M41T56
512 bit (64 bit x8) Serial Access TIMEKEEPER® SRAM

FEATURES SUMMARY
■ 5V ±10% SUPPLY VOLTAGE
■ COUNTERS FOR SECONDS, MINUTES, HOURS, DAY, DATE, MONTH, YEARS, AND CENTURY
■ YEAR 2000 COMPLIANT
■ SOFTWARE CLOCK CALIBRATION
■ AUTOMATIC POWER-FAIL DETECT AND SWITCH CIRCUITRY
■ I 2C BUS COMPATIBLE
■ 56 BYTES OF GENERAL PURPOSE RAM
■ ULTRA-LOW BATTERY SUPPLY CURRENT OF 450nA
■ LOW OPERATING CURRENT OF 300µA
■ OPERATING TEMPERATURE OF –40 to 85°C
■ AUTOMATIC LEAP YEAR COMPENSATION
■ SPECIAL SOFTWARE PROGRAMMABLE OUTPUT
■ PACKAGING OPTIONS INCLUDE:
– 28-lead SOIC and SNAPHAT® TOP (to be ordered separately)
– SO8

Figure 1. 8-pin SOIC Package


Figure 2. 28-pin SOIC Package


SUMMARY DESCRIPTION
The M41T56 TIMEKEEPER® is a low power, 512- bit static CMOS RAM organized as 64 words by 8 bits. A built-in 32,768Hz oscillator (external crystal controlled) and the first 8 bytes of the RAM are used for the clock/calendar function and are configured in binary coded decimal (BCD) format. Addresses and data are transferred serially via a twoline, bi-directional bus. The built-in address register is incremented automatically after each WRITE or READ data byte.
The M41T56 clock has a built-in power sense circuit which detects power failures and automatically switches to the battery supply during power failures. The energy needed to sustain the RAM and clock operations can be supplied from a small lithium coin cell.
Typical data retention time is in excess of 10 years with a 50mAh, 3V lithium cell. The M41T56 is supplied in an 8-lead Plastic SOIC package or a 28- lead SNAPHAT® package.
The 28-pin, 330mil SOIC provides sockets with gold plated contacts at both ends for direct connection to a separate SNAPHAT housing containing the battery and crystal. The unique design allows the SNAPHAT battery package to be mounted on top of the SOIC package after the completion of the surface mount process. Insertion of the SNAPHAT housing after reflow prevents potential battery and crystal damage due to the high temperatures required for device surfacemounting. The SNAPHAT housing is keyed to prevent reverse insertion. The SOIC and battery/crystal packages are shipped separately in plastic antistatic tubes or in Tape & Reel form.
Caution: Do not place the SNAPHAT battery/crystal package “M4Txx-BR12SH” in conductive foam as this will drain the lithium button-cell battery.

Figure 3. Logic Diagram


Absolute Maximum Ratings

Note: 1. For SO package, standard (SnPb) lead finish: Reflow at peak temperature of 225°C (total thermal budget not to exceed 180°C for between 90 to 150 seconds).
2. For SO package, Lead-free (Pb-free) lead finish: Reflow at peak temperature of 260°C (total thermal budget not to exceed 245°C for greater than 30 seconds).

CAUTION: Negative undershoots below –0.3V are not allowed on any pin while in the Battery Back-up mode.
CAUTION: Do NOT wave solder SOIC to avoid damaging SNAPHAT sockets.

Figure 4. 8-pin SOIC Connections Figure 5. 28-pin SOIC Connections


Figure 6. Block Diagram


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