3 Volt/5 Volt Serialized Real-Time Clock with NV RAM Control

Overview

Technical Documents

Ordering Info

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Status

Part Number	Status	Replacement	Explanation
DS1688	This product is No Longer Available. See Ordering Information for recommended replacements.	DS1685 DS17285 DS17485 DS17885	There is no direct replacement. The DS17x85 has 2K, 4K, and 8K bytes extended RAM.
DS1691	This product is No Longer Available. See Ordering Information for recommended replacements.	DS1685 DS17285 DS17485 DS17885	There is no direct replacement. The DS17x85 has 2K, 4K, and 8K bytes extended RAM.

Description

The DS1688/DS1691 is a real-time clock (RTC) designed as a successor to the industry standard DS1285, DS1385, DS1485, and DS1585 PC real time clocks. This device provides the industry standard DS1285 clock function with the new feature of either +3.0 or +5.0V operation and automatic backup and write protection to an external SRAM. The DS1688 also incorporates a number of enhanced features including a silicon serial number, power on/off control circuitry, 114 bytes of user NV SRAM, power on elapsed timer, and power cycle counter.

Data Sheet

Download	Rev 2	(PDF, 100kB)
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This product contains lithium-metal batteries. See applicable regulations for transport requirements for batteries in equipment.

Key Features

Incorporates industry standard DS1287 PC clock plus enhanced features:

+3 or +5V operation
64-bit Silicon serial number
64-bit customer specific ROM or additional serial number available
Power control circuitry supports system power on from date/time alarm or key closure
Automatic battery backup and write protection to external SRAM
Crystal select bit allows RTC to operate with
6pF or 12.5pF crystal
114 bytes user NV RAM
Auxiliary battery input
RAM clear input
Century register
32kHz output for power management
32-bit V_CC powered elapsed time counter
32-bit V_BAT powered elapsed time counter
16-bit power cycle counter
Compatible with existing BIOS for original DS1287 functions
Available as IC (DS1688) or stand-alone module with embedded battery and crystal (DS1691)
Timekeeping algorithm includes leap year compensation valid up to 2100
Underwriters Laboratories (UL) Recognized

Application Notes

Application Note 58		Crystal Considerations with Maxim Real-Time Clocks (RTCs)
Application Note 499		Using the Multiplex Bus RTC Extended Features
Application Note 701		Using the DS32kHz with Dallas Real-Time Clocks
Application Note 3778		Problems and Solutions for Adjusting to Changes in Daylight Saving Time

Product Guides

Real-Time Clocks (PDF)

Reliability Reports

Reliability Report:	DS1688.pdf DS1691.pdf
Underwriters Laboratories (UL) Recognized

Software/Models

none

Ordering Information

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Tape and Reel

Sample

Part Number	Free Sample	Buy	Status	Recommended Replacement	Package: TYPE PINS FOOTPRINT DRAWING CODE/VAR *	Temp	RoHS/Lead-Free? Materials Analysis
DS1688		N/A	No Longer Available	DS1685-5+ There is no direct replacement. The DS17x85 has 2K, 4K, and 8K bytes extended RAM.	PDIP(W);28 pin;592.6 mm² Outline Drawing:21-0044 (PDF) Land Pattern: Not Applicable Use pkgcode/variation: P28-3*	0°C to +70°C	RoHS/Lead-Free: No Materials Analysis
DS1688S		N/A	No Longer Available	DS1685S-5+	SOIC(W);28 pin;235 mm² Outline Drawing:21-0251 (PDF) Land Pattern: 90-0255 (PDF) Use pkgcode/variation: F28-2*	0°C to +70°C	RoHS/Lead-Free: No Materials Analysis
DS1688S+		N/A	No Longer Available	DS1685S-5+	SOIC(W);28 pin;235 mm² Outline Drawing:21-0251 (PDF) Land Pattern: 90-0255 (PDF) Use pkgcode/variation: F28+2*	0°C to +70°C	RoHS/Lead-Free: Lead Free Materials Analysis
DS1691		N/A	No Longer Available	DS1687-5+ There is no direct replacement. The DS17x85 has 2K, 4K, and 8K bytes extended RAM.	EDIP;28 pin;625.9 mm² Outline Drawing:21-0241 (PDF) Land Pattern: Not Available Use pkgcode/variation: MDP28-2*	0°C to +70°C	RoHS/Lead-Free: No Materials Analysis

Notes:

Other options and links for purchasing parts are listed at: http://www.maxim-ic.com/sales.
Didn't Find What You Need? Ask our applications engineers. Expert assistance in finding parts, usually within one business day.
Part number suffixes: T or T&R = tape and reel; + = RoHS/lead-free; # = RoHS/lead-exempt; -D = drypack; -U/+U on DS parts = cut tape. More: See Full Data Sheet or Maxim Product Naming Conventions.
* Some packages have variations, listed on the drawing. "PkgCode/Variation" tells which variation the product uses. Note that "+", "#", "-" in the part number suffix describes RoHS status. Package drawings may show a different suffix character.

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Rev 2; 2005-11-28
This page last modified: 2009-06-04