BQ4845YS-A4

Overview

The BQ4845YS-A4 is a low-power microprocessor peripheral integrating a real-time clock, 100-year calendar, and CPU supervisor in a 28-pin SOIC package. It features a parallel interface with 16 bytes of nonvolatile control for external SRAM. The device operates on a +5V supply (4.75V to 5.5V) with less than 500nA current in battery-backup mode. Key functions include an independent watchdog timer, power-fail interrupt, programmable periodic and alarm interrupts, and automatic leap year adjustment.

Feature Summary

• Integrates RTC, 100-year calendar, and CPU supervisor in a single 28-pin SOIC component
• On-chip battery-backup switchover circuit maintains external SRAM data during power loss
• Independent watchdog timer with programmable time-out periods ranging from 30.5μs to 3 seconds
• Programmable clock alarm and periodic interrupts active in battery-backup mode

Applications

• Fax machines and copiers requiring precise timing and memory retention
• Industrial control systems needing CPU supervision and watchdog monitoring
• Point-of-sale terminals and data loggers utilizing nonvolatile RAM backup
• Computers and embedded systems requiring parallel RTC interfaces

Procurement Notes

Verify the specific suffix 'A4' against the official Texas Instruments datasheet to confirm temperature range and voltage tolerance specifications. Confirm that the 28-pin SOIC package dimensions match the design footprint requirements. Ensure compatibility with the 3V backup battery input on the BC pin for proper oscillator start-up and data retention.

Selection Notes

Select this component when a parallel interface is required for direct connection to standard SRAM buses. The bq4845Y variant offers a 10% voltage tolerance compared to the 5% tolerance of the standard bq4845. Consider the industrial temperature range (-40°C to +85°C) if operating in harsh environments. Ensure the system design accommodates the open-drain outputs for RST, INT, and WDO pins requiring external pull-up resistors.

Part Context

The bq4845 series serves as a comprehensive timing and supervision solution for microprocessor-based systems. It combines timekeeping with critical system protection features like power-fail detection and watchdog monitoring. The device simplifies board design by eliminating the need for separate supervisor ICs and dedicated battery-backed RAM controllers, consolidating these functions into a single parallel-accessible chip.

Replacement Considerations

Public confirmed substitute part numbers are not available in the provided documentation.