BQ3285S-SB2TRG4

Overview

The Texas Instruments bq3285 is a CMOS real-time clock (RTC) peripheral providing time-of-day, a 100-year calendar with automatic leap-year adjustment, and alarm features. It includes 114 bytes of general nonvolatile storage and three individually maskable interrupt sources. The device operates on a +5V supply with less than 0.5μA load under battery operation. Key electrical parameters include a 160ns cycle time, 4.5V to 5.5V supply voltage range, and an operating temperature of 0°C to +70°C. It requires only a 32.768kHz crystal and a backup battery as external components.

Feature Summary

• Direct replacement for IBM AT-compatible computers with functional compatibility to DS1285 and MC146818A pin configurations.
• Provides 114 bytes of general nonvolatile storage and 14 bytes for clock/calendar and control registers.
• Supports selectable Intel or Motorola bus timing via the MOT pin.
• Features programmable square wave output and three maskable interrupts: periodic, time-of-day alarm, and end-of-clock update.

Applications

• IBM AT-compatible computer systems
• Microprocessor peripherals requiring low-power timekeeping
• Applications necessitating nonvolatile data storage during power failures

Procurement Notes

Verify package availability as the datasheet notes the PLCC option reached Last Time Buy in May 2004. Confirm the specific suffix requirements for commercial temperature grade (0 to +70°C) and ensure the ordering code matches the desired DIP or SOIC configuration. Check current production status directly with Texas Instruments as product discontinuations may occur without notice.

Selection Notes

Select the bq3285 when a fully compatible RTC for legacy IBM AT systems is required. Ensure the design supports a +5V logic interface and accommodates the 24-pin DIP or SOIC footprint. Verify that the system can provide a 3V backup cell connection to the BC pin for maintaining data integrity during power loss. Consider the 160ns cycle time for high-speed bus integration.

Part Context

The bq3285 is part of Texas Instruments' legacy real-time clock family designed for microprocessor-based systems. It serves as a direct functional equivalent to the Dallas Semiconductor DS1285. The component integrates oscillator control, frequency division, and write-protection circuitry to maintain accurate timekeeping and data retention independently of the main system power.

Replacement Considerations

The bq3285 is functionally compatible with the DS1285 and closely matches the MC146818A pin configuration. Designers replacing existing components should verify pin-to-pin compatibility and bus timing settings (Intel vs. Motorola) to ensure seamless integration without schematic modifications.