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)

.

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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