SUMMARY DESCRIPTION
The M48T08/18/08Y TIMEKEEPER® RAM is an 8K x 8 non-volatile static RAM and real time clock which is pin and functional compatible with the DS1643. The monolithic chip is available in two special packages to provide a highly integrated battery backed-up memory and real time clock solution.
The M48T08/18/08Y is a non-volatile pin and function equivalent to any JEDEC standard 8K x 8 SRAM. It also easily fits into many ROM, EPROM, and EEPROM sockets, providing the non-volatility of PROMs without any requirement for special WRITE timing or limitations on the number of WRITEs that can be performed.
The 28-pin, 600mil DIP CAPHAT™ houses the M48T08/18/08Y silicon with a quartz crystal and a long-life lithium button cell in a single 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 surface mounting. The SNAPHAT housing is 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 “M4T28-BR12SH” or “M4T32-BR12SH” (see Table 17., page 25).

FEATURES SUMMARY
■ INTEGRATED ULTRA LOW POWER SRAM, REAL TIME CLOCK, POWER-FAIL CONTROL CIRCUIT, AND BATTERY
■ BYTEWIDE™ RAM-LIKE CLOCK ACCESS
■ BCD CODED YEAR, MONTH, DAY, DATE, HOURS, MINUTES, and SECONDS
■ TYPICAL CLOCK ACCURACY OF ±1 MINUTE A MONTH, AT 25°C
■ AUTOMATIC POWER-FAIL CHIP DESELECT AND WRITE PROTECTION
■ WRITE PROTECT VOLTAGES
   (VPFD = Power-fail Deselect Voltage):
   – M48T08: VCC = 4.75 to 5.5V
      4.5V ≤ VPFD ≤ 4.75V
   – M48T18/T08Y: VCC = 4.5 to 5.5V
      4.2V ≤ VPFD ≤ 4.5V
■ SOFTWARE CONTROLLED CLOCK CALIBRATION FOR HIGH ACCURACY APPLICATIONS
■ SELF-CONTAINED BATTERY AND CRYSTAL IN THE CAPHAT™ DIP PACKAGE
■ PACKAGING INCLUDES A 28-LEAD SOIC AND SNAPHAT® TOP (to be ordered separately)
■ SOIC PACKAGE PROVIDES DIRECT CONNECTION FOR A SNAPHAT TOP WHICH CONTAINS THE BATTERY AND CRYSTAL
■ PIN AND FUNCTION COMPATIBLE WITH DS1643 and JEDEC STANDARD 8K x8 SRAMs
■ RoHS COMPLIANCE
   Lead-free components are compliant with the RoHS Directive.