M41T94MQ6F IC Chips Serial real-time clock with 44 bytes NVRAM and reset

M41T94

Serial real-time clock with 44 bytes NVRAM and reset

Features

■ Counters for tenths/hundredths of seconds, seconds,

   minutes, hours, day, date, month, year, and century

■ 32KHz crystal oscillator integrating load capacitance (12.5pF)

   providing exceptional oscillator stability and high crystal series

   resistance operation

■ Serial peripheral interface (2MHz SPI)

■ Ultra-low battery supply current of 500nA (max)

■ 2.7 to 5.5V operating voltage

■ 2.5 to 5.5V oscillator operating voltage

■ Battery low flag

■ Automatic switchover and deselect circuitry

■ 44 bytes of general purpose RAM

■ Programmable alarm and interrupt function

   (valid even during battery back-up mode)

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

■ Microprocessor power-on reset

■ Choice of power-fail deselect voltages (V_CC = 2.7 to 5.5V):

  – THS = V_SS; 2.55V ≤ V_PFD ≤ 2.70V

  – THS = V_CC; 4.20V ≤ V_PFD ≤ 4.50V

■ Packaging includes a 28-lead SOIC and SNAPHAT® top

   (to be ordered separately) or 16-lead SOIC

■ 28-lead SOIC package provides direct connection for

   a SNAPHAT top which contains the battery and crystal

■ RoHS compliant

  – Lead-free second level interconnect

Description

The M41T94 is a serial real-time clock with 44 bytes of NVRAM and a RESET output. A built-in 32,768Hz oscillator (external crystal controlled) and 8 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 RAM provide status/control of Alarm, Watchdog and Square Wave functions. Addresses and data are transferred serially via a serial SPI interface. The built-in address register is incremented automatically after each WRITE or READ data byte. The M41T94 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 SRAM and clock operations can be supplied by a small lithium button-cell 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. Other features include a Power-On reset as well as two additional debounced inputs (RSTIN1 and RSTIN2) which can also generate an output reset (RST). 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 ninth clock address location controls user access to the clock information and also stores the clock software calibration setting.

The M41T94 is supplied in either a 16-lead plastic SOIC (requiring user supplied crystal and battery) or a 28-lead SOIC SNAPHAT® package (which integrates both crystal and battery in a single SNAPHAT top). 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/crystal 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 surface-mounting. The SNAPHAT housing is also keyed to prevent reverse insertion.

The SOIC and battery/crystal packages are shipped separately in plastic anti-static tubes or in Tape & Reel form. For the 28-lead SOIC, the battery/crystal package (e.g., SNAPHAT) part number is “M4TXX-BR12SH”

Caution: Do not place the SNAPHAT battery/crystal top in conductive foam, as this will drain the lithium button-cell battery.

Absolute maximum ratings

1. 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.

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