EGS5 Hardware Interface Description
3.8 RTC Backup
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EGS5_HD_v02.004
Page 51 of 123
2012-02-09
Confidential / Released
3.8
RTC Backup
The internal Real Time Clock of EGS5 is supplied from a separate voltage regulator in the an-
alog controller which is also active when EGS5 is in POWER DOWN status. An alarm function
is provided that allows to wake up EGS5 to Airplane mode without logging on to the GSM net-
work.
In addition, you can use the VDDLP line to backup the RTC from an external capacitor or a
battery (rechargeable or non-chargeable). The capacitor is charged by the BATT+ line of
EGS5. If the voltage supply at BATT+ is disconnected the RTC can be powered by the capac-
itor. The size of the capacitor determines the duration of buffering when no voltage is applied
to EGS5, i.e. the larger the capacitor the longer EGS5 will save the date and time.
A serial 1 k
resistor placed on the board next to VDDLP limits the charge current of an empty
capacitor or battery.
The following figures show various sample configurations. Please refer to
for the pa-
rameters required.
Figure 13:
RTC supply from capacitor
Figure 14:
RTC supply from rechargeable battery
Figure 15:
RTC supply from non-chargeable battery
