The modular Approach to Tire Pressure Monitoring Systems

Tire pressure monitoring is a proven safety enhancement to any vehicle, whether passenger car, light truck, heavy truck or bus. The challenges of meeting regional regulations, and OEM system compatibility, favor modular solutions for most vehicles.

A modular approach pairs the MLX91801, System in a Package (SIP) analog pressure sensor and sensor interface micro-controller, with an optimized RF Transmitter, the MLX72013. Adding an external roll sensor and peripheral passive support components yields a complete, cost effective, TPMS solution.

The MLX91801 contains blocks for control of the sensor interface, communication interface and power management blocks supporting extremely low power consumption in standby mode. The device measures pressure, temperature and supply voltage. The pressure sensing element is a MEMS based absolute resistive bridge pressure sensor. The communication interface provides commands for receiving and sending data to the host system. A standard software library with low-level routines gives access to all the IC’s functions. Application examples provided by Melexis offer an introduction to the Melexis microcontroller programming and allow quick custom developments.

The MLX91801 pressure sensor block offers 1% Full Scale accuracy. The default pressure range is 100 – 800 kPa. Other ranges are available by request.
The MLX72013 ASK / FSK transmitter IC is designed for applications in the license-free 433 MHz ISM (Industrial-Scientific-Medical) band air interface for wireless communications. 433 MHz is available for use worldwide. It has been designed to meet the latest evolution of the EN 300 220 telecommunications standard; but it can also be used in other countries with similar standards, e.g. FCC part 15.231.

The MLX71122 is a multi-channel receiver IC based on a double-conversion super-heterodyne architecture. It is designed to receive FSK and ASK modulated RF signals either in 8 predefined frequency channels or frequency programmable via a 3-wire serial programming interface (SPI). Thanks to its highly linear RSSI (Received Signal Strength Indication), the MLX71122 allows for automatic wheel identification hence providing users with further integration capabilities.

Ivan Zagan, Product Line Manager for TPMS at Melexis says:” Although the current trend for automotive TPMS sensors is in the direction of fully integrated solutions there is significant advantage in flexibility and cost for a modular solution”

Figure 1 shows an application example of the modular solution available with MLX91801 and a Melexis RF Transmitter IC, MLX72013.

Figure 2 shows a block diagram of the Melexis TPMS solution demo kit that is available. This demo board uses the MLX91801 TPMS sensor, the MLX72013 RF Transmitter IC and the MLX71122 RF Receiver IC. The kit comes with an LF/RF transceiver and antenna, with USB connection to a computer and read out software.