3.2 Power Supply
The Thunderboard EFM32GG12 can be either bus-powered or self-powered depending on the position of the slide switch marked
"PWR" located in the lower right corner of the board. Both these modes are explained in detail below.
3.2.1 Self-Powered Mode
When the "PWR" slide switch is in the "DBG USB" position, the Thunderboard EFM32GG12 is set up in self-powered mode with its
internal regulator disabled. In this configuration, the EFM32GG12 and the VMCU net are powered by an on-board regulator which
draws power from the USB Micro-B debugging connector. The low-dropout regulator has a total output current capacity of 300 mA,
where some of it is being used to power the on-board debugger through the 3V3 net.
VMCU
DBG USB
LDO
3V3
Power Source
DBG
USB
EFM32GG12
5V
VBUS
EFM USB
LDO
IOVDD
AVDD
VREGVDD
VREGSW
DVDD
VBUS
VREGI
VREGO
VDCDC
Figure 3.2. Self-powered Mode
3.2.2 Bus-Powered Mode
When the "PWR" slide switch is in the "MCU USB" position, the EFM32GG12 is set up in bus-powered mode. In this configuration, the
EFM32GG12 and the VMCU net are powered by the EFM32's internal 5V-to-3.3 V regulator. The input of the internal regulator (VREGI)
is connected to the VBUS line of the USB Micro-B connector that connects to the EFM32GG12's USB peripheral.
VMCU
DBG USB
LDO
3V3
Power Source
EFM32GG12
5V
VBUS
EFM USB
LDO
IOVDD
AVDD
VREGVDD
VREGSW
DVDD
VBUS
VREGI
VREGO
VDCDC
Isolated from VMCU
MCU
USB
Figure 3.3. Bus-powered Mode
UG371: Thunderboard EFM32GG12 User's Guide
Hardware
silabs.com
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