bq4287

The CMOS bq4287 is a low-power microprocessor peripheral providing a time-of-day clock and 100-year calendar with alarm features and battery operation. Other features include three maskable interrupt sources, square wave output, and114 bytes of general nonvolatile storage.


The bq4287 write-protects the clock, calendar, and storage registers during power failure. The integral backup energy source then maintains data and operates the clock andcalendar.


The bq4287 uses its integral battery-backup controller and battery to make a standard CMOS SRAM nonvolatile during power-fail conditions. During power-fail, the bq4287 automatically write-protects the external SRAM and provides a VCC output sourced from its internalbattery.


The bq4287 is a fully compatible real-time clock for IBM AT-compatible computersandotherapplications.


As shipped from Benchmarq, the backup cell of bq4287 is electrically isolated from the memory. Following the first application of V_CC, this isolation is broken, and the backup cell provides data retention to the clock, internal RAM, V_OUT, and CE_OUT on subse-quentpower-downs.


The bq4287 is functionally equiva-lent to the bq4285, except that the battery (16, 20) and crystal pins (2,3) are not accessible. These pins are connected internally to a coin cell and quartz crystal. The coin cell of bq4287 provides 130mAh of capacity. For a complete description of features, operating conditions, electrical characteristics, bus timing, and pin descriptions, see the bq4285 data sheet.