DS1391U-18+

Real Time Clock Overview

The DS1391U-18+ 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 the year 2100. The device operates within an industrial temperature range of -40°C to +85°C and utilizes a 10-pin µSOP package. Key electrical parameters include a supply voltage range of 1.71V to 1.89V, a typical active supply current of 500µA, and a standby current ranging from 60µA to 100µA. The SPI interface supports Modes 1 and 3, operating at frequencies up to 1MHz at this voltage level.

Real Time Clock Feature Summary

• Low-voltage SPI interface supporting Modes 1 and 3 with data rates up to 1MHz at 1.8V
• Integrated reset output and debounced pushbutton input on the RST pin
• Automatic power-fail detection and switching to backup supply (VBACKUP)
• Trickle-charge capability for maintaining backup battery or supercapacitor

Real Time Clock Applications

• Hand-held devices requiring precise timekeeping in low-power environments
• GPS and telematics systems needing embedded time stamping
• Medical devices requiring reliable calendar and alarm functions

Real Time Clock Procurement Notes

Verify component authenticity through authorized distributors as counterfeits exist. Confirm the specific ordering suffix matches the required voltage and package variant. Check for end-of-life status or obsolescence notices from the manufacturer before finalizing procurement plans.

Real Time Clock Selection Notes

Select the DS1391U-18+ when a dedicated reset output and debounced input are required alongside RTC functionality. Ensure the system design accommodates the 1.71V to 1.89V supply range. Verify that the SPI controller supports Mode 1 or Mode 3 protocols for compatible communication.

Real Time Clock Part Context

This component belongs to the DS1390–DS1394 family of low-voltage SPI/3-Wire Real-Time Clocks with Trickle Chargers. The DS1391 variant specifically distinguishes itself by replacing the square-wave/interrupt pin found in other family members with a combined reset output and debounced input function.

Real Time Clock Replacement Considerations

The DS1393U-18+ serves as a functional alternative within the same family, offering similar RTC capabilities but utilizing a 3-wire interface instead of SPI.