26
XMEGA A3BU [DATASHEET]
8362F–AVR–02/2013
14.
Battery Backup System
14.1
Features
Battery Backup voltage supply from dedicated VBAT power pin for:
One Ultra Low-power 32-bit Real Time Counter (RTC)
One 32.768kHz crystal oscillator with failure detection monitor
Two Backup Registers
Typical power consumption of 500nA with Real Time Counter running
Automatic switching from main power to battery backup power at:
Brown-Out Detection (BOD) reset
Automatic switching from battery backup power to main power:
Device reset after Brown-Out Reset (BOR) is released
Device reset after Power-On Reset (POR) and BOR is released
14.2
Overview
Atmel AVR XMEGA family is already running in an ultra low leakage process with power-save current consumption below
2A with RTC, BOD and watchdog enabled. Still, for some applications where time keeping is important, the system
would have one main battery or power source used for day to day tasks, and one backup battery power for the time
keeping functionality. The Battery Backup System includes functionality that enable automatic power switching between
The Battery Backup Module support connection of a backup battery to the dedicated VBAT power pin. This will ensure
power to the 32-bit Real Time Counter, a 32.768kHz crystal oscillator with failure detection monitor and two backup
registers, when the main battery or power source is unavailable.
Upon main power loss the device will automatically detect this and the Battery Backup Module will switch to be powered
from the VBAT pin. After main power has been restored and both main POR and BOR are released, the Battery Backup
Module will automatically switch back to be powered from main power again.
The 32-bit real time counter (RTC) must be clocked from the 1Hz output of a 32.768kHz crystal oscillator connected
between the TOSC1 and TOSC2 pins when running from VBAT. For more details on the 32-bit RTC refer to the “RTC32 –