The BQ4845 Real-time Clock is a low-power microprocessor peripheral that integrates a time clock, a 100-year calendar, and a 28-pin SOIC or DIP CPU manager. The BQ4845 is ideal for fax machines, photocopiers, industrial control systems, point of sale terminals, data loggers and computers.
Block Diagram
The BQ4845 provides direct connection between 32.768KHz quartz crystal and 3V backup battery. By using Conditional Chip Enable Output (CEOUT) and Battery Voltage Output (VOUT) pins, the BQ4845 can be write-protected and non-volatile external sram. The backup unit powers the real-time clock and maintains SRAM information when there is no system voltage.
The BQ4845 contains a temperature compensation reference and comparison circuit that monitors the state of its voltage supply. When the BQ4845 detects that the tolerance condition is exceeded, it generates an interrupt warning and the microprocessor resets. After the VCC is raised to within the tolerance, the reset remains active for 200ms to allow for power supply and processor stability.
Application Circuit
The BQ4845 also has a built-in watchdog timer to monitor the processor's performance. If the microprocessor does not switch the watchdog input (WDI) within the set timeout, BQ4845 asserts WDO and RST. The WDI does not connect. Disable the watchdog timer. Additional interrupts can also be generated based on clock alarm conditions or periodic Settings. The alarm interruption can be set to once per second or once per month. This alarm can be activated in battery backup mode as a wake-up call. For interrupts with rates greater than one per second, periodic interrupts can be programmed to range from 30.5µs to 500ms.
