DS1643-85+

Real Time Clock Overview

The DS1643-85+ is a nonvolatile timekeeping RAM integrating an 8K x 8 static RAM, real-time clock (RTC), crystal, and lithium energy source in a 28-pin EDIP module. It provides byte-wide access identical to standard SRAM, with RTC registers located in the top eight memory locations. The device features BCD-coded timekeeping with leap year compensation valid through 2100. Key electrical parameters include an 85ns access time, a 5.0V nominal supply voltage (4.5V to 5.5V range), and CMOS standby current of 3mA maximum. It includes power-fail write protection and automatic data retention switching to the internal battery upon VCC loss.

Real Time Clock Feature Summary

• Integrated NV SRAM, RTC, Crystal, and Lithium Battery in a single 28-pin EDIP package
• Standard JEDEC Byte-Wide 8K x 8 RAM interface with 85ns access time
• BCD-Coded Calendar/Clock with Leap Year Compensation valid up to 2100
• Power-Fail Write Protection ensures data integrity during ±10% VCC tolerance

Real Time Clock Applications

• Systems requiring nonvolatile timekeeping and data storage in a compact DIP form factor
• Replacement for ROM/EPROM sockets providing read/write nonvolatility
• Industrial or commercial equipment needing battery-backed memory without external components

Real Time Clock Procurement Notes

Verify that the specific order quantity matches the factory pack quantity of 12 units per tube. Confirm that the application environment remains within the specified operating temperature range of 0°C to +70°C. Ensure the system design accommodates the 28-pin EDIP footprint and handles the open-drain Power-Fail output requirements correctly.

Real Time Clock Selection Notes

Select the DS1643-85+ when a through-hole DIP solution is required for direct integration of the battery and crystal. Choose this part over the DS1643P variant if surface-mount technology is not mandated. The -85 suffix denotes the 85ns speed grade; verify timing constraints against the system bus requirements before finalizing the selection.

Real Time Clock Part Context

This component belongs to the DS164XP family of nonvolatile timekeeping RAMs. It is functionally equivalent to other densities in the series but offers a specific 8K x 8 capacity. The device is manufactured by Maxim Integrated (now Analog Devices) and is designed to simplify PCB layout by eliminating the need for separate battery holders and crystals.

Real Time Clock Replacement Considerations

Pin-for-pin compatible with other densities of the DS164XP series. Verify that any substitute maintains the same 28-pin EDIP package and 85ns access speed. Ensure the replacement supports the same BCD time format and power-fail voltage thresholds.