DS1685, DS1687 3V/5V Real-Time Clock

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The DS1685/DS1687 are real-time clocks (RTCs) designed as successors to the industry-standard DS1285,DS1385, DS1485, and DS1585 PC RTCs. These devices provide the industry-standard DS1285 clock function with either +3.0V or +5.0V operation. The DS1685 also incorporates a number of enhanced features including a silicon serial number, power-on/off control circuitry, 242 bytes of user NV SRAM, and 32.768kHz output for sustaining power management activities.

The DS1685/DS1687 power-control circuitry allows the system to be powered on by an external stimulus such as a keyboard or by a time and date (wake-up) alarm. The PWR output pin can be triggered by one or either of these events, and can be used to turn on an external power supply. The PWR pin is under software control, so that when a task is complete, the system power can then be shut down.

The DS1685 is a clock/calendar chip with the features described above. An external crystal and battery are the only components required to maintain time-of-day and memory status in the absence of power. The DS1687 incorporates the DS1685 chip, a 32.768kHz crystal, and a lithium battery in a complete, self-contained timekeeping EDIP. The entire unit is fully tested at Dallas Semiconductor such that a minimum of 10 years of timekeeping and data retention in the absence of V_CC is guaranteed.

Key Features

Applications/Uses

Incorporates Industry-Standard DS1287 PC Clock plus Enhanced Features Such as:

Y2K Compliant
+3V or +5V Operation
64-Bit Silicon Serial Number
Power-Control Circuitry Supports System Power-On from Date/Time Alarm or Key Closure
32kHz Output for Power Management
Crystal-Select Bit Allows RTC to Operate with 6pF or 12.5pF Crystal
SMI Recovery Stack
242 Bytes Battery-Backed NV RAM
Auxiliary Battery Input
RAM Clear Input
Century Register
Date Alarm Register
Compatible with Existing BIOS for Original DS1287 Functions
Available as Chip (DS1685) or Stand-Alone Encapsulated DIP (EDIP) with Embedded Battery and Crystal (DS1687)
Timekeeping Algorithm Includes Leap-Year Compensation Valid Through 2099
Underwriters Laboratory (UL) Recognized

	Embedded Systems
	Network Hubs, Switches, Routers
	Security Systems
	Utility Meters

Key Specifications: Timekeeping & Real-Time Clocks

Part Number

Time Format (hh = sec/100)

Date Format

Interface

Supply Voltage (V)

Time- keeping Current (typ) (nA)

C_L, Load Capacitance (pF)

Memory Type

Memory Size (Bytes)

Number of Time of Day Alarms

Features

RoHS Available

Package

Smallest Available Package (max w/pins) (mm²)

Operating Temp. Range (°C)

Price^**

DS1685

HH:MM:SS

YYYY-MM-DD

Multiplexed

3
5

400

12.5
6

NV SRAM

242

•	Kick-Start

•	Periodic Interrupt

•	RAM Clear Interrupt

•	Serial Number

•	Square-Wave Output

•

Wake-up

Yes

PDIP/24
PLCC/28
SOIC/24
TSSOP/24

-40 to +85

$2.52 @ 1k

DS1687

•	Battery + Crystal

•	Kick-Start

•	Periodic Interrupt

•	RAM Clear Interrupt

•	Serial Number

•	Square-Wave Output

•

Wake-up

MOD/24

640

$4.43 @ 1k

See All Timekeeping & Real-Time Clocks (86)

Notes:
^**This pricing is BUDGETARY, for comparing similar parts. Prices are in U.S. dollars and subject to change. Quantity pricing may vary substantially and international prices may differ due to local duties, taxes, fees, and exchange rates. For volume-specific prices and delivery, please see the price and availability page or contact an authorized distributor.