DS1688S

Real Time Clock Overview

The DS1688S is a serialized real-time clock (RTC) IC designed as a successor to the industry-standard DS1287 PC clock. It operates within a voltage range of +3.0V to +5.0V and provides timekeeping with leap-year compensation valid up to the year 2100. The device integrates 114 bytes of user-accessible non-volatile SRAM, controlled via automatic backup and write protection circuitry using VCCO and CEO pins. Key electrical features include a 64-bit silicon serial number, power-on elapsed timer, power-cycle counter, and auxiliary battery input support.

Real Time Clock Feature Summary

• Serialized Identity: Incorporates a unique 64-bit silicon serial number and supports an additional 64-bit customer-specific ROM or serial number for system identification.
• Power Management Control: Features PWR output pin triggered by date/time alarms or key closures to manage external power supply activation and shutdown.
• External Memory Interface: Provides automatic battery backup and write protection for external SRAM through dedicated VCCO and CEO control pins.
• Maintenance Counters: Includes a 32-bit VCC-powered elapsed time counter, a 32-bit VBAT-powered continuous counter, and a 16-bit power-cycle counter.

Real Time Clock Applications

• PC Real-Time Clocks requiring legacy compatibility with original DS1287 functions.
• Systems requiring electronic identification via unique serial numbers for network node addressing or maintenance tracking.
• Applications utilizing wake-up alarms to trigger system power-on events from standby states.

Real Time Clock Procurement Notes

Verify that the specific order includes the 'S' suffix to confirm the SOIC-28 package variant. Confirm lead-free/RoHS compliance status based on the presence of the '+' designation in the part number. Ensure the design accounts for the multiplexed address/data bus interface requirements when integrating with the host processor.

Real Time Clock Selection Notes

Select the DS1688S over the DS1691 module if the application requires discrete integration of an external crystal and lithium battery rather than a self-contained unit. This component is suitable for designs needing precise control over external SRAM power sequencing. Verify that the host system can support the required multiplexed bus timing and address strobe signals defined in the datasheet.

Real Time Clock Part Context

The DS1688S belongs to the DS1688/DS1691 family of serialized RTCs manufactured by Analog Devices Inc./Maxim Integrated. It serves as a direct functional replacement for older DS1285, DS1385, DS1485, and DS1585 clocks while adding modern serialization and enhanced power management capabilities. The 'S' suffix specifically denotes the 28-pin Small Outline (SO) package configuration.

Real Time Clock Replacement Considerations

Public confirmed substitute part numbers are not available in the provided documentation.