BQ3285ES

The BQ3285ES is a low-power CMOS real-time clock (RTC) IC designed for direct clock/calendar replacement in IBM AT-compatible computers and other applications. It integrates 242 bytes of nonvolatile SRAM (NVSRAM) for general storage, along with 14 bytes dedicated to clock/calendar and control functions. The device supports both BCD and binary time formats, 12/24-hour modes, and includes automatic leap-year adjustment and optional daylight saving adjustment. Key features include an alarm interrupt output that remains active in battery-backup mode, a programmable square wave output (32.768 kHz), and three individually maskable interrupt event flags for periodic rates, time-of-day alarm, and end-of-clock update cycle. The RTC operates from a supply voltage of 2.5V to 4V (note: manufacturer page specifies 4.5-5.5V for BQ3285E variant) and draws a typical supply current of 300 µA at 5V. Under battery backup, the current consumption is less than 0.5 µA. The device is available in a 24-SOIC (0.295", 7.50mm Width) surface-mount package, with an operating temperature range of 0°C to 70°C. It is functionally compatible with the DS1285 and closely matches the MC146818A pin configuration. The BQ3285ES is suitable for timekeeping and alarm applications in computing, industrial, and consumer systems requiring battery-backed real-time clock functionality.