DS17485-3

Real Time Clock Overview

The DS17485-3 is a real-time clock (RTC) designed as a successor to the industry-standard DS12885 and DS12887. It provides a multiplexed byte-wide interface for accessing time, calendar, alarm, and control registers. The device includes 114 bytes of general-purpose battery-backed NV SRAM and 4096 bytes of extended battery-backed NV SRAM. It features a silicon serial number, power-on/off control circuitry, and a programmable square-wave output. The RTC counts seconds through years with leap-year compensation valid through 2099. It supports optional +3.0V or +5.0V operation, with automatic switching to backup supplies upon primary power failure.

Real Time Clock Feature Summary

• Incorporates industry-standard DS12887 PC clock functions plus enhanced features like a 64-bit silicon serial number and SMI recovery stack.
• Provides 114 bytes of general-purpose NV SRAM and 4096 bytes of extended battery-backed NV SRAM.
• Features power-control circuitry that supports system power-on from a date/time alarm or key closure via the PWR output pin.
• Includes automatic power-fail detect and switch circuitry, maintaining timekeeping via VBAT or VBAUX inputs when VCC drops below the trip point.

Real Time Clock Applications

• Embedded Systems
• Utility Meters
• Security Systems
• Network Hubs, Bridges, and Routers

Real Time Clock Procurement Notes

Verify component authenticity and datasheet revision status prior to integration. Confirm voltage selection suffixes (-3 for 3V, -5 for 5V) match system requirements. Check for end-of-life status or obsolescence notices from Analog Devices/Maxim Integrated. Ensure proper handling of lithium battery connections to avoid reverse charging issues.

Real Time Clock Selection Notes

Select the DS17485-3 for applications requiring 4KB of extended nonvolatile RAM and precise timekeeping with leap-year correction. Choose this part over the DS17285 if larger memory capacity is needed, or over the DS17487 if an external crystal and battery are preferred over an encapsulated module. Verify compatibility with existing BIOS software for original DS1287 functions if migrating legacy designs.

Real Time Clock Part Context

The DS17485 belongs to the DS17x85 family of real-time clocks, which also includes the DS17285 and DS17885. These devices are successors to the DS12885 and DS12887 standards. The DS17485 specifically differentiates itself by offering 4KB of extended NV SRAM, whereas the DS17285 offers 2KB and the DS17885 offers 8KB. All variants share similar core RTC functionalities and interface protocols.

Real Time Clock Replacement Considerations

Direct replacements include other members of the DS17x85 family such as the DS17285 or DS17885, depending on memory requirements. Legacy equivalents include the DS12887. Verify pinout compatibility and voltage levels when substituting.