Eco-friendly Surface Mounting Real-time Clock

SGS-THOMSON Microelectronics has announced a new real-time clock (RTC) device that combines full compatibility with an industry standard function with a unique package option that both reduces costs and provides environmental benefits. The M48T86 contains a long life lithium battery, a quartz crystal and low power CMOS circuitry that provides a 128x8 static CMOS RAM, a power-fail control circuit and a real-time clock/100- year calendar circuit with programmable alarms.

The integral power-fail circuit constantly monitors the Vcc line, switching automatically to the lithium energy source whenever an out-of-tolerance condition occurs. At the same time, the chip is switched to its write-protected mode to prevent spurious write cycles. With a predicted worst-case battery life of more than ten years (at 25°C), this technique, in which SGS-THOMSON is an industry leader, allows long-term non-volatile data retention to be combined with the fast read/write times and unlimited write cycles of conventional SRAM.

The M48T86 is primarily designed for use in PC motherboards, where it provides the time and date functions, interrupt generation and a scratch pad memory for storing configuration parameters. Replacing up to 20 discrete components, the M48T86 is pin-compatible with the Dallas Semiconductor DS12887A and Benchmarq BQ3287A RTC devices but is distinguished from the competition by the unique SNAPHATÖ package option.

Developed by SGS-THOMSON, the SNAPHAT package comprises a JEDEC standard 330 mil SOIC containing the silicon circuitry and a removable pack (with gold plated contact pins) containing the battery and quartz crystal. The SOIC is soldered using conventional reflow techniques and when all board components are attached, the battery package is snapped to the sockets on the SOIC.

The SNAPHAT package brings a number of important benefits. First, it allows system manufacturers to employ self-contained battery backed devices on boards intended for Surface Mounting assembly, where the high soldering temperature would otherwise adversely affect the lithium batteries. SNAPHAT eliminates this problem because the battery is housed in a removable package that is simply snapped into the sockets on the SOIC after the reflow soldering stage. In addition, SNAPHAT allows spent batteries to be disposed of in an environmentally sound manner, while the easy battery replacement is useful in systems that must operate over periods of time greater than ten years or in high ambient temperatures.

SNAPHAT is a trademark of SGS-THOMSON.

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