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Sensor measures temperature with pinpoint accuracy

Santa Clara, Calif. — National Semiconductor Corp.'s TruTherm thermal management technology facilitates pinpoint-accurate temperature measurements for chips with integrated thermal diodes.

“Measuring the internal temperature of submicron CPUs and FPGAs with traditional methods generates results that are inaccurate and unpredictable,” said Suneil Parulekar, senior vice president of the company's analog products group.

When applying National's prior generation sensor (LM95221) in the 90 nanometer (nm) or less range, as seen in the top half of the photo below, these diodes display a large variation in temperature readings (anywhere from 0 to 6°C.) In the bottom half of the photo, however, using its TruTherm sensor, the temperature reading distribution is very tight (less than half a degree difference). By the way, the LM95221 sensor is pin compatible with the new TruTherm device.

As computing systems and consumer electronics incorporate more submicron processors and field-programmable gate arrays (FPGAs) that tend to run hot, cooling fans are needed. Pinpoint-accurate temperature readings enable higher levels of performance, extended system life and reduced acoustic noise, Parulekar said.

While the new technology won't eliminate fan usage, it will allow engineers to control the amount of time a fan is running, so it won't be operating 24 hours a day to cool a CPU, said Andrew Jue, marketing director for National's data conversion systems group.


In support of TruTherm, Intel will include additional parameters in the data sheets for its new 90-nm Pentium 4 processors, said Benson Inkley, senior processor applications engineer of Intel Corp. (Santa Clara, Calif.)

National is kicking off its TruTherm sensor family with the LF95231, a high-precision, dual remote-diode temperature sensor with ±0.75°C accuracy. It features a precision sigma-delta analog-to-digital converter (A/D converter) for reduced sensitivity to noise and includes digital filtering, remote-diode fault detection and local temperature sensing. The LM95231 is compatible with the System Management Bus (Sbus) 2.0 and I²C bus specifications.

Limited samples of the LM95231 temperature sensor, packaged in an 8-pin MSOP, are available now. Production quantities will be available in May 2005 and are priced at $1.50 in 1,000-unit quantities.Click here for the LM95231 data sheet.

National Semiconductor , 1-408-721-5000, www.national.com.

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