DS1391U-3+

Real Time Clock Overview

The DS1391U-3+ is a low-voltage serial peripheral interface (SPI) real-time clock/calendar manufactured by Analog Devices Inc./Maxim Integrated. It provides hundredths of a second, seconds, minutes, hours, day, date, month, and year information with automatic leap-year compensation valid up to 2100. The device operates on an SPI-compatible bidirectional bus supporting Modes 1 and 3 at frequencies up to 4MHz at 3.0V/3.3V. It features a programmable time-of-day alarm, trickle-charging capability for backup sources, and power-fail detection with automatic switching to VBACKUP. The unit includes a reset output/debounced input pin and is housed in a 10-pin µSOP package.

Real Time Clock Feature Summary

• SPI Interface: Supports Modes 1 and 3 with SCLK frequencies up to 4MHz at 3.0V/3.3V and 1MHz at 1.8V.
• Timekeeping: Counts hundredths of seconds through year with BCD format and automatic leap-year correction.
• Power Management: Includes power-fail detect circuitry that switches to VBACKUP supply; supports trickle charging via selectable resistors.
• Reset Functionality: Features an RST pin acting as both an active-low open-drain output for power status and a debounced pushbutton input.

Real Time Clock Applications

• Hand-Held Devices
• GPS/Telematics Devices
• Embedded Time Stamping
• Medical Devices

Real Time Clock Procurement Notes

Verify the specific ordering suffix '-3+' corresponds to the 2.7V to 3.3V voltage range variant when sourcing. Confirm package availability in the 10-pin µSOP configuration. Check current production status as legacy Maxim Integrated products may have transitioned or reached end-of-life stages depending on the manufacturing batch date code.

Real Time Clock Selection Notes

Select the DS1391U-3+ over other family members when an SPI interface is required alongside a dedicated reset output rather than a square wave/interrupt pin. Ensure the system voltage aligns with the 2.7V to 3.3V operating range. Consider the DS1390 if an SQW/INT pin is preferred over the RST function, or the DS1394 if SPI Modes 0 and 2 are necessary.

Real Time Clock Part Context

This component belongs to the DS1390–DS1394 series of low-voltage RTCs. The DS1391 specifically differentiates itself within this group by replacing the SQW/INT pin found on the DS1390 with an RST output/debounced input. It shares the same SPI interface architecture and core timekeeping capabilities as its siblings but offers distinct pinout functionality for system reset management.

Real Time Clock Replacement Considerations

Public confirmed substitute part numbers are not available in the provided documentation. The datasheet references the DS1390, DS1392, DS1393, and DS1394 as functional variants within the same family, but does not list external cross-references or direct replacements for the DS1391U-3+.