DS1689S

Real Time Clock Overview

The DS1689S is a serialized real-time clock (RTC) IC designed for +3V or +5V operation. It features a multiplexed address/data bus interface and includes 114 bytes of user non-volatile RAM. The device incorporates a unique 64-bit silicon serial number and an additional 64-bit customer-specific ROM. Key enhancements over the DS1287 include automatic battery backup, write protection for external SRAM via VCCO/CEO pins, power control circuitry for system wake-up, and a century register. It supports leap year compensation valid through 2100 and operates within a commercial temperature range of 0°C to +70°C in a 28-pin SOIC package.

Real Time Clock Feature Summary

• Integrated 114-byte Non-Volatile RAM with automatic backup and write protection for external SRAM
• Unique 64-bit Silicon Serial Number plus 64-bit Customer Specific ROM
• Power Control Circuitry supporting system power-on via date/time alarm or key closure
• +3V or +5V Operation with autosense voltage detection

Real Time Clock Applications

• PC Clocks and Motherboards
• Industrial Data Logging Systems
• Network Node Identification
• Warranty Tracking Modules

Real Time Clock Procurement Notes

Verify component authenticity as the DS1689S is a legacy part from Analog Devices/Maxim Integrated. Confirm that the specific orderable suffix matches the required temperature grade (SN for industrial -40°C to +85°C vs S for commercial 0°C to +70°C). Ensure the presence of the '+' symbol indicates RoHS compliance if environmental regulations apply to the assembly process.

Real Time Clock Selection Notes

Select the DS1689S when a direct replacement for the DS1287 is needed with added serialization and NV RAM capabilities. Choose the SN variant for applications requiring operation below 0°C. Ensure the design accommodates the multiplexed bus timing requirements and provides appropriate crystal load capacitance (6pF or 12.5pF) on the X1/X2 pins.

Real Time Clock Part Context

The DS1689S belongs to the Dallas Semiconductor RTC family, succeeding the industry-standard DS1287. It is functionally compatible with existing BIOS implementations for original DS1287 functions while adding modern features like elapsed time counters and power cycle counting. The standalone IC version (DS1689) differs from the module version (DS1693), which integrates the crystal and battery.

Real Time Clock Replacement Considerations

The DS1689S is a pin-compatible successor to the DS1287. Verify that the target system supports the multiplexed bus architecture and that the voltage selection logic (PSEL pin) aligns with the main supply rails.