Initiator device with integrated immobiliser “wakes up” powered-down systems

November 13, 2014 // By Graham Prophet
Combining features for wireless technology and automotive passive entry/start systems, Melexis' MLX74190 is a low-frequency (LF) initiator IC, consisting of two high power, independently programmable LF drivers plus built-in immobilisers.

The device is intended for wireless communication deployments where power efficient operation is of prime importance, in such diverse sectors as automotive, safety and building automation.

One of the main applications for this device is automobile remote passive start, where it is used to transmit a high power LF signal to wake-up the key inside the car. The key sends out its encrypted identification number to the car via a UHF signal, enabling the engine to start. It can also serve for a similar purpose with other vehicles, such as motorcycles, scooters, all-terrain vehicles (ATVs), jet skis, snowmobiles and motorboats, where the key holder can be detected when approaching the engine and will be able to activate it from a 'Start' button. Conversely it can serve as a 'dead man switch' so that if the driver falls off (from, for example, a jet ski) then the engine is automatically cut. It may be incorporated into building access systems, tyre pressure monitoring system (TPMS) initiators and pet identification systems.

Both of the LF drivers can be programmed to generate sine (1A peak maximum) or square (2.5A peak maximum) waves with frequencies between 109 kHz and 140 kHz and an output amplitude from 0.25V to 32V peak-to-peak. These drivers can be used in either full-bridge or half-bridge configurations and have sophisticated protection mechanisms which safeguard them against over-current and over-temperature conditions. Amplitude-shift keying (ASK) or phase-shift keying (PSK) modulation can be used to transmit LF telegrams to the key or LF receiver. A very flexible data programing method, allows supporting a large variety of encoding types.

The two built-in immobilisers support ASK and frequency-shift keying (FSK) modulation. These can be employed should the key's battery become depleted and therefore unable to generate a signal. Under such circumstances passive RFID communication can be initiated when the key comes into close proximity of the initiator device. The immobilisers are compatible with the most popular