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M41T93：Serial SPI bus real-time clock (RTC) with battery switchover

The M41T93 is a low-power serial SPI bus real-time clock (RTC) with a built-in 32.768 kHz oscillator (external crystal-controlled for the QFN16 package, and embedded crystal for the SOX18 package). Eight bytes of the register map 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 serial SPI bus-compatible interface. The built-in address register is incremented automatically after each WRITE or READ data byte. The M41T93 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, alarm interrupt, 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 M41T93 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.

Key Features

• Ultra-low battery supply current of 365 nA
• Factory calibrated accuracy ±5 ppm typical after 2 reflows (SOX18) (much better accuracies are 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): M41T93S: VCC = 3.0 V to 5.5 V; M41T93R: VCC = 2.7 V to 5.5 V; M41T93Z: VCC = 2.38 V to 5.50 V
• Compatible with SPI bus serial interface (supports SPI mode 0 [CPOL = 0, CPHA = 0])
• 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)
• 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 supercapacitor backup
• Operating temperature of –40 °C to +85 °C
• Package options include a 16-lead QFN and an 18-lead embedded crystal SOIC

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