The CMOS bq3285LF is a low-power microprocessor peripheral providing a time-of-day clock and 100-year calendar with alarm features and battery operation. The architecture is based on the bq3285 RTC with added features: century bit, low-voltage operation, 32.768kHz output, 126 additional bytes of CMOS, two shadow registers of last address used, and a day-of-month alarm to be compliant with the ACPI RTC specification.

A 32.768kHz output is available for sustaining power-management activities. The bq3285LF 32kHz output is always on whenever VCC is valid. In VCC standby mode, the 32kHz is active, and the bq3285LF typically draws 100uA. Wake-up capability is provided by an alarm interrupt, which is active in battery-backup mode. In battery-backup mode, current drain is less than 550nA.

The bq3285LF write-protects the clock, calendar, and storage registers during power failure. A backup battery then maintains data and operates the clock and calendar.

The bq3285LF is a fully compatible real-time clock for IBM AT-compatible computers and other applications. The only external components are a 32.768kHz crystal and a backup battery.

The bq3285LF is intended for use in 3V systems; however, it may also operate at 5V and then go into a 3V power-down state, write-protecting as if in a 3V system.

• ACPI-compliant day-of-month alarm
• Y2K century bit
• Direct clock/calendar replacement for IBM ® AT-compatible computers and other applications
• 2 index shadow registers
• 2.7\x965.5V operation
• 240 bytes of general nonvolatile storage
• Dedicated 32.768kHz output pin
• System wake-up capability\x97alarm interrupt output active in battery-backup mode
• Less than 0.55uA load under battery operation
• Selectable Intel or Motorola bus timing
• 24-pin plastic SSOP