BQ3285ESSTR

Overview

The BQ3285ESSTR is a CMOS real-time clock (RTC) and calendar IC from Texas Instruments, designed for IBM AT-compatible systems. It operates on a 4.5V to 5.5V supply with battery backup via the BC pin. The device provides timekeeping in seconds, minutes, hours, day of week, date, month, and year, supporting 12- or 24-hour formats and automatic leap-year adjustment. It includes 242 bytes of nonvolatile SRAM for general storage. Key features include three maskable interrupt sources (periodic, alarm, update-ended), a programmable square-wave output, and a dedicated 32.768kHz output for power management. The part is housed in a 24-pin SSOP package.

Feature Summary

• Multiplexed address/data bus interface compatible with Intel and Motorola architectures
• 242 bytes of general nonvolatile RAM for data storage
• Alarm wake-up capability active during battery-backup mode
• Battery operation current less than 0.5µA

Applications

• IBM AT-compatible computer systems
• Industrial control systems requiring precise timekeeping
• Data logging equipment with nonvolatile storage needs

Procurement Notes

This component is listed as obsolete by the manufacturer. Verification of availability should focus on authorized distributors offering surplus stock or alternative sourcing channels. Ensure the specific ESSTR suffix corresponds to the SSOP tape-and-reel packaging format required for surface-mount assembly processes.

Selection Notes

Select the BQ3285E variant for systems operating at 4.5V to 5.5V. The BQ3285L variant is required for 2.7V to 3.6V systems. Verify that the host processor supports the multiplexed bus timing selected via the MOT pin. Ensure the design accommodates an external 32.768kHz crystal with a 6pF load capacitance.

Part Context

The BQ3285ESSTR belongs to the bq3285E/L family of RTCs. It is functionally compatible with the DS1285 and closely matches the MC146818A pin configuration. The 'ESS' indicates the 24-SSOP package, while 'STR' denotes the reel packaging format. This series serves as a direct replacement for legacy RTCs in older PC architectures.

Replacement Considerations

Publicly confirmed substitute part numbers are not available in the provided documentation. Designers may consider the DS1285 or MC146818A for functional compatibility, though pinouts and electrical characteristics must be verified against the specific application requirements.