources:
• The RESET button.
• An external debugger by pulling the RSTb pin low.
UG240: EFM8UB1-SLSTK2000A User's Guide
Power Supply and Reset
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