On September 1, the National Highway Traffic Safety Administration (NHTSA) made it official: All new passenger cars sold in the U.S. must now have tire pressure monitoring systems (TPMS). Although NHTSA remained “technology neutral” in its mandate, the agency prescribed a set of requirements that lead automotive suppliers in a common direction. Monitoring systems must allow deflation of no more than 25 percent and must detect that deflation within 20 minutes. As such, makers of the systems are employing a so-called “direct” method of monitoring inflation pressures.
“We’ve stabilized on the direct method, where there are sensors inside the tire and they radio back to a central receiver on the vehicle,” says John McGowan, directors of Sense and Controls for Infineon Technologies North America. “The way the law was written, it left the direct method as the only available solution.”
To meet the demand for tens of millions of the system each year, semiconductor makers are rolling out new processors and sensors targeted directly at TPMS. On this page, we’ve collected information on devices from three companies – Freescale, Infineon, and Texas Instruments – that are taking aim at the growing TPMS market.
Infineon’s Integrated Solution
The Infineon SP35 Tire Pressure Sensor incorporates all the major active functions of wheel-mounted TPMS in a single package. The integrated device, mounted on a printed circuit board with a battery and antenna, enables tier-one suppliers to meet the requirements of the new regulations. Its single package integrates an MEMS pressure sensor, acceleration sensor and temperature sensor with an 8-bit controller and wireless communication module. It eliminates the need for separate communication chips, thus reducing complexity and reportedly cutting costs by about 10 percent.
Freescale’s Single-Package Solution
Freescale Semiconductor’s MPXY8300 solution incorporates a capacitive pressure sensor, an 8-bit microcontroller, two-axis accelerometer and radio frequency transmitter in one package. The unit’s capacitive pressure sensor is one of several low-power techniques that boost battery life beyond NHTSA’s ten-year requirement. The 8-bit MCU incorporates 512b of RAM and the RF transmitter includes an integrated charge pump at 315/434 MHz.
TI’s Acoustic Wave Sensor
Texas Instruments and Transense Technologies plc are using TI’s TMS320F28x digital signal controllers in the first targeted piezo-electric surface acoustic wave (SAW) system for TPMS. Unlike MEMS-based systems, which incorporate a battery, the passive SAW sensor incorporates a three-element die within a small gas-tight capsule. Pressure is transmitted via a diaphragm to deform the die and mechanically strain one of its elements. The sensor is interrogated by an RF signal and signals are transmitted via three resonant SAW frequencies, from which pressure and temperature are subsequently determined. Hence, the system requires no battery.