BQ4845S-A4NTR

Overview

The BQ4845S-A4NTR is a low-power parallel real-time clock (RTC) with CPU supervisor, manufactured by Texas Instruments. It integrates a time-of-day clock, a 100-year calendar, and a watchdog timer in a 28-pin SOIC package. The device operates on a +5V supply (4.75V to 5.5V) with less than 500nA current in battery-backup mode. It features nonvolatile control for external SRAM via conditional chip enable and backup battery output pins. Key functions include programmable periodic and alarm interrupts, power-fail detection, and microprocessor reset generation.

Feature Summary

• Integrates RTC, 100-year calendar, and CPU supervisor in a single 28-pin component
• Provides on-chip battery-backup switchover circuit with nonvolatile control for external SRAM
• Includes independent watchdog timer with programmable time-out periods from 30.5μs to 3s
• Generates interrupts for power-fail, periodic events, and alarms, with alarm capability active in battery-backup mode

Applications

• Fax machines and copiers requiring precise timing and system supervision
• Industrial control systems needing reliable clock and memory retention
• Point-of-sale terminals and data loggers with battery-backed memory requirements
• Computers and embedded systems utilizing parallel interface peripherals

Procurement Notes

Verify the 'TR' suffix indicates tape-and-reel packaging when sourcing this specific variant. Confirm the 'S' designation corresponds to the 28-pin SOIC package and 'N' indicates the industrial temperature range (-40°C to +85°C). Ensure compatibility with existing parallel bus designs, as this component replaces standard discrete RTC and supervisor circuits.

Selection Notes

Select this part for applications requiring a parallel interface RTC with integrated CPU supervision. It is suitable where low standby current and external SRAM write-protection are critical. Compare against the BQ4845Y series if 10% voltage tolerance is acceptable instead of the stricter 5% tolerance of the base model. Ensure the design accommodates the 28-pin SOIC footprint and provides connections for a 32.768kHz crystal and 3V backup battery.

Part Context

This component belongs to the bq4845 family of real-time clocks. The 'S' indicates the SOIC package, while 'N' specifies the industrial temperature grade. It serves as a direct replacement for older discrete RTC and supervisor solutions in legacy parallel bus architectures. The device simplifies board design by combining timekeeping, calendar calculation, and power management supervision into one IC.

Replacement Considerations

Direct pin-compatible replacements within the same package and temperature range should be verified against the latest TI product selection guide. Note that newer alternatives may offer serial interfaces (I2C/SPI) rather than parallel, requiring significant schematic redesign. Check for any obsolescence notices or PCNs affecting the bq4845 series.