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  • Tire Pressure Monitoring Sensor

  • Created: Sep 16, 2015

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In vehicles, tires need proper inflation so that it will be comfortable, safe and fuel efficient in driving. Many drivers took for granted the proper inflation of tires, risk driving with improperly inflated tires. An example of this is a car that has a proper inflation pressure in a high altitude location will be under-inflated when it is driving in a lower altitude. Similarly, a tire with a proper inflation pressure in lower altitude will be over-inflated when driving in higher altitude. The use of the Tire Pressure Monitoring Systems (TPMS) helps drivers with precise tire pressure measurement by providing individual tire readings. The Freescale’s FXTH870s family of tire pressure monitoring sensors provides the lowest transmitting power consumption, largest customer memory size and unique dual-axis accelerometer architecture.

The TPMS can operate at 315 or 434MHz ISM band RF transmitter, the circuit is design for a 315MHz ISM band. The RF embedded module in the FXTH8709226T1 consists of an RF output driver for an antenna and a hardware data buffer for automated output or direct control from the MCU. The TPMS has a pressure sensor, accelerometer, and temperature sensor in its sensor measurement interface. It has an external 26MHz Oscillator connected to XI and XO to be used by the internal PLL for creating carrier frequencies and data rates for the RF pin. A surface mount battery contacts is provided for its supply. The digital circuit is supplied through VDD and VSS pins, VSS for the positive supply and Vss for the ground. The analog circuit is supplied through VDDA and VSSA, VDDA for the positive supply and VSSA for the ground.

The FXTH8709226T1 has a pressure range starting from 100k to 900kPa that is applicable for high pressure TPMS supporting cars and light trucks in monitoring tire pressure. It is usually situated in all four tires including the spare. See other freescale TPMS for different pressure range and vehicle classification.