M41T81SM6F Serial I²C RTC with Battery Switchover 200ns Time-Keeping Low 400nA Current 2.5-5.5V Operation Industrial -40°C to +85°C 8-DIP Package Integrated Oscillator & Square Wave Output

M41T81SM6F Serial I²C RTC with Battery Switchover 200ns Time-Keeping Low 400nA Current 2.5-5.5V Operation Industrial -40°C to +85°C 8-DIP Package Integrated Oscillator & Square Wave Output

Features

■ Counters for tenths/hundredths of seconds, seconds, minutes, hours, day, date, month, year, and century

■ 32 KHz crystal oscillator with integrated load capacitance (12.5 pf) which provides exceptional oscillator stability and high crystal series resistance operation)

■ Oscillator stop detection (monitors clock operation)

■ Serial interface supports I2C bus (400 kHz protocol)

■ Ultra-low battery supply current of 0.6 µA (typ)

■ 2.0 to 5.5 V clock operating voltage

■ Automatic switchover and deselect circuitry (fixed reference) which provides full operation in 3.0 V applications)

■ VCC = 2.7 to 5.5 V

■ 2.5 V ≤ VPFD ≤ 2.7 V

■ Power-down time-stamp (HT bit) which allows determination of time elapsed in battery backup

■ Battery low flag

■ Programmable alarm and interrupt function (valid even during battery backup mode)

■ Accurate programmable watchdog timer (from 62.5 ms to 128 s)

■ Software clock calibration (to compensate for crystal deviation due to temperature)

■ Operating temperature of –40 to 85 °C

■ Package options include an 8-lead SOIC or 18-lead embedded crystal SOIC

Applications

1. Industrial Automation & Control Systems

* Use Cases: Programmable Logic Controllers (PLCs), Industrial PCs (IPCs), Distributed Control Systems (DCS), sensor data loggers.
* Why: Its extended temperature range (-40°C to +85°C) and through-hole 8-DIP package make it robust enough for harsh industrial environments, ensuring accurate event time-stamping and logging.

2. Telecommunications & Network Infrastructure
* Use Cases: Routers, switches, base station controllers, Network-Attached Storage (NAS).
* Why: This equipment needs precise timekeeping for synchronizing logs, managing network traffic, and error tracking. Its I²C interface allows easy connection to the main processor, and the battery switchover functionality guarantees time is maintained during main power loss.

3. Consumer Electronics & Smart Appliances
* Use Cases: Advanced smart meters, solar inverters, high-end appliances (e.g., ovens, washing machines), Point-of-Sale (POS) terminals.
* Why: The ultra-low power consumption (400nA) is critical for battery-backed devices. For example, in a smart meter, the backup battery can maintain timekeeping during a main power failure thanks to the RTC's minimal draw, ensuring critical event timing is recorded.

4. Data Logging & Measurement Equipment
* Use Cases: Environmental monitoring stations, vehicle data recorders, scientific instrumentation.
* Why: Providing an accurate timestamp for every data point is essential. The battery switchover feature ensures time is never lost during power outages, and the integrated oscillator simplifies design.

Description

The M41T81S is a low-power serial real-time clock (RTC) with a built-in 32.768 kHz oscillator (external crystal controlled). Eight bytes of the SRAM are used for the clock/calendar function and are configured in binary-coded decimal (BCD) format. An additional 12 bytes of SRAM provide status/control of alarm, watchdog and square wave functions. 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 M41T81S 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 supply when a power failure occurs. Functions available to the user include a non-volatile, time-of day clock/calendar, alarm interrupts, watchdog timer and programmable square wave output. 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 - valid until year 2100), 30 and 31 day months are made automatically.

The M41T81S is supplied in either an 8-pin SOIC or an 18-pin 300 mil SOIC package which includes an embedded 32 KHz crystal.

The 18-pin, embedded crystal SOIC requires only a user-supplied battery to provide non volatile operation.

INFORMATION

Drawing

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