TEMPERATURE-COMPENSATED CRYSTAL OSCILLATOR (TCXO) FROM DALLAS SEMICONDUCTOR IS INDUSTRY'S MOST ACCURATE
DALLAS, TEXAS-October 12, 1998-Dallas Semiconductor today announced an oscillator that meets the precision timekeeping requirements of large computer networks, financial transaction processing applications, and timed-access communications. A temperature-compensated crystal oscillator (TCXO), the DS32KHz 32.768 KHz TCXO meets the 1998 European network server recommendation for real-time clock (RTC) accuracy.
 The new device provides accuracy as great as ±1 minute per year (±2 parts per million) in operation from 0 to 40°C, making it the industry's most accurate 32.768-kHz oscillator. Economical quartz crystals provide the time references in real-time clock circuits for computers and many other electronic systems. Unfortunately, the electromechanical sensitivities of these crystals can cause instabilities in their output frequencies. As a result, uncompensated crystals can cause system clocks to gain or lose as much as 100 minutes per year in operation over the industrial temperature range.
The accepted standard of accuracy in modern electronic systems is ±1 minute per month at 25°C and ±40 minutes per year at 60°C. The steady 32.768 kHz output of the DS32KHz can maintain the accuracy of real-time clocks within ±4 minutes per year (±7.5 ppm) over the industrial temperature range (-40 to 85°C) and within ±1 minute per year from 0 to 40°C.
Device Sets a New Standard of Accuracy
"Accurate timekeeping is very important in network servers that have lots of PCs connected to them," said Doug Cole, product manager. "With timed-access communications, there's a need for accuracy and synchronization." The same need exists for financial transactions processed at point-of-sale terminals. When a great deal of information is coming in and every system time-stamps it differently, more accurate references are needed.
"Nobody puts an RTC in a system and expects it to keep inaccurate time," Cole said. "People don't understand why a $9.95 watch can keep accurate time but a $3,000 PC and a $20,000 server can't. Watches keep good time because they're trimmed to operate at body temperature."
Real time clocks are calibrated to keep time accurately at 25°C. If temperatures are hotter or colder, the clocks run more slowly. Accuracy over temperature typically depends on crystal characteristics, and higher accuracy over temperature is achievable by trimming the crystal.
Accuracy needs to be repeatable day in and day out, Cole said. Timekeeping in remote applications that operate at elevated temperatures can be significantly inaccurate. The effect of temperature on accuracy is cumulative; it is not self-correcting.
Accurate, Economical Replacement
The DS32KHz is an accurate, economical replacement for standard 32.768-kHz crystals and oscillators. The TXCO's output can be used to drive the X1 input of most RTC chips, chipsets and other ICs that contain RTCs.
Inside the compact, surface mount package are a quartz crystal and a temperature-compensation IC. The compensation IC employs low current oscillator technology and Dallas' proprietary thermal-sensing technology. No external trimming capacitors are required, and no calibration is needed after the device leaves the factory. Patent protection for the compensation chip is pending.
Dallas supplies the device in an industry-standard Ball-Grid Array (BGA) package that is compatible with pick-and-place technology and conventional convection reflow assembly methods. The package measures 0.40 wide, 0.45 long, and 0.18 inches high; it has 36 pins, but only four pin connections are required for operation.
Recommended Land Pattern Layout
Dallas provides a land pattern layout for the package that is compatible with standard 32.768 kHz crystals or the DS32KHz. No hardware modifications are required. The recommended layout, available on the Dallas Semiconductor Web site, can be used in both new designs and board revisions.
A single backup battery powers the DS32KHz and the RTC, providing continuous timekeeping if system power fails. The TCXO integrates the required battery switch circuitry.
Available in commercial and industrial temperature versions, the DS32KHz operates from supplies ranging from 2.7 to 5.5 volts, and current consumption in battery-backed mode is 1µA typical. The device is currently available from stock. Dallas Semiconductor is the industry's largest supplier of standalone integrated circuit RTCs.
Dallas Semiconductor designs, manufactures and markets CMOS chips and chip-based subsystems. In its 14-year history, the company has sold its products to more than 15,000 customers worldwide. Major markets include Original Equipment Manufacturers (OEMs) in personal computers, telecommunications, office equipment, instrumentation, factory automation, medical equipment and mainframe computers.
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