BQ3285ESTR

Overview

The BQ3285ESTR is a CMOS real-time clock (RTC) and calendar peripheral manufactured by Texas Instruments, designed for IBM AT-compatible systems. It operates within a supply voltage range of 4.5V to 5.5V and features a multiplexed address/data bus interface compatible with Intel or Motorola architectures. The device includes 14 bytes of clock/calendar registers and 242 bytes of general nonvolatile SRAM. Key specifications include a 32.768kHz oscillator input, battery backup support via the BC pin, and an operating temperature range of 0°C to +70°C. It provides alarm wake-up capabilities and programmable square-wave outputs.

Feature Summary

• Multiplexed bus interface supporting selectable Intel or Motorola timing protocols
• 242 bytes of general nonvolatile storage accessible via EXTRAM pin
• Alarm interrupt output active in battery-backup mode for system wake-up
• Programmable square-wave output ranging from 1Hz to 32.768kHz

Applications

• IBM AT-compatible computer systems
• Microprocessor peripheral timekeeping
• Battery-backed data logging applications

Procurement Notes

Verify component authenticity through authorized channels as this part may be subject to obsolescence. Confirm package type matches design requirements, as the EST suffix indicates a specific surface-mount variant. Ensure compatibility with existing bus timing configurations before integration into new designs.

Selection Notes

Select the bq3285E variant for 5V logic systems; the bq3285L is required for 3V operations. Verify that the host processor supports the multiplexed address/data bus cycle timing. Ensure external components, specifically the 32.768kHz crystal and backup battery, meet the specified load capacitance and voltage requirements for reliable operation.

Part Context

The BQ3285ESTR belongs to the bq3285E/L family of real-time clocks. It is functionally compatible with legacy devices such as the DS1285 and closely matches the MC146818A pin configuration. This family serves as a direct replacement for older RTC solutions in industrial and computing applications requiring precise timekeeping and nonvolatile storage.

Replacement Considerations

Publicly confirmed substitute part numbers are not available in the provided documentation. Designers should evaluate functional equivalents based on bus interface compatibility and voltage requirements.