DS1557WP-120+

Real Time Clock Overview

The DS1557WP-120+ is a nonvolatile, Y2K-compliant timekeeping RAM integrating a real-time clock (RTC), static RAM, and lithium energy source. It features 512k x 8 SRAM with a byte-wide parallel interface. The RTC provides century, year, month, date, day, hours, minutes, and seconds in BCD format with automatic leap-year compensation up to 2100. Operating at 3.3V ±10%, it maintains data for over 10 years without power. Key functions include a programmable watchdog timer, alarm, power-fail write protection, and battery voltage monitoring.

Real Time Clock Feature Summary

• Integrated NV SRAM, RTC, crystal, power-fail control, and internal lithium battery
• Y2K compliant with automatic leap-year compensation valid through 2100
• Programmable watchdog timer and RTC alarm with interrupt output
• Power-fail write protection ensures data security during supply fluctuations

Real Time Clock Applications

• Industrial systems requiring precise timekeeping and nonvolatile storage
• Embedded controllers needing backup memory and system reset capabilities
• Battery-powered devices requiring low standby current and long retention

Real Time Clock Procurement Notes

Verify the specific suffix indicates the 3.3V commercial temperature grade (0°C to +70°C). Confirm that the required PowerCap module base (DS9034PCX+) is ordered separately as it is not included with the IC. Ensure the design accounts for the open-drain nature of the IRQ/FT and RST outputs requiring external pull-up resistors.

Real Time Clock Selection Notes

Select this component when a combined RTC and large NVSRAM solution is needed in a single package. Compare against the 5V variant if system supplies differ. Note that the industrial version (-40°C to +85°C) is designated by the 'IND' suffix. Verify board layout constraints for the 34-pin PowerCap module footprint and land pattern.

Real Time Clock Part Context

This device belongs to the DS1557 family of timekeeping RAMs. It is functionally similar to the DS1556 but offers higher memory density (512KB vs 128KB) and uses a 34-pin PowerCap package instead of a standard DIP. It serves as a drop-in replacement for older discrete RTC and SRAM combinations in legacy designs.

Real Time Clock Replacement Considerations

Direct pin-compatible substitutes within the same package include other DS1557 variants with different speed or temperature ratings. Cross-family replacements like the DS12887 require significant schematic changes due to multiplexed interfaces and different pinouts.