DS1643-100+

Real Time Clock Overview

The DS1643-100+ is a nonvolatile static RAM integrated with a real-time clock, crystal, and lithium energy source. It provides 8K x 8 byte-wide memory accessible via standard parallel interfaces (28-pin EDIP module). The device features BCD-coded timekeeping registers for year, month, date, day, hours, minutes, and seconds, including leap year compensation valid through 2100. Access times are specified at 85ns or 100ns depending on the variant. It includes power-fail write protection to prevent data corruption during voltage drops and maintains data retention for over 10 years using an internal lithium battery disconnected until first power application.

Real Time Clock Feature Summary

• Integrated NV SRAM, Real-Time Clock, Crystal, Power-Fail Control Circuit, and Lithium Energy Source
• BCD-Coded Year, Month, Date, Day, Hours, Minutes, and Seconds with Leap Year Compensation Valid Up to 2100
• Power-Fail Write Protection Allows for ±10% VCC Power Supply Tolerance
• Access Times of 85ns and 100ns

Real Time Clock Applications

• Systems requiring read/write nonvolatility in ROM/EPROM/EEPROM sockets
• Applications needing precise timekeeping with automatic calendar corrections
• Equipment requiring data retention during power outages without external battery management

Real Time Clock Procurement Notes

Verify the specific access time requirement (85ns vs 100ns) when ordering, as the datasheet lists both variants under the DS1643 family. Confirm the package type is the 28-pin EDIP module, as the DS1643P variant uses a different 34-pin PowerCap configuration. Ensure the system design accounts for the open-drain nature of the PFO and RST outputs, which require external pull-up resistors for proper operation.

Real Time Clock Selection Notes

Select the DS1643-100+ for through-hole applications requiring a compact, all-in-one solution with integrated timing components. This part is suitable for designs needing direct substitution for standard SRAMs while adding RTC functionality. Consider the operating temperature range of 0°C to +70°C and the 5V supply voltage requirements. For surface-mount applications, the DS1643P variant with a separate PowerCap should be evaluated instead.

Real Time Clock Part Context

The DS1643 series belongs to Maxim Integrated's line of nonvolatile timekeeping RAMs. The -100+ suffix indicates a lead-free/RoHS-compliant package version with 100ns access time. The device is functionally equivalent to JEDEC standard 8K x 8 SRAM but includes eight top locations reserved for double-buffered RTC registers. It was originally manufactured by Dallas Semiconductor before its acquisition by Maxim Integrated, now part of Analog Devices.

Real Time Clock Replacement Considerations

Publicly confirmed substitute part numbers are not available in the provided documentation. The DS1643 is pin-for-pin compatible with other densities of the DS164XP family, such as the DS1642 or DS1644, though storage capacities will differ. Verify compatibility with existing PCB footprints and software drivers designed for the DS1643 register map.

Real Time Clock FAQ

How does the DS1643 handle power failures?

The device includes internal power-fail circuitry that detects when VCC falls below the write protection voltage (VPF). At this point, access to the RAM and clock registers is blocked to prevent data corruption, and the device switches to the internal lithium battery for data retention.

What is the purpose of the double-buffered clock registers?

The double-buffered system prevents the reading of incorrect data during clock update cycles. It ensures that time accuracy is not affected by accessing time register data, as the internal clock continues to update while the user reads the buffered values.

How is the lithium battery activated?

Each DS1643 is shipped with the lithium energy source electrically disconnected. The battery is enabled for backup operation only when VCC is first applied at a level greater than the power-fail threshold (VPF).