Rtc Backup; Figure 12: Rtc Supply From Capacitor; Figure 13: Rtc Supply From Rechargeable Battery; Figure 14: Rtc Supply From Non-Chargeable Battery - Siemens MC45 Manual

MC45 Hardware Interface Description
P R E L I M I N A R Y

3.4 RTC backup

The internal Real Time Clock of MC45 is supplied from a separate voltage regulator in the
power supply ASIC which is also active when MC45 is in POWER DOWN status. An alarm
function is provided for activating and deactivating MC45.
In addition, you can use the VDDLP pin on the board-to-board connector (pin no. 43) to
backup the RTC from an external capacitor or a battery (rechargeable or non-chargeable).
The capacitor is charged by the BATT+ line of MC45. 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 MC45, i.e. the greater
capacitor the longer MC45 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 19 for the parameters required.
MC45_HD_01_V00.02a
Baseband
processor
PSU
RTC

Figure 12: RTC supply from capacitor

Baseband
processor
PSU
RTC

Figure 13: RTC supply from rechargeable battery

Baseband
processor
PSU
RTC

Figure 14: RTC supply from non-chargeable battery

Page 46 of 90
BATT+
B2B
1k
VDDLP
+
BATT+
B2B
1k
VDDLP
+
BATT+
B2B
1k
VDDLP
+
+
12.08.2002