Dallas Semiconductor 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 ý1 minute per year (ý2 parts per million) in operation from 0 to 40ýC, 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 ý1 minute per month at 25ýC and ý40 minutes per year at 60ýC. The steady 32.768 kHz output of the DS32KHz can maintain the accuracy of real-time clocks within ý4 minutes per year (ý7.5 ppm) over the industrial temperature range (-40 to 85ýC) and within ý1 minute per year from 0 to 40ýC.

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 25ýC. 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.

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.

Isn't that a wonderful piece of trivia; that watch oscillators are trimmed for body temperature operation?

The need for more accurate real time clocks (RTCs) has been growing apace and some large data warehouse users have gone to the lengths of installing temperature compensation environments for their oscillators. With mammoth amounts of data being pushed around it is not uncommon for records to be almost simultaneously changed; if a receipt in inventory is recorded at a retailer's warehouse, for example, a demand for that inventory from a branch back order might pull it out immediately. If the RTC for the receipt and for the demand are not synchronized all sorts of strange negative numbers can come and haunt the system. The same is true with financial and share transactions.

The accuracy of this part is amazing and it will be a surefire best seller for the company; I will be interested in due course in learning how the compensation circuits operate, but obviously Dallas have learned a lot from monitoring battery temperatures.Continuous timekeeping is provided by a single battery back-up with the battery switch circuits internal to the part. In battery back-up mode current consumption is typically 1ýA. The part is being supplied in a standard pick-and-place BGA package with 36 pins, only four of them active connectors, that is 0.40 in. W x 0.45 in. L x 0.18 in. H. It is priced at $5.28 in 1000-piece lots.