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Motorola unveils low-power tire sensor

Posted: 26 May 2003 ?? ?Print Version ?Bookmark and Share

Keywords:motorola? automotive tpm systems? tire sensor?

Motorola Corp. rolled out an automotive tire pressure sensor which it claims to consume about one-tenth as much power as competing sensors. The company is aiming the new sensor at automotive TPM systems, which are expected to reach about 100 million tires over the next decade.

Motorola said that the new sensor, housed in a super small outline package measuring 0.3 inches on a side, is a piece of an electronics puzzle that could enable TPM systems makers to achieve a 10-year battery life in their products.

"It's directly targeted at the tire pressure monitoring market," said Mark Shaw, manager of systems engineering for Motorola's sensor products. "If we had built this for any other market, we wouldn't have paid as much attention to power consumption."

The new pressure sensor is a surface micro-machined capacitive type, whereas most TPM sensors use bulk micro-machined piezo-resistive technology. Motorola engineers said that because it employs capacitive technology, it can be made smaller and less power-hungry. A low-power standby oscillator in the device keeps time and wakes up a measurement system's microcontroller system as needed, thus dramatically reducing the device's standby current requirements.

"Piezo-resistive elements typically use milliamps of current," Shaw said. "But capacitive pressure sensors use significantly less power, so the current [drain] is on the order of microamps."

Shaw said the company's internal tests revealed that the sensor, used along with a Motorola microcontroller, can meet a ten-year-life for a typical 250 mA-hour battery.

Motorola announced the new device as part of a four-part chipset. The other three devices, which were already on the market, include an integrated 8-bit microcontroller and RF transmitter, an RF receiver that can be used for TPM or remote keyless entry, and a 16-bit microcontroller.

The chipset is expected to be used in so-called "direct" TPM, in which a tire-mounted sensor and transmitter send RF signals to a dashboard-mounted receiver, which then works in conjunction with a microcontroller to determine whether one of the tires is under- or over-inflated.

TPMs are expected to grow rapidly in popularity in the next few years because a federal mandate calls for implementation of such systems on 10 percent of vehicles sold in the U.S. by November 2003.

Motorola plans to sell the chipset to tier-one automotive suppliers.

- Charles J. Murray

EE Times

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