User's Manual

MC46 Hardware Interface Description
DRAFT
MC46_HD_V02.8xb Page 47 of 98 21.08.2003
3.8 RTC backup
The internal Real Time Clock of MC46 is supplied from a separate voltage regulator in the
power supply ASIC which is also active when MC46 is in POWER DOWN status. An alarm
function is provided that allows to wake up MC46 without logging on to the GSM network.
In addition, you can use the VDDLP pin on the board-to-board connector to backup the RTC
from an external capacitor or a battery (rechargeable or non-chargeable). The capacitor is
charged by the BATT+ line of MC46. If the voltage supply at BATT+ is disconnected the
RTC can be powered by the capacitor. The size of the capacitor determines the duration of
buffering when no voltage is applied to MC46, i.e. the greater capacitor the longer MC46 will
save the date and time.
The following figures show various sample configurations. The voltage applied at VDDLP
can be in the range from 2 to 5.5V. Please refer to Table 27 for the parameters required.
Baseband
processor
RTC
PSU
+
BATT+
1k
B2B
VDDLP
Figure 12: RTC supply from capacitor
RTC
PSU
+
BATT+
1k
B2B
VDDLP
Baseband
processor
Figure 13: RTC supply from rechargeable battery
RTC
PSU
+
+
BATT+
1k
VDDLP
B2B
Baseband
processor
Figure 14: RTC supply from non-chargeable battery