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 (V_OUT) 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 V_CC 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.

• Real-Time Clock counts seconds through years in BCD format
• On-chip battery-backup switchover circuit with nonvolatile control for external SRAM
• 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

• Iq (Typ) (uA)
• 0.5
• Features
• External SRAM control, Integrated CPU supervisor, Parallel bus interface, 16 RTC bytes
• Rating
• Catalog
• Operating temperature range (C)
• 0 to 70
• Supply voltage (Max) (V)
• 5.5
• Supply voltage (Min) (V)
• 4.5

BQ4845的完整型号有：BQ4845S-A4TR，以下是这些产品的关键参数及官网采购报价：

BQ4845S-A4TR，工作温度：0 to 70，封装：SOIC (DW)-28，包装数量MPQ：1000个，MSL 等级/回流焊峰值温度：Level-1-260C-UNLIM，引脚镀层/焊球材料：NIPDAU，TI官网BQ4845S-A4TR的批量USD价格：5.775（1000+）

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