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.
● Real-Time Clock counts seconds through years in BCD format
● Integrated battery and crystal
● On-chip battery-backup switch-over circuit with nonvolatile control for an external SRAM
● 130mAh battery capacity
● ±1 minute per month clock accuracy
● Less than 500nA of clock operation current in backup mode
● Microprocessor reset valid to VCC=VSS
● Independent watchdog timer with a programmable time-out period
● Power-fail interrupt warning
● Programmable clock alarm interrupt active in battery-backup mode
● Programmable periodic interrupt
● Battery-low warning
