Pressure sensors help OEMs comply with vehicle emission limits
PCB-less pressure sensor ICs deliver what Melexis claims is the highest degree of accuracy over lifetime. The integrated pressure sensors are intended for use in automotive engine management.
The MLX90824 determines the absolute pressure, then delivers a digital output signal using the SENT protocol and the partner MLX90822 IC provides an analogue output voltage. These factory calibrated devices measures pressure spans from 1.0 to 4.0bar.
Accurate and stable pressure measurements allow optimal engine management to guarantee fuel savings and emission reductions. Laurent Otte, senior product line manager at Melexis said: “An accuracy of +/-0.5 per cent FS (full scale) is maintained over the course of the sensor’s working lifespan. This accuracy is not impacted by the sensor integration thanks to the PCB-less packaging”.
The MLX90824 and MLX90822 have a sensor readout circuit, digital hardware, voltage regulators and SENT or analogue output drivers, and all the essential passive components, said Melexis. A pre-calibrated NTC thermistor (negative temperature co-efficient) input is available for the MLX90824 (SENT output). This allows customers to interface the NTC through the pressure sensor without end-calibration. Over-voltage (+40V) and reverse voltage (-40V) protection mechanisms are also integrated. This protection range allows lorries and trucks to benefit from these pressure sensors, said Melexis. The pressure sensors have an operating temperature range that spans from -40 to +160 degrees C and can be exposed to 170 degree C temperatures for a short period of time. This characteristic supports downsized engine architectures, added Melexis.
The MEMS, sensing element of the MLX90824 and MLX90822, consists of a micro-machined diaphragm. It is bonded around a cavity that has been etched into a silicon substrate. This cavity contains a reference vacuum and the diaphragm reacts to any change in the ambient absolute pressure. Piezo-resistive elements implanted into the diaphragm are configured to create a Wheatstone bridge that generates a signal. The accompanying front end electronics subsequently amplify the signal and convert it into a digital format. The 16-bit digital signal processing (DSP) undertakes temperature compensation. The result is provided through a SENT or analogue output.
The MLX90824 and MLX90822 have been developed as a Safety Element out of Context (SEooC) in accordance with ISO 26262. It supports ASIL B system integration for the MLX90824 and ASIL A for the MLX90822.
In addition to fuel savings and emission reductions in vehicles, motorcycles or any equipment running on small engines, such as chainsaws or lawn mowers need to use a sensor with a very fast update rate and step response. The MLX90822 has an output step response three times faster than any other pressure sensor ever made by Melexis.
