BQ4847

具有 NVSRAM 控制、看门狗定时器、上电复位、中断电池低电警告的 RTC

The bq4847 Real-Time Clock Module is a low-power microprocessor peripheral that integrates a time-of-day clock, a 100-year calendar, a CPU supervisor, a battery, and a crystal in a 28-pin DIP module. The part is ideal for fax machines, copiers, industrial control systems, point-of-sale terminals, data loggers, and computers.

The bq4847 contains an internal battery and crystal. Through the use of the conditional chip enable output CE\OUT and battery voltage output VOUT pins, the bq4847 can write-protect and make nonvolatile an external SRAM. The backup cell powers the real-time clock and maintains SRAM information in the absence of system voltage.

The bq4847 contains a temperature-compensated reference and comparator circuit that monitors the status of its voltage supply. When an out-of-tolerance condition is detected, the bq4847 generates an interrupt warning and a microprocessor reset. The reset stays active for 200 ms after VCC rises within tolerance to allow for power supply and processor stabilization.

The bq4847 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, the bq4847 asserts WDO\ and RST\\. WDI unconnected disables the watchdog timer.

The bq4847 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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Integrated battery and crystal

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On-chip battery-backup switch-over circuit with nonvolatile control for an external SRAM

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130mAh battery capacity

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±1 minute per month clock accuracy

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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