User manual

...the world's most energy friendly microcontrollers
2012-04-24 - Giant Gecko Family - d0053_Rev0.96 115
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Figure 10.5. BOD calibration using DAC
1.8V
+
-
BUCTRL_BODCAL
DAC alternative output
VDD_DREG
BOD trigger
0
1
EMU_BUINACT_BUENRANGE /
EMU_BUINACT_BUENTHRES
10.3.4.6 Backup battery charging
The EFM32GG includes functionality for charging of the backup battery. This is done by connecting
the main power and the backup power through a resistor, and optionally a diode. The connection is
configured individually for when in backup mode and when in normal mode. When in normal mode, the
connection is configured in PWRCON in EMU_BUINACT. PWRCON in EMU_BUACT configures the
connection when in backup mode. The series resistance between the two power domains is configured
in PWRRES in EMU_PWRCONF, this configuration applies both to backup mode and normal mode.
10.3.4.7 Supply voltage output
To be able to power external devices, the supply voltage for the backup domain is available as an output.
Three switches connect the backup supply voltage to the BU_VOUT pin. To be able to control the series
resistance, the switches have different strengths: weak, medium, and strong. The switches are controlled
using the VOUTWEAK, VOUTMED, and VOUTSTRONG bits in EMU_PWRCONF. For resistor values,
refer to Device Datasheet Electrical Characteristics.
10.3.4.8 Voltage probing
It is possible to probe the voltage levels at VDD_DREG, BU_VIN, and BU_VOUT. This is done by
configuring the ADC to measure a tristated channel, for instance a disabled DAC channel. The PROBE
bitfield in EMU_BUCTRL configures which voltage to be probed. The voltage measured by the ADC will
be 1/8 of the actual probed voltage, meaning that the result needs to be multiplied by 8 for the correct
result. Voltage probing does not work when BODCAL in the EMU_BUCTRL register is set.
10.3.4.9 Configuration lock
Configurations used in Backup mode and EM4, like BOD calibration, and Backup RTC settings need
to be locked before entering EM4, this is done by setting the LOCKCONF bit in EMU_EM4CONF. This
bit should also be set before a potential entry to backup mode. Setting this bit will lock following the
configuration:
• LFXOMODE, LFXOBUFCUR, and LFXOBOOST in CMU_CTRL
• REDLFXOBOOST in EMU_AUXCTRL
• TUNING in CMU_LFRCOCTRL
• BURSTEN in RMU_CTRL
• BURTCWU and VREGEN in EMU_EM4CONF
• EMU_BUCTRL
• EMU_PWRCONF
• EMU_BUINACT
• EMU_BUACT
• EMU_ROUTE
Note
For registers residing in the CMU and EMU_AUXCTRL, the reset value will be read after
exit from EM4 or Backup mode, but if LOCKCONF in EMU_EM4CONF has been set, the