5. Power Supply and Reset
5.1 MCU Power Selection
The EFM32 on the Starter Kit can be powered by one of these sources:
• The debug USB cable; or
• the EFM32's own USB regulator; or
• a 3 V coin cell battery.
The power source for the MCU is selected with the slide switch in the lower left corner of the Starter Kit.
Figure 5.1 Power Switch on
page 13
shows how the different power sources can be selected with the slide switch.
3.3 V
VMCU
AEM
USB
BAT
USB Mini-B
Connector
5 V
3V Lithium Battery
(CR2032)
EFM32
MCU
USB_VREGI
(5V)
USB_VREGO
(3.3V)
.
BA
T
US
B
AEM
LDO
USB Micro-AB
Connector
Advanced
Energy
Monitor
SENSE
Advanced
Energy
Monitor
SENSE
VBUS
Figure 5.1. Power Switch
With the switch in the
AEM
position, a low noise 3.3 V LDO on the Starter Kit is used to power the EFM32. This LDO is again powered
from the debug USB cable. The Advanced Energy Monitor is now connected in series, allowing accurate high speed current measure-
ments and energy debugging/profiling.
With the switch in the
USB
position, the integrated linear regulator in the EFM32 Giant Gecko GG11 MCU is used to power the rest of
the chip as well as the USB PHY with the cable connected to the target USB connector. This allows a USB device application where the
MCU acts as a bus powered device. With the switch in this position, the secondary AEM channel is automatically selected to allow
accurate measurements of the current consumption of the whole application running on USB power.
Finally, with the switch in the
BAT
position, a 20mm coin cell battery in the CR2032 socket can be used to power the device. With the
switch in this position no current measurements are active. This is the recommended switch position when powering the MCU with an
external power source.
Note:
The Advanced Energy Monitor is automatically recalibrated when switching from
AEM
to
USB
or back, which causes the target
EFM32 to lose power for a few seconds.
5.2 Board Controller Power
The board controller is responsible for important features such as the debugger and the Advanced Energy Monitor, and is powered
exclusively through the USB port in the top left corner of the board. This part of the kit resides on a separate power domain, so a differ-
ent power source can be selected for the target device while retaining debugging functionality. This power domain is also isolated to
prevent current leakage from the target power domain when power to the Board Controller is removed.
The board controller power domain is not influenced by the position of the power switch.
The kit has been carefully designed to keep the board controller and the target power domains isolated from each other as one of them
powers down. This ensures that the target EFM32 device will continue to operate in the
USB
and
BAT
modes.
UG287: EFM32 Giant Gecko GG11 Starter Kit User's Guide
Power Supply and Reset
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