Rtc Backup; Figure 9: Rtc Supply From Capacitor; Figure 10: Rtc Supply From Rechargeable Battery; Figure 11: Rtc Supply From Non-Chargeable Battery - Siemens TC65 Hardware Interface Description

TC65 Hardware Interface Description
Strictly confidential / Draft
3.7

RTC Backup

The internal Real Time Clock of TC65 is supplied from a separate voltage regulator in the
analog controller which is also active when TC65 is in POWER DOWN status. An alarm
function is provided that allows to wake up TC65 to Airplane mode 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 TC65. 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 TC65, i.e. the larger the capacitor the longer TC65
will save the date and time.
A serial 1kΩ 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 Table 17 for the
parameters required.
TC65_HD_V00.521
Baseband
processor
PSU
RTC

Figure 9: RTC supply from capacitor

Baseband
processor
PSU
RTC

Figure 10: RTC supply from rechargeable battery

Baseband
processor
PSU
RTC

Figure 11: RTC supply from non-chargeable battery

Page 43 of 99
BATT+
B2B
1k
VDDLP
+
BATT+
B2B
1k
VDDLP
+
BATT+
B2B
1k
VDDLP
+
+
s
24.05.2005