BQ3285LFSS-A1

Overview

The BQ3285LFSS-A1 is a CMOS real-time clock (RTC) and calendar IC from Texas Instruments, housed in a 24-pin SSOP package. It operates on a supply voltage of 2.7V to 5.5V with battery backup support between 2.4V and 4V. The device provides time-of-day tracking, a 100-year calendar with Y2K compliance, and alarm features. It includes 242 bytes of nonvolatile static RAM for general storage. Key electrical characteristics include a typical standby current of 100µA at 3V and less than 0.55µA during battery operation. The component supports both Intel and Motorola bus timing protocols.

Feature Summary

• ACPI-compliant day-of-month alarm and Y2K century bit support
• 240 bytes of general nonvolatile SRAM storage
• Dedicated 32.768kHz output pin for power management
• System wake-up capability via alarm interrupt in battery-backup mode

Applications

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

Procurement Notes

Verify the component status as discontinued by Texas Instruments. Confirm availability through authorized distributors or secondary market suppliers such as Rochester Electronics. Ensure the 24-SSOP package variant matches the design requirements. Check RoHS3 compliance status for environmental regulations. Validate that the specific ordering suffix corresponds to the required temperature range and packaging format.

Selection Notes

Select this RTC for systems requiring direct replacement for legacy IBM AT architectures. Ensure the host processor supports parallel interface timing compatible with either Intel or Motorola standards. Verify that the system can provide a stable 32.768kHz crystal load capacitance of 6pF. Confirm that the available backup battery voltage falls within the 2.4V to 4V range for proper switch-over functionality.

Part Context

This part belongs to the bq3285 family of real-time clocks. The LF suffix indicates enhanced features compared to the base bq3285, including low-voltage operation, a dedicated 32kHz output, and additional SRAM bytes. The SS designation specifies the 24-pin plastic small-outline shrink package. The -A1 suffix typically denotes a specific revision or manufacturing lot code within the TI product line.

Replacement Considerations

Public confirmed substitute part numbers are not provided in the source material. Due to the discontinued status, verify pin compatibility and register mapping carefully when selecting alternative RTCs from other manufacturers. Ensure functional equivalence regarding bus timing and interrupt handling.