User manual

...the world's most energy friendly microcontrollers
2012-04-24 - Giant Gecko Family - d0053_Rev0.96 113
www.energymicro.com
Figure 10.3. Backup power domain overview
EFM32GG
Main domain
Backup domain
BURTC
BOD
WDOG
POR
EXT
EM4 pin Wake-Up
BURTC
Wake-Up
reset
Wake-up
controller
SW reset
512 byte
ret ent ion
Main power OK
BU_VIN
Main power
Backup power
Main power BOD
RESETn
BU_STAT
BU_VOUT
BUCTRL_EN
PWRCONF_VOUTxxx
BUCTRL_STATEN
VDD_DREG
PWRCONF_PWRRES
BUINACT_PWRCON /
BUACT_PWRCON
+
-
+
-
Main
power
supply
Backup
power
supply
STRONG
MEDIUM
WEAK
BUBODVDDDREG
BUBODBUVIN
Backup regulator
BUBODUNREG
BUBODREG
When in backup mode, available functionality is the same as the functionality available in EM4. Refer
to Section 10.3.4.10 (p. 116) for further details.
10.3.4.2 Brown out detectors
The backup power domain functionality utilizes four brown-out detectors, BODs. One senses the main
power supply, one senses the backup power supply, one senses the unregulated selected power supply
(main or backup, depending on mode), and one BOD senses the regulated power supply. The bits
BUBODVDDDREG ,BUBODBUVIN, BUBODUNREG, and BUBODREG in the RSTCAUSE register in
the RMU are set when the associated BOD triggers. The locations of the Backup BODs are indicated in
Figure 10.3 (p. 113) . A brown out on the main power supply will trigger a switch to the backup power
supply if the backup functionality is enabled and the BOD sensing on the backup power supply has not
triggered. The two other BODs are used for error indication and will only set the bits in RMU_RSTCAUSE
if they are triggered.
10.3.4.3 Entering backup mode
To be able to enter backup mode, the EN bit in EMU_BUCTRL has to be set. The BURDY interrupt
flag will be set as soon as the backup sensing module is operational. Status of the backup functionality
is also available in the BURDY flag in the EMU_STATUS register. The BU_VIN pin also needs to be
enabled. This is done by setting the BUVINPEN bit in EMU_ROUTE. To enter backup mode, the voltage
on VDD_DREG has to drop below the programmable threshold of the BOD sensing on this power. This
threshold is programmed using BUENRANGE and BUENTHRES in EMU_BUINACT. BUENRANGE
decides the voltage range for the BOD, while BUENTHRES is used for tuning of the BOD threshold.
Refer to Section 10.3.4.5 (p. 114) for details regarding BOD calibration.
Note