Pressure sensor IC for hybrid vehicles

Implementing fuel pressure vapour detection using so-called EVAP (evaporation) systems is increasingly important for automotive manufacturers, as more regions introduce strict legislation which prohibits the venting of fuel vapour to the atmosphere. As vapour builds up inside fuel tanks and crank cases, the EVAP systems are designed to capture, store and responsibly dispose of the vapour, preventing it from escaping into the air. Pressure sensors that can operate at very low pressures, like the MLX90821, are a crucial part of these systems, as they are able to detect even the smallest leaks that can potentially appear at any point in the EVAP system.

“The MLX90821 is a relative pressure sensor that has the range, reliability, stability and accuracy to cover EVAP systems for both internal combustion and hybrid engines,” commented Laurent Otte, Pressure Sensors Product Line Manager, Melexis. “This gives Tier 1 and module manufacturers the ability to standardise on a single design for both types of engine, using a sensor IC that is factory calibrated but can also be customised for each individual application. Its robust, easy to seal packaging is certified to operate between -40℃ and +150℃ and comes with full PPAP support.”

Fuel vapour pressure measurement is even more complex in hybrid vehicles, creating demand for more capable sensing solutions. Also, as EVAP systems in both ICE (internal combustion engine) and hybrid vehicles may feature several pressure sensor ICs, design flexibility and simplicity are critical. While being small enough to be used in any size module, the level of integration provided through the system-in-package approach makes designing with the MLX90821 simple, providing what is essentially a ‘plug-n-play’ approach. While both analogue and SENT outputs are provided, the DSP offers the ability to make full use of the SENT interface’s fast channel and slow channel, add diagnostic messaging and apply custom calibration. The MLX90821 offers many automotive diagnostic features, including clamping levels, broken track diagnostics and multiple internal fault diagnostics.

The system-in-package approach uses a MEMS sensor manufactured through back-side etching. This allows the sensing element to be exposed to the vapour or other media while providing robust protection against contaminants present in harsh environments such as fuel vapour systems. The CMOS part of the system has been developed to deliver design flexibility, while the entire sensor offers exceptionally high levels of EMC protection and immunity, making it simple to design into EVAP systems for both ICE and hybrid vehicles.

Each sensor IC is calibrated during the final steps of manufacture, with the pressure transfer curve and clamping levels stored in the internal EEPROM. The measurement is provided through the ratiometric analogue output or as a SENT output, which may also contain temperature measurements. An optional NTC temperature compensation feature makes use of an external NTC, which may be required when the application also needs to record an accurate temperature measurement of the media being monitored. Further configuration is possible using software tools provided and supported by Melexis.