General description
The PCF8523 is a CMOS1 Real-Time Clock (RTC) and calendar optimized for low power consumption. Data is transferred serially via an I2C-bus with a maximum data rate of 1000 kbit/s. Alarm and timer functions are available with the possibility to generate a wake-up signal on an interrupt pin. An offset register allows fine-tuning of the clock. The PCF8523 has a backup battery switch-over circuit, which detects power failures and automatically switches to the battery supply when a power failure occurs.

Features and benefits
■ Provides year, month, day, weekday, hours, minutes, and seconds based on a 32.768 kHz quartz crystal
■ Resolution: seconds to years
■ Clock operating voltage: 1.0 V to 5.5 V
■ Low backup current: typical 150 nA at VDD = 3.0 V and Tamb = 25°C
■ 2 line bidirectional 1 MHz Fast-mode Plus (Fm+) I2C interface, read D1h, write D0h2
■ Battery backup input pin and switch-over circuit
■ Freely programmable timer and alarm with interrupt capability
■ Selectable integrated oscillator load capacitors for CL = 7 pF or CL = 12.5 pF
■ Internal Power-On Reset (POR)
■ Open-drain interrupt or clock output pins
■ Programmable offset register for frequency adjustment

Applications
■ Time keeping application
■ Battery powered devices
■ Metering