DS1642-70+

Real Time Clock Overview

The DS1642-70+ is a nonvolatile timekeeping RAM integrating a real-time clock (RTC) and static RAM in a single package. It features a standard JEDEC bytewide 2k x 8 SRAM pinout with an access time of 70ns. The device operates at a supply voltage of 5.0V within a temperature range of 0°C to +70°C, housed in a 24-pin EDIP package. Clock registers reside in the top eight RAM locations, providing BCD-coded year, month, date, day, hours, minutes, and seconds with leap year compensation valid up to 2100. The unit includes an integrated lithium energy source for over 10 years of data retention without power.

Real Time Clock Feature Summary

• Integrated NV SRAM, RTC, crystal, power-fail control circuit, and lithium battery
• Standard JEDEC 2k x 8 static RAM pinout compatibility
• BCD-coded timekeeping with automatic leap year correction valid to 2100
• Power-fail write protection ensures data integrity during voltage fluctuations

Real Time Clock Applications

• System controllers requiring persistent time and data storage
• Replacement for ROM, EPROM, or EEPROM sockets with added RTC functionality
• Industrial equipment needing reliable timekeeping under variable power conditions

Real Time Clock Procurement Notes

Verify component authenticity through authorized distributors. Confirm that the ordering suffix '+' indicates lead-free status. Ensure the specific -70 speed grade matches system timing requirements. Check for RoHS compliance documentation if required by local regulations. Note that the internal lithium source is disconnected until initial power application.

Real Time Clock Selection Notes

Select the DS1642-70+ when a 70ns access time is required for the 0°C to +70°C commercial temperature range. Choose the -100 variant if slower access times are acceptable but lower power consumption is desired. Ensure the design accommodates the 24-pin EDIP package dimensions. Verify that the system VCC tolerance aligns with the internal power-fail threshold of approximately 4.37V.

Real Time Clock Part Context

This component belongs to the Maxim Integrated DS1642 family of nonvolatile timekeeping RAMs. It serves as a direct pin-compatible replacement for standard 2k x 8 SRAMs while adding calendar and clock functions. The device simplifies system design by eliminating external components typically required for RTC and battery backup circuits.

Real Time Clock Replacement Considerations

Direct substitutes include other parts from the DS1642 family such as the DS1642-100+ for slower access speeds. Cross-family replacements require careful verification of pinouts, voltage levels, and register maps to ensure functional equivalence in existing PCB layouts.

Real Time Clock FAQ

How is the internal lithium battery activated?

The lithium energy source is electrically disconnected upon shipment to preserve freshness. It is automatically enabled for battery backup operation only when VCC is first applied at a level greater than the power-fail point (VPF).

What is the accuracy of the real-time clock?

The DS1642 is factory calibrated to maintain time accuracy within ±1 minute per month at +25°C. Field calibration is not necessary or available due to negligible effects from temperature deviations in most applications.

How does the device handle power failures?

An internal power-fail circuitry detects when VCC falls below the write protection voltage (VPF). This action deselects the device, preventing unpredictable system operations and ensuring data loss does not occur during low voltage conditions.