> 3.8 | 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 1 kΩ 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 30 for the parameters required.
> Figure 14: RTC supply from capacitor
> Figure 15: RTC supply from rechargeable battery
> Figure 16: RTC supply from non-chargeable battery