DS1685SN-5

Real Time Clock Overview

The DS1685SN-5 is a real-time clock (RTC) IC from Analog Devices/Maxim Integrated, designed as a successor to the DS1287 standard. It operates at +5V and features a multiplexed address/data bus interface in a 24-pin SOIC package. The device provides timekeeping with Y2K compliance and leap-year correction through 2099. Key specifications include 242 bytes of battery-backed NV SRAM, a 64-bit silicon serial number, and power-control circuitry for system wake-up. It supports both 3V and 5V operation variants, with this specific model rated for 5V logic.

Real Time Clock Feature Summary

• Incorporates industry-standard DS1287 PC clock functions with enhanced Y2K compliance.
• Provides 242 bytes of battery-backed nonvolatile RAM accessible via multiplexed bus.
• Includes power-control circuitry allowing system power-on via date/time alarm or key closure.
• Features a 64-bit unique silicon serial number for identification.

Real Time Clock Applications

• Embedded systems requiring precise timekeeping.
• Utility meters needing nonvolatile data storage.
• Security systems with alarm logging capabilities.
• Network hubs, bridges, and routers for timestamping.

Real Time Clock Procurement Notes

Verify the specific suffix 'SN' corresponds to the SOIC package and '-5' indicates the 5V operating voltage variant. Confirm industrial temperature range requirements if applicable, as standard versions may differ from IND grades. Check current availability status as legacy RTC components may have limited stock or end-of-life notices from the manufacturer.

Real Time Clock Selection Notes

Select this component when compatibility with existing DS1287 BIOS implementations is required alongside enhanced features like kickstart functionality. Ensure the design accommodates the multiplexed bus timing constraints. Verify that the external crystal load capacitance matches the CS bit configuration (6pF or 12.5pF) for optimal accuracy.

Real Time Clock Part Context

The DS1685 series serves as an evolution of the Dallas Semiconductor DS1285/DS1287 line, now under Analog Devices/Maxim Integrated. It maintains pin-out compatibility while adding features such as auxiliary battery inputs and extended RAM access. The SN designation specifically identifies the surface-mount SOIC package variant within the broader DS1685 family.

Real Time Clock Replacement Considerations

Direct replacements include other DS1685 variants with matching voltage and package codes, such as DS1685S-5+ for commercial grade or DS1685SN-5+T&R for tape-and-reel packaging. Cross-reference tools should be used to verify parameter equivalence for specific industrial temperature ranges if required by the application.

Real Time Clock FAQ

How does the DS1685 handle power failure?

When VCC falls below the power-fail trip point, the device automatically switches to a backup supply connected to VBAT or VBAUX. Read/write operations are inhibited during this transition, but timekeeping and RAM retention continue uninterrupted.

What is the function of the KS pin?

The KS (Kickstart) pin allows the system to be powered on from a low-power state. When VCC is removed, an active-low transition on KS can trigger the PWR output to turn on the external power supply, provided the kickstart enable bit is set.

Can the DS1685 operate with a 3V battery if it is a 5V part?

Yes. While the DS1685SN-5 operates on a 5V primary supply (VCC), it supports backup power from a standard 3V lithium cell connected to VBAT or VBAUX. The backup voltage must remain between 2.5V and 3.7V for proper operation.