RTC IC with 242x8 NVSRAM Alarm Wake-up


Product details


Iq (Typ) (uA) 0.5 Features RAM clear function, Multiplexed bus interface, 14 RTC bytes, 0.242-kB memory density Rating Catalog Operating temperature range (C) 0 to 70 Supply voltage (Max) (V) 7 Supply voltage (Min) (V) -0.3 open-in-new Find other Real-time clocks (RTCs) & timers

Package | Pins | Size

SOIC (DW) 24 160 mm² 15.5 x 10.3 open-in-new Find other Real-time clocks (RTCs) & timers


  • Direct clock/calendar replacement for IBM® AT-compatible computers and other applications
  • Functionally compatible with the DS1285
    • Closely matches MC146818A pin configuration
  • 2.7–3.6V operation (bq3285L);
    4.5–5.5V operation (bq3285E)
  • 242 bytes of general nonvolatile storage
  • 32.768kHz output for power management
  • System wake-up capability—alarm interrupt output active in battery-backup mode
  • Less than 0.5µA load under battery operation
  • Selectable Intel or Motorola bus timing
  • 14 bytes for clock/calendar and control
  • BCD or binary format for clock and calendar data
  • Calendar in day of the week, day of the month, months, and years, with automatic leap-year adjustment
  • Time of day in seconds, minutes, and hours
    • 12- or 24-hour format
    • Optional daylight saving adjustment
  • Programmable square wave output
  • Three individually maskable interrupt event flags:
    • Periodic rates from 122us to 500ms
    • Time-of-day alarm once per second to once per day
    • End-of-clock update cycle
  • 24-pin plastic DIP, SOIC, or SSOP
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The CMOS bq3285E/L is a low-power microprocessor peripheral providing a time-of-day clock and 100-year calendar with alarm features and battery operation. The bq3285L supports 3V systems. Other bq3285E/L features include three maskable interrupt sources, square-wave output, and 242 bytes of general nonvolatile storage.

A 32.768kHz output is available for sustaining power-management activities. Wake-up capability is provided by an alarm interrupt, which is active in battery-backup mode.

The bq3285E/L write-protects the clock, calendar, and storage registers during power failure. A backup battery then maintains data and operates the clock and calendar.

The bq3285E/L 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.

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Technical documentation

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Type Title Date
* Data sheet bq3285E/L - Real-Time Clock (RTC) datasheet (Rev. A) May 26, 2004
Application note U-502 Time-Base Oscillator for RTC IC Sep. 05, 1999

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