1 General description

The PCF85053A is a CMOS Real-Time Clock (RTC) and calendar optimized for low power consumption and automatic switching to battery on primary power loss. Featuring clock output, ALRT (interrupt) output and 128 bytes of battery backup SRAM. The PCF85053A includes two I2C buses. The primary I2C bus has the read/ write capability on RTC and SRAM registers. The second I2C bus also can read/write most registers with the control bits set by primary I2C controller. The PCF85053A offers clock output calibration-related registers such as crystal CL(capacitive load) configuration and offset register setting.

2 Features and benefits

• Supply voltage: 1.7 V to 3.6 V

• Battery supply voltage: 1.55 V to 3.6 V

• Provides year, month, day, weekday, hours, minutes and seconds based on a 32.768 kHz quartz crystal

• Device addresses

– RTC: 1101 111

– SRAM: 1010 111

• Two independent I2C with speed 400 kHz Max.

– I2C clock Timeout 35 ms max

– Primary I2C bus

– Read/write capability on RTC and SRAM registers

– Active low ALRT (interrupt) output

– Second I2C bus

– Read/write capability on RTC and SRAM registers enabled by primary I2C

• I2C bus not active during battery switchover

• Real-time clock and calendar

• Align to MC146818B Register Definition for Offset 0 to 09h

• Support both Binary Mode and BCD Mode.

• Support 24-hour and 12-hour Mode.

• Support Daylight Saving Mode.

• Interrupt Flag Support

• RTC_CLR Flag

• Alarm Flag

• RTC Fail Flag

• Oscillator Fail Flag

• Battery-backed 128 byte SRAM

• SRAM Clear to ‘0’ by RTC_CLR Pin

• Frequency adjustment via programmable offset register

• Configurable oscillator circuit for a wide variety of quartzes:

CL = 6 pF, CL = 7 pF, and CL = 12.5 pF

• Operating temperature range Tamb: -40 oC to 85 oC

3 Applications

• Server and computer precision timekeeping

• Network-powered and industrial electronics

• Products with long automated unattended operation time

• White goods