DS1643-70

Real Time Clock Overview

The DS1643-70 is a nonvolatile timekeeping RAM integrating an 8K x 8 static RAM, real-time clock (RTC), crystal, and lithium energy source. It operates at 5V with access times of 85ns or 100ns. The RTC provides BCD-coded year, month, date, day, hours, minutes, and seconds with leap year compensation valid to 2100. Clock registers reside in the top eight RAM locations and are double-buffered. The device includes power-fail write protection and automatically switches to battery backup when VCC drops below the power-fail threshold.

Real Time Clock Feature Summary

• Integrated NV SRAM, RTC, crystal, and lithium battery
• BCD-coded timekeeping with automatic leap year correction
• Power-fail write protection for data integrity
• Double-buffered clock registers prevent read errors

Real Time Clock Applications

• Systems requiring persistent timekeeping during power loss
• Data logging applications needing nonvolatile storage
• Embedded controllers with standard JEDEC pinout compatibility

Real Time Clock Procurement Notes

Verify the specific speed grade suffix (-85 or -100) as the base model number does not specify access time. Confirm package type availability, as the DIP module integrates the battery while the PowerCap variant requires a separate component. Check RoHS compliance status indicated by the '+' suffix on ordering part numbers.

Real Time Clock Selection Notes

Select the DS1643 for through-hole applications using the integrated 28-pin EDIP module. Choose the DS1643P for surface-mount designs, ensuring the separate DS9034PCX PowerCap is ordered. Ensure system voltage remains within 4.5V to 5.5V for proper operation and write protection functionality.

Real Time Clock Part Context

The DS1643 belongs to the DS164XP family of nonvolatile timekeeping RAMs. It offers byte-wide interface compatibility with standard SRAMs. The device simplifies design by combining memory, timing, and power management functions into a single component, reducing board space and component count.

Real Time Clock Replacement Considerations

Pin-for-pin compatible with other densities in the DS164XP series. Verify access time requirements when substituting between -85 and -100 variants. Ensure replacement parts match the required package style (EDIP vs. PowerCap).

Real Time Clock FAQ

How is the lithium battery disconnected until first use?

A built-in switch electrically disconnects the lithium energy source until VCC is first applied above the power-fail threshold.

What happens if VCC drops below the power-fail point?

The device enters data retention mode, blocking access via CE and switching power to the internal battery to maintain clock and RAM data.

How accurate is the real-time clock?

The DIP module guarantees accuracy within ±1 minute per month at 25°C. The PowerCap module guarantees accuracy within ±1.53 minutes per month at 25°C.