Built in frequency adjusted 32.768 kHz crystal unit
The VDD voltage is monitored and it switches to the backup power supply by the automatic operation. The switch voltage to the backup power supply. 1.25V (Min.). Even if the main power supply voltage is decreased, the current flow from the backup power supply is prevented. When the main power is supplied, reset output is released.The release voltage is selected by the register. (2.80V / 2.75V). Delay time from the voltage rise detection is 60ms Typ.
Key Features

Built in frequency adjusted 32.768 kHz crystal unit

Interface Type: I2C-Bus interface

Interface voltage range: 1.6V to 5.5V

Wide voltage for time keeping: 1.1V to 5.5V

Low backup current: 300 nA ( Typ. ) / 3 V

Auto power switching function:Switchover by main power supply monitor.

Backup battery charge control function: For the rechargeable lithium batteries.

Reset functions with a delay:Detect a main power supply and remove the reset.

The various function include full calendar, alarm, timer, etc.

Epson prepared Linux driver for development
https://www5.epsondevice.com/en/information/support/linux_rtc/
The registered trademark Linux is used pursuant to a sublicense from LMI(Linux Mark Institute)

* The I2C-BUS is a trademark of NXP Semiconductors.

Resources
Datasheet