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Date: 14th July 2011

IC automatically operates auto- windshield glass wipers sensing mist, fog, rain

Automatic windshield wiper IC from Melexis responses automatically when mist, fog, rain or road spray begin to obstruct light transmission through the front windshield glass in cars and other automotives. The new MLX75308 rain sensor semiconductor chip is a single device solution.

The MLX75308 controls all the major components found in a rain and light sensor module typically applied behind the front windshield of an automobile. The sensor system consists of Near Infrared LEDs, Photodiodes, an MLX75308, a microcontroller and, in many instances, a Network Bus interface IC. The significant challenge addressed by the MLX75308 is the ability to provide sensitive detection of raindrops or mist in the presence of a highly dynamic light load from the sun. Melexis says previous solutions to this challenge involved expensive optical waveguides or elaborate algorithm which reduced responsivity and increased occurrence of false wipes. The MLX75308 separates and suppresses the sun signal from the rain signal being measured by the photodiodes.

Automotive OEMs often prefer to optimize automatic wiper systems to appeal to their typical consumer's preferences and their vehicles market segment positioning. Some manufacturers prefer a more relaxed rate of wiping, prioritizing that over a perfectly clear windshield. Others will activate the wipers at the slightest suggestion of rain. Running the headlights whenever the wipers activate is desired by some OEMs while others will consider the ambient light level input to determine when or if to automatically switch on the headlamps. By presenting the signal data to the ECU on-demand and in a digital form via SPI the MLX75308 enables the system integrator or OEM to determine how the sensor data will affect system level behavior.

MLX75308 is designed to be flexible enough to cope with a wide variety of windshield angles (from 40° to 90°) as well as different tinting and shading. Sensor implementations may demand a larger area of sensing coverage, more LED's and photodiodes to improve rain detection thresholds or less and fewer to optimize cost and size. Systems also need to work over a wide current range from picoamps to milliamps as the difference between light levels on a bright, sunny day are vastly different than when driving at night. Melexis says the MLX75308 can address all these options with its programmable analog signal control chain and 16 bit ADC and digital signal processing on chip. This combination allows the device to address a very high dynamic range on both input and output, claims Melexis.

The MLX75308 is configured in a 4x4 QFN package. According to Melexis the automatic wiper control data can as well serve for headlight control, sunlight load sensing in HVAC controls, mist and condensation controls for automatic climate controls. The flexibility of the MLX75308 can allow for creative applications circuits to bring about highly versatile sensor modules. Melexis.

Another advantage of this chip is rain light module can easily become a sensor cluster feeding many types of information to several different systems. Far Infrared non-contact temperature sensors could be included to provide inside and outside temperature measurement.

Samples of the Melexis MLX75308 are currently available.

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