General Description
The DS1339B serial real-time clock (RTC) is a lowpower
clock/date device with two programmable timeof-
day alarms and a programmable square-wave output.
Address and data are transferred serially through an I2C
bus. The clock/date provides seconds, minutes, hours,
day, date, month, and year information. The date at the
end of the month is automatically adjusted for months
with fewer than 31 days, including corrections for leap
year. The clock operates in either the 24-hour or 12-hour
format with AM/PM indicator. The device has a built-in
power-sense circuit that detects power failures and automatically
switches to the backup supply, maintaining time,
date, and alarm operation.

Applications
● Handhelds (GPS, POS Terminals)
● Consumer Electronics (Set-Top Box, Digital
Recording, Network Appliance)
● Office Equipment (Fax/Printers, Copier)
● Medical (Glucometer, Medicine Dispenser)
● Telecommunications (Routers, Switches, Servers)
● Other (Utility Meter, Vending Machine,
Thermostat, Modem)

Benefits and Features
●● Drop-In Replacement for DS1339
●● Supports High-ESR Crystals Up to 100kΩ to Allow
Crystals to be Optimized for Cost and Space
●● Completely Manages All Timekeeping Functions
• Real-Time Clock Counts Seconds, Minutes, Hours,
Date of the Month, Month, Day of the Week, and
Year with Leap-Year Compensation Valid Up to
2200
• Two Time-of-Day Alarms
• Programmable Square-Wave Output Signal
●● Low-Power Operation Extends Battery Backup Run Time
• Automatic Power-Fail Detect and Switch Circuitry
●● Simple Serial Port Interfaces to Most Microcontrollers
• I2C Serial Interface
●● Underwriters Laboratories (UL®) Recognized