DS1339U-2+

Real Time Clock Overview

The DS1339U-2+ is a low-power serial real-time clock (RTC) manufactured by Analog Devices Inc./Maxim Integrated. It operates within a supply voltage range of 1.8V to 5.5V and supports an I2C serial interface for data transfer. The device provides timekeeping functions including seconds, minutes, hours, day, date, month, and year with leap-year compensation valid up to the year 2100. It features two programmable time-of-day alarms and a programmable square-wave output. A built-in power-sense circuit automatically switches to a backup supply upon detecting power failures, maintaining time and alarm operations. The component is housed in an 8-pin µSOP package and operates across a temperature range of -40°C to +85°C.

Real Time Clock Feature Summary

• I2C Serial Interface: Supports standard mode (100kHz) and fast mode (400kHz) communication protocols.
• Automatic Power-Fail Detection: Built-in circuitry detects power loss and switches to VBACKUP to maintain timekeeping.
• Dual Alarms: Two programmable time-of-day alarms with configurable mask bits for specific time matches.
• Trickle-Charger Capability: Internal register allows selection of resistor values (250Ω, 2kΩ, 4kΩ) and diode configurations for charging backup sources.

Real Time Clock Applications

• Handheld devices such as GPS units and POS terminals
• Consumer electronics including set-top boxes and digital recorders
• Office equipment like fax machines, printers, and copiers
• Medical devices such as glucometers and medicine dispensers
• Telecommunications infrastructure including routers, switches, and servers

Real Time Clock Procurement Notes

Verify the ordering suffix '+', which indicates a lead-free/RoHS-compliant package. Confirm the voltage variant 'U-2' corresponds to the 1.8V minimum operating requirement. Ensure the 8-pin µSOP package footprint matches the design layout. Check for UL recognition status if safety compliance is required for the specific application environment.

Real Time Clock Selection Notes

Select the DS1339U-2+ when a minimum supply voltage of 1.8V is required, distinguishing it from the U-3 (2.7V min) and U-33 (2.97V min) variants. Ensure the system design accommodates the external 32.768kHz crystal connected to X1 and X2 pins, as this model does not integrate the crystal internally unlike the DS1339C series. Verify that the I2C bus pull-up voltages are compatible with the 5.5V maximum limit on SDA and SCL lines regardless of VCC level.

Real Time Clock Part Context

The DS1339U-2+ belongs to the DS1339 family of serial real-time clocks. It shares functional similarities with the DS1337U+ but adds dual alarms and trickle-charging capabilities. Unlike the DS1339C series, which integrates the crystal in a 16-pin SO package, the U-series utilizes an external crystal in a compact 8-pin µSOP package. This makes the U-2+ suitable for space-constrained designs requiring lower minimum operating voltages than the 3.0V or 3.3V variants.

Real Time Clock Replacement Considerations

Public confirmed substitute part numbers are not available in the provided documentation. The DS1339AU+T and DS1339BU+ are listed in distributor databases but differ in voltage specifications or feature sets; direct substitution requires verification against specific electrical requirements.