BQ4845YS-A4N

Overview

The BQ4845YS-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 characteristics 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 CPU supervisor with a power-on reset valid to VSS and an independent watchdog timer with programmable time-out periods.
• Features an on-chip battery-backup switchover circuit with nonvolatile control for external SRAM via CEOUT and VOUT pins.
• Provides multiple interrupt capabilities including power-fail warning, programmable clock alarm, and periodic interrupt.

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 ordering information, as standard documentation lists 'N' for industrial temperature range and 'S' for SOIC packaging. Confirm availability status, as this component may be discontinued or subject to last-time buy restrictions. Ensure the selected package matches the design requirements, as the datasheet specifies both DIP and SOIC options for the base model.

Selection Notes

Select the BQ4845YS-A4N for applications requiring a parallel interface RTC with integrated CPU supervision. The 'Y' suffix indicates a 10% voltage tolerance compared to the 5% tolerance of the standard bq4845. The 'S' designation confirms the 28-pin SOIC package. Ensure the design accommodates the required 32.768kHz crystal and 3V backup battery connections. Verify that the parallel bus timing requirements align with the host microprocessor specifications.

Part Context

The bq4845 series serves as a comprehensive solution for maintaining system time and supervising processor operations in embedded environments. The bq4845YS variant specifically offers relaxed voltage tolerance specifications suitable for general-purpose commercial and industrial applications. The integration of SRAM control logic simplifies system design by reducing the component count required for nonvolatile memory management during power transitions.

Replacement Considerations

Direct pin-compatible replacements within the same family include the bq4845P-A4N (DIP package) and bq4845YP-A4N. For different packages, the bq4845S-A4N provides the same functionality in the SOIC form factor. Cross-voltage tolerance variants such as the bq4845S-A4 (5% tolerance) are functionally identical but differ in supply voltage specifications.