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Two-Fold High Power LF Initiator with Immobilizer


The Melexis MLX74190 is a low-frequency (LF) initiator composed of two high power LF drivers and built-in immobilizers.

The main application for the MLX74190 is automotive passive start, where the integrated circuit (IC) transmits a high power LF telegram to wake-up the key inside the car. The key then returns the authorization identification to the car through ultra high frequency (UHF) to enable the engine start.

The MLX74190 also features two built-in immobilizers (for both ASK and FSK communications), used when the battery of the key is depleted. In this case, the key is placed in a specific zone close to the initiator and a full passive Radio-Frequency IDentification (RFID) communication is initiated. The load modulation signal returns by the key is received and demodulated by the MLX74190.

The MLX74190 is also suitable for tire pressure monitoring system (TPMS) initiator or non-automotive applications such as: Dead man switch for 2-wheeler and off-road vehicles like all-terrain vehicles (ATVs), jet skis, snowmobiles ..., LF door opener or active RFID initiator.

The MLX74190 can also serve for a similar purpose with other vehicles such as motorcycles, scooters, ATV, 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 or as a dead man switch, so that if the driver falls off then the engine is automatically cut. In addition it may be incorporated into building access systems, TPMS initiators and pet identification system.

Both LF drivers are independently programmable to generate sine (max. 1Ap) or square (max. 2.5Ap) waves with a frequency from 109 kHz to 140 kHz and an output amplitude from 0.25 to 32Vpp. The two drivers can be used in full or half bridge configuration and are protected against overload (overcurrent and overtemperature). A built-in diagnosis function allows detecting any wrong connection with the LF antenna (short to GND, short to Vbat, open load or wrong resonance frequency).

The MLX74190 is supplied by an external VS voltage from 6-40 V and VDD voltage of typically 5 V. The VS voltage can be generated by an external DC-DC converter or by DC voltage from vehicle supply.

The MLX74190 is controlled through a standard SPI interface (SDI, SDO, SCK and NCS) and an interrupt pin is generated on-purpose by the IC. The MLX74190 is clocked either with a 2 MHz clock frequency signal coming from the MCU or by an on-chip oscillator connected to an external 4 MHz crystal or ceramic resonator.
Two-Fold High Power LF Initiator with Immobilizer - MLX74190

Features and benefits

  • High power drivers (2.5Ap in square mode)

  • Output power programmable from 0.25 to 32Vpp

  • Output frequency programmable from 109 kHz to 140 kHz

  • Full or half bridge capabilities

  • Antenna fault detection

  • Protected power outputs (overcurrent and T°)

  • Built-in ASK/FSK immobilizers

  • SPI port for easy control

Practical application

Car Immobilizer

Advanced and high performance security system-on-a-chip solution that prevents the car engine from running unless the correct key is present.

Read more
Used in these


  • Automotive - Body, HVAC, Comfort & Lighting
  • Building, Security, Home & Office Automation
  • White Goods & Household Appliances

Inspired Engineering

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