BQ3285P-SB2E3

Overview

The Texas Instruments BQ3285P-SB2E3 is a CMOS real-time clock (RTC) peripheral designed for IBM AT-compatible systems. It provides time-of-day, a 100-year calendar with automatic leap-year adjustment, and alarm features. The device includes 114 bytes of general nonvolatile storage and three individually maskable interrupt sources. It operates on a +5V supply with less than 0.5μA load under battery operation. Key electrical parameters include a 160ns cycle time, 32.768kHz crystal input, and backup cell voltage range of 2.5V to 4.0V. Operating temperature is specified from 0°C to +70°C.

Feature Summary

• Direct replacement for DS1285 with MC146818A pin compatibility
• 114 bytes of general nonvolatile storage plus 14 bytes for clock/control
• Selectable Intel or Motorola bus timing via MOT pin
• Three maskable interrupts: periodic, alarm, and update-ended

Applications

• IBM AT-compatible computer systems
• Microprocessor peripherals requiring time-of-day and calendar
• Applications needing low-power battery-backed nonvolatile storage

Procurement Notes

Verify the package type matches the required form factor, as the BQ3285 is available in 24-pin DIP (P) and SOIC (S). Confirm that the commercial temperature grade (0°C to +70°C) meets system requirements. Ensure the design accounts for the specific bus timing signals (AS, DS, R/W) based on the selected Intel or Motorola architecture configuration.

Selection Notes

Select the BQ3285P-SB2E3 when a direct functional equivalent to the DS1285 is needed for legacy PC architectures. Choose this component if the application requires selectable bus timing for either Intel or Motorola processors. Ensure the design supports a 32.768kHz crystal with 6pF load capacitance and provides a 3V backup cell connection for data retention during power failures.

Part Context

The BQ3285 is part of Texas Instruments' RTC family, functionally compatible with National Semiconductor's DS1285. It serves as a microprocessor peripheral for maintaining accurate timekeeping and calendar data in systems requiring nonvolatile storage. The device integrates oscillator control, frequency division, and interrupt generation logic into a single CMOS chip.

Replacement Considerations

The BQ3285 is functionally compatible with the DS1285 and closely matches the MC146818A pin configuration. Verify that the host system's bus timing aligns with the chosen MOT pin setting before substitution.