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IC supplants quartz-based solutions

Posted: 28 Apr 2005 ?? ?Print Version ?Bookmark and Share

Keywords:real-time clock? rtc? dallas semiconductor? ds3231? temperature compensated crystal oscillator?

Designed to replace quartz crystals in applications in which timekeeping accuracy is critical, a new real-time clock (RTC) from Dallas Semiconductor has been integrated with several functions that enable it to offer better than 2 minutes per year accuracy over a wide operating-temperature range.

The DS3231 clock chip integrates a highly stable temperature compensated crystal oscillator (tcxo), RTC and a 32.768KHz crystal into a single, 16-pin, 300 mil SOIC package. It also includes a digital temperature sensor that is accessed through the I?C port and provides 3C accuracy.

The I?C-integrated RTC device is targeted at servers, electricity meters, security and access control systems, fleet management, telematic systems, GPS and navigation equipment, POS terminals, ATMs or any other type of application that requires timekeeping accuracy.

The chip replaces conventional clock accuracy devices such as crystals, which produce unstable output frequencies due to their electromechanical and thermal sensitivities. Manufacturers and system users typically rely on three options to compensate for the temperature drift: in-line calibration during the manufacturing process, microprocessor-scheduled updates using crystal correction codes based on ambient temperature, or in-field servicing to correct timekeeping.

Conventional methods for attaining RTC accuracy better than the traditional 100 minutes per year are both cumbersome and expensive. Compared with alternative crystal-based solutions, the DS3231 provides up to five times better accuracy over the entire operating-temperature range of -40C to 85C, according to the company.

"Each of these methods can be costly," said Paul Nunn, business manager of TCXO products at Dallas, a wholly owned subsidiary of Maxim Integrated Products. "The resulting accuracy is typically no better than 20ppm or 10 minutes per year over a narrower, 0 to -40C temperature range."

The DS3231 RTC is available in commercial and industrial temperature versions and operates from 2.3V to 5.5V power supplies. In 25,000-unit quantities, the device costs $2.14 each.

- Ismini Scouras


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