The PCF8523 is an ultra-low power RTC with an I²C-bus interface. The device consumes as low as 150nA, typically, at 3 V supply voltage. In addition, the device has battery switch-over, battery low detection and electronic tuning features. The electronic tuning feature was discussed on the previous slide. The battery switch-over circuit monitors the main power supply and automatically switches to the backup supply when a power failure condition is detected. In the standard mode, the switchover occurs when the main supply is less than the backup supply and a threshold voltage. In the direct switching mode, the switchover occurs when the main supply is less than the backup supply voltage. The battery low detection circuit monitors the status of the battery and when the battery voltage goes below a certain threshold value, a flag is set to indicate that the battery must be replaced soon.