Using the latest MEMS technology closely integrated with an analogue signal chain and digital signal processing, the MLX90821 is a system-in-package IC solution designed to provide reliable measurement of fuel vapor pressure as low as 50 mbar and up to 700 mbar - making it suitable for EVAP systems designed for internal combustion engine or hybrid vehicles.
Implementing fuel pressure vapor 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 vapor to the atmosphere. As vapor builds up inside fuel tanks and crank cases, the EVAP systems are designed to capture, store and responsibly dispose of the vapor, 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.
Fuel vapor 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 high level of integration provided through the system-in-package approach makes designing with the MLX90821 extremely simple, providing what is essentially a ‘plug & 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 vapor or other media while providing robust protection against contaminants present in harsh environments such as fuel vapor 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.
