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M41T82：Serial I²C bus real-time clock (RTC) with battery switchover

The M41T8x are low-power serial I²C real-time clocks (RTCs) with a built-in 32.768 kHz oscillator (external crystal-controlled for the QFN16 and SO8 packages, embedded crystal for the SOX18 package). Eight bytes of the register map (see Table 2 on page 23) are used for the clock/calendar function and are configured in binary-coded decimal (BCD) format. An additional 17 bytes of the register map provide status/control of the two alarms, watchdog, 8-bit counter, and square wave functions. An additional seven bytes are made available as user SRAM.

Addresses and data are transferred serially via a two-line, bidirectional I²C interface. The built-in address register is incremented automatically after each WRITE or READ data byte. The M41T8x has a built-in power sense circuit which detects power failures and automatically switches to the battery supply when a power failure occurs. The energy needed to sustain the clock operations can be supplied by a small lithium button battery when a power failure occurs.

Functions available to the user include a non-volatile, time-of-day clock/calendar, two alarm interrupts, watchdog timer, programmable 8-bit counter, and square wave outputs. The eight clock address locations contain the century, year, month, date, day, hour, minute, second, and tenths/hundredths of a second in 24-hour BCD format. Corrections for 28, 29 (leap year), 30, and 31 day months are made automatically. The M41T83 is supplied in either a QFN16 or an SOX18, 300 mil SOIC which includes an embedded 32 KHz crystal. The SOX18 package requires only a user-supplied battery to provide non-volatile operation. The M41T82 is available only in an SO8 package.

Key Features

• Ultra-low battery supply current of 365 nA
• Factory-calibrated accuracy of ±5 ppm typical after 2 reflows (SOX18)
  • Much better accuracies achievable using built-in programmable analog and digital calibration circuits
• 2.0 V to 5.5 V clock operating voltage
• Counters for tenths/hundredths of seconds, seconds, minutes, hours, day, date, month, year, and century
• Automatic switchover and reset output circuitry (fixed reference)
  • M41T83S: VCC = 3.00 V to 5.50 V
  • M41T83R: VCC = 2.70 V to 5.50 V
  • M41T83Z: VCC = 2.38 V to 5.50 V
• Serial interface supports I2 C bus (400 kHz protocol)
• Programmable alarm with interrupt function (valid even during battery backup mode)
• Optional 2nd programmable alarm available
• Square wave output defaults to 32 KHz on power-up (M41T83 only)
• RESET (RST ) output
• Watchdog timer
• Programmable 8-bit counter/timer
• 7 bytes of battery-backed user SRAM
• Battery low flag
• Low operating current of 80 μA
• Oscillator stop detection
• Battery or SuperCap™ backup
• Operating temperature of –40 °C to 85 °C
• Package options
  • a 16-lead QFN (M41T83)
  • an 8-lead SOIC (M41T82) or
  • an 18-lead embedded crystal SOIC (M41T83)
• RoHS compliance: lead-free components are compliant with the RoHS directive

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Application Notes

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