BQ4845

RTC IC W NVSRAM 控制器、看门狗定时器、加电复位、中断与低电池电量警告

The bq4845 Real-Time Clock is a low-power microprocessor peripheral that integrates a time-of-day clock, a 100-year calendar, and a CPU supervisor in a 28-pin SOIC or DIP. The bq4845 is ideal for fax machines, copiers, industrial control systems, point-of-sale terminals, data loggers, and computers.

The bq4845 provides direct connections for a 32.768KHz quartz crystal and a 3V backup battery. Through the use of the conditional chip enable output CE\OUT and battery voltage output VOUT pins, the bq4845 can write-protect and make nonvolatile external SRAMs. The backup cell powers the real-time clock and maintains SRAM information in the absence of system voltage.

The bq4845 contains a temperature-compensated reference and comparator circuit that monitors the status of its voltage supply. When the bq4845 detects an out-of-tolerance condition, it generates an interrupt warning and subsequently a microprocessor reset. The reset stays active for 200ms after VCC rises within tolerance, to allow for power supply and processor stabilization.

The bq4845 also has a built-in watchdog timer to monitor processor operation. If the microprocessor does not toggle the watchdog input WDI within the programmed time-out period, the bq4845 asserts WDO\ and RST\\. WDI unconnected disables the watchdog timer.

The bq4845 can generate other interrupts based on a clock alarm condition or a periodic setting. The alarm interrupt can be set to occur from once per second to once per month. The alarm can be made active in the battery-backup mode to serve as a system wake-up call. For interrupts at a rate beyond once per second, the periodic interrupt can be programmed with periods of 30.5us to 500ms.

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Real-Time Clock counts seconds through years in BCD format

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On-chip battery-backup switchover circuit with nonvolatile control for external SRAM

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Less than 500nA of clock operation current in backup mode

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Microprocessor reset valid to VCC =VSS

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Independent watchdog timer with a programmable time-out period

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Power-fail interrupt warning

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Programmable clock alarm interrupt active in battery-backup mode

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Programmable periodic interrupt

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Battery-low warning