User's Manual

AC65/AC75 Hardware Interface Description
Confidential / Preliminary
s
AC65/AC75_hd_v00.372 Page 52 of 118 2006-08-03
3.8 RTC Backup
The internal Real Time Clock of AC65/AC75 is supplied from a separate voltage regulator in
the analog controller which is also active when AC65/AC75 is in POWER DOWN status. An
alarm function is provided to wake up AC65/AC75 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 AC65/AC75. 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 AC65/AC75, i.e. the larger the capacitor the longer
AC65/AC75 will save the date and time.
A serial 1k 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 26 for the
parameters required.
Baseband
processor
RTC
PSU
+
BATT+
1k
B2B
VDDLP
Figure 13: RTC supply from capacitor
RTC
+
BATT+
1k
B2B
VDDLP
Baseband
processor
PSU
Figure 14: RTC supply from rechargeable battery
RTC
+
+
BATT+
1k
VDDLP
B2B
Baseband
processor
PSU
Figure 15: RTC supply from non-chargeable battery