BQ4845S-A4

Overview

The BQ4845S-A4N is a low-power microprocessor peripheral integrating a real-time clock, 100-year calendar, and CPU supervisor in a 28-pin SOIC package. It operates on a +5V supply (4.75V to 5.5V) with a parallel interface for direct connection to system data buses. The device features an on-chip battery-backup switchover circuit that maintains timekeeping and external SRAM data using a 3V backup cell. Key electrical parameters include less than 500nA current consumption in backup mode and a power-fail interrupt warning. It includes a programmable watchdog timer and supports alarm and periodic interrupts.

Feature Summary

• Integrates a real-time clock counting seconds through years in BCD format with automatic leap year adjustment.
• Includes a nonvolatile control circuit for external SRAM write-protection during power failures via CEOUT and VOUT pins.
• Features an independent watchdog timer with programmable time-out periods ranging from 1.5s to 3s.
• Provides power-fail interrupt warnings and a microprocessor reset signal valid down to VSS.

Applications

• Fax machines
• Copiers
• Industrial control systems
• Point-of-sale terminals
• Data loggers

Procurement Notes

Verify the specific suffix 'A4N' against the manufacturer's official documentation, as standard variants are designated by 'P' (DIP) or 'S' (SOIC) with temperature codes like 'N'. Confirm availability status, as this component may be discontinued or subject to obsolescence notices. Ensure the ordering information matches the required voltage tolerance and operating temperature range specified in the latest datasheet.

Selection Notes

Select the BQ4845S variant for surface-mount applications requiring a 28-pin SOIC package. Ensure the design accommodates a 32.768kHz crystal connected to X1/X2 pins and a 3V backup battery on the BC pin. Verify that the host microprocessor can support the parallel interface timing requirements, including chip select and output enable signals. Check if the industrial temperature range (-40°C to +85°C) is required, which corresponds to the 'N' suffix.

Part Context

The bq4845 belongs to Texas Instruments' family of parallel RTCs with CPU supervisors. It is functionally similar to the bq4847 but offers a different memory interface configuration. The device serves as a bridge between the microprocessor and external nonvolatile memory, ensuring data integrity during power transitions. It replaces older discrete clock and supervisor solutions by integrating these functions into a single IC.

Replacement Considerations

Publicly confirmed substitute part numbers for the BQ4845S-A4N are not available in the provided source material. Users should consult the manufacturer's official obsolescence notices or cross-reference guides for equivalent components with compatible pinouts and functionality.