BQ4285LS

Overview

The Texas Instruments bq4285LS is a low-power CMOS microprocessor peripheral providing time-of-day clock, 100-year calendar, and 114 bytes of general nonvolatile storage. It operates within a 2.7V to 3.6V supply range and features automatic backup control for external SRAM during power failures. The device includes three individually maskable interrupt sources: periodic, alarm, and update-ended. It supports BCD or binary data formats, daylight saving adjustments, and a programmable square-wave output. The component requires only an external 32.768kHz crystal and a backup battery for operation.

Feature Summary

• Direct replacement for IBM AT-compatible computer RTCs with 114 bytes of NVRAM
• Automatic write-protect and backup controller for external SRAM
• Alarm interrupt active in battery-backup mode for system wake-up
• Programmable square-wave output including 32.768kHz option

Applications

• IBM AT-compatible computers
• Microprocessor peripheral systems requiring real-time clock
• Battery-backed storage applications

Procurement Notes

Verify the specific suffix 'S' against the official datasheet to confirm package type and temperature rating, as the source document primarily details the standard 'L' variant. Ensure the design utilizes a 3V backup cell on the BC pin for proper voltage switching. Confirm that the host system interface matches the multiplexed address/data bus requirements.

Selection Notes

Select this model for applications requiring a 2.7V to 3.6V operating voltage. The bq4285E variant is required if the system operates at 4.5V to 5.5V. Ensure the design accommodates the 24-pin DIP or SOIC package. Verify compatibility with Intel architecture bus timing if MOT pin configuration is not adjusted.

Part Context

The bq4285E/L series serves as a fully compatible real-time clock for IBM AT-compatible computers. It integrates a battery-backup controller to maintain CMOS SRAM nonvolatility during power-fail conditions. The device functions as a low-power microprocessor peripheral, eliminating the need for complex external logic for backup management.

Replacement Considerations

The datasheet confirms functional compatibility with the DS1285. When substituting, ensure the replacement supports the same multiplexed address/data bus interface and 24-pin package form factor.