BQ3285LDSSTR

Overview

The BQ3285LDSSTR is a low-power CMOS real-time clock (RTC) module manufactured by Texas Instruments, designed for direct replacement in IBM AT-compatible systems. It operates within a supply voltage range of 2.7V to 3.6V and features a multiplexed address/data bus interface compatible with Intel or Motorola architectures. The device integrates a 100-year calendar with automatic leap-year adjustment, time-of-day tracking, and three individually maskable interrupt sources: periodic, alarm, and update-ended. It provides 242 bytes of general nonvolatile SRAM storage and includes a programmable square-wave output. The component is housed in a 24-pin SSOP package.

Feature Summary

• Low-power operation at 2.7–3.6V with less than 0.5μA battery load
• 242 bytes of general nonvolatile storage plus 14 bytes of clock/calendar registers
• Alarm interrupt capability active in battery-backup mode for system wake-up
• Selectable Intel or Motorola bus timing via the MOT pin

Applications

• IBM AT-compatible computer systems
• Battery-backed real-time clock modules
• Systems requiring low-power calendar and timer functions

Procurement Notes

Verify that the design supports the 2.7–3.6V operating voltage range specific to the bq3285L variant. Ensure the backup battery circuit connects to the BC pin to maintain data integrity during power failures. Confirm that the host processor interface matches the multiplexed bus timing requirements for either Intel or Motorola modes as selected by the MOT pin configuration.

Selection Notes

Select the bq3285L variant specifically for 3V system applications, as the bq3285E variant requires 4.5–5.5V. The DSSTR suffix indicates a tape-and-reel packaging format suitable for automated surface-mount assembly. Verify compatibility with external 32.768kHz crystals having a 6pF load capacitance requirement for accurate timekeeping.

Part Context

This component belongs to the bq3285E/L family of real-time clocks from Texas Instruments. It is functionally compatible with the National Semiconductor DS1285 and closely matches the pin configuration of the MC146818A. The bq3285L series is distinguished by its lower voltage operation capabilities compared to the standard bq3285E series.

Replacement Considerations

Functionally compatible replacements include the DS1285 and MC146818A, provided voltage levels and bus timing configurations are adapted. Ensure any substitute part supports the required 242-byte nonvolatile storage capacity and battery-backed alarm interrupt functionality.