Specifications

AC65/AC75 Hardware Interface Description
3.8 RTC Backup
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AC65_AC75_HD_v01.002 Page 49 of 117 2006-10-30
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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 that allows 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
Ω resistor placed on the board next to VDDLP limits the charge current of an empty capacitor or bat-
tery.
The following figures show various sample configurations. Please refer to Table 26 for the parameters required.
Figure 13: RTC supply from capacitor
Figure 14: RTC supply from rechargeable battery
Figure 15: RTC supply from non-chargeable battery