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Temp sensors tout speed, stability

Posted: 22 Sep 2005 ?? ?Print Version ?Bookmark and Share

Keywords:tsic? temperature sensor? zmd america?

The TSic temperature sensor family is said to be fully tested and calibratedwith absolute measurement accuracy on deliveryno further calibration needed.

The new family combines outstanding accuracy with long term stability, yet it is very simple to use, said Frank Cooper, president of ZMD America.

The sensors employ a high-precision bandgap reference with a proportional-to-absolute temperature (PTAT) output; a low-power, precision analog-to-digital converter (A/D converter); and an on-chip DSP core with E2PROM to precisely calibrate the output temperature signal.

A joint venture between ZMD America and IST AG (Wattwil, Switzerland) resulted in the development of this temperature sensor family with a rapid response time. Comparable products with accuracy of less than 0.5 would cost a lot more and possess a significantly higher maximum supply current, Cooper said.

The response time of the TSic family is extremely fast (63 percent of a temperature step is reached after 0.8s in an SOP-8 and/or e-line package, and can be made accurately in less than three seconds when measured in water), Cooper said. The chip on flex (COF) package is even faster, he said. "In customer-specific product versions, the TSic COF device can provide a new measurement every 4 ms. This is a key feature for improved accuracy and performance over other devices," Cooper said.

Alternatives to digital IC-based temperature sensors include passive sensors like negative temperature coefficient (NTC) thermistors and analog ICs, which lack precision, require additional components, and have an analog signal that is noise sensitive and requires a costly A/D converter, Cooper said.

Although platinum sensors like resistance temperature detectors (RTDs) are very precise, they also require additional components, require more power and have noise issues, he said.

This is ZMD's first standalone temperature sensor. Previously, they did make temp sensors for their ASIC products. ZMD provided the high precision bandgap reference with PTAT output, as well as the ZACwire interface, which offers many advantages for sensor interfacing, Cooper said. "ZACwire is very simple for device interfacing and only needs one input per attached sensor at the microcontroller level," he said.

Prior to the joint venture, IST AG produced platinum- and nickel-based temperature sensors. The TSic family represents IST AG's first IC-based temperature sensor. The company is banking on its 14 years experience calibrating millions of highly accurate platinum sensors, which it applied to the TSic family, Cooper said.

Previous-generation products from other vendors also offer temperature sensors in the -50C to 150C temperature range. In comparison with 20 similar products over the same temperature range, however, competing sensors have a resolution starting at 0.5C to &plsumn;3C, whereas the TSic product family provides accuracy of 0.1C, 0.3C or 0.5C, Cooper said.

Another key feature of these devices is low power consumption, which reduces self heating and is necessary for wireless or battery driven applications. If a temp sensor has high self heating such as 0.3C or more, which is very typical today, this will limit high accuracy measurement. "Self heating is different in different environmental conditions and therefore can not be compensated at the calibration level," Cooper said.

- Bettyann Liotta


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