Freescale rolls smallest TPMS module

October 20, 2014 // By Christoph Hammerschmidt
With the model FXTH87, Freescale has introduced the world's smallest Tire Pressure Measurement System (TPMS) sensor. The sensor offers very low weight and power consumption but lacks strong data encryption despite earlier hacking attacks to the RF connection between TPMS and vehicle.

The FXTH87 sensor weighs only 0.3 grams and is 50% smaller than competing products. Despite its small dimensions, it comprises a dual-axis accelerometer architecture, sensors for pressure and temperature and an integrated 8-bit MCU along with the related RF transmitter and low frequency receiver circuitry. Stored on the chip are some basic software libraries.

In the past, the communication path between TPMS and the related ECU in the vehicle has already proved unsafe - American hackers have staged a well-documented attack to this RF link. Nevertheless, The FXTH87 does not provide full-fledged data encryption. Instead, it just offers some data randomisation, explained Marc Osajda, Busines Development Manager MEMS Sensors for Freescale. "The customers do not require it", he added. Osajda said he is aware that at least one European OEM intends to fully encrypt the TPMS radio link, and Freescale will equip the next TPMS generation with a hardware encryption module on the chip.

Tire pressure monitoring systems are increasingly regarded as an element of traffic safety and fuel economy. In the United States, they are become mandatory in new cars already in 2005; in the European Union, their use will be compulsory starting November 2014. Similar rules are in effect in Asian countries. TPMS will represent more than 25 of the total pressure measurement market for automotive sensors by 2015.

The FXTH87 comes in a 7 x 7 x 2.2 mm package, the smallest footprint in this market environment. It also features the industry lowest RF power consumption of 7 mA ldd. The battery lifetime however cannot specified exactly since the true power consumption greatly depends on how the respective OEM has programmed the devices. In particular, frequent data transmissions greatly affect the battery lifetime. A realistic expectation would be sometimes between six and ten years, Osajda said.

While the current TPMS sensors are bonded into the wheel hub, future generations could be placed directly into the tire, Osajda