Temperature Sensors Shrink While Accuracy Rises

As complex chips that run at faster speeds go into smaller and smaller systems, the chances that overheating can cause problems is growing. Component engineers are responding with temperature sensors that precisely monitor systems and shut them down before hardware fails or battery packs explode.

One problem with existing temperature sensors is that they aren't particularly accurate, so engineers have to guess when to shut down systems. This inaccuracy means shutting down the system at lower temperatures to compensate for the margin of error or taking chances by pushing the limits of the unit. "Some engineers don't want to shut the system down early, while others shut it down early since they don't know if a measurement of say 78 degrees actually means 80," says Mitch Polonsky, program manager at SMSC of Hauppauge, NY.

SMSC is unveiling a four-product line that lets engineers compensate for variations caused by circuit board traces, which can add as much as 4 degrees variation, and input from CPUs and graphic chips. This configuration function also lets engineers work with a variety of processors, providing more versatility than competing temperature sensors that are trimmed for use with a specific microprocessor.

SMSC's EMC1000 line also reduces overall size by using just two pins to measure two temperatures. That means a dual sensor can use just eight pins instead of 10. One version also includes a fan control and temperature sensor, eliminating the need for a second part. Pricing starts at 65 cents each in production quantities.

Taking another tack, AVX Corp. of Myrtle Beach, SC, is focusing on small size. Its NB23 Series (http://www.avx.com/docs/Catalogs/nb12-21.pdf) take little space, measuring only the 0.04 x 0.02 inches of an 0402 package. That's small enough to squeeze a temperature sensor into the battery pack. Along with handheld and portable electronics, the line aims at LCD displays, especially those used on high resolution color displays.

The parts have resistance values from 10Kohm to 100Kohm, with standard tolerances of 5, 10, and 20 percent. Maximum dissipation is 150 mW, with a thermal dissipation factor of 0.8 mW/degrees C. Pricing starts at 11 cents in quantities of 10,000.