By Andy Choi
Melexis has developed integrated MEMS sensors, such as the MLX90808 and the MLX90807 with CMOS technology and MEMS bulk micromachining, which are completely automotive qualified.
Both sensors include a silicon membrane with piezo-resistors, which would radically change the stress stimulated by pressure into an electric signal. Full calibration on chip is allowed by an analog signal chain, which interacts with a digital core that includes programmable memory and helps to attain an optimized transfer function within the boundaries of the desired temperature and pressure range.
The integrated pressure sensor die can work under a pressure that ranges from 100mbar to several bars. When the media which is to be measured is relatively benign, such as dry air in barometric sensing or brake boosters, engine intake manifolds or even when the media is stronger like the fuel vapor, these sensors could be used directly. However, in harsher media applications such as engine exhaust gas, liquids and oils, special and secondary protection for the die are integrated inside the Melexis chips.
The sensors have proved their mettle in taxing automotive applications and they not only meet but also surpass the typical quality standards set by the automotive industry. They exhibit high level of accuracies after calibration in applications that need a compact and tiny pressure sensor solution. These sensors are completely programmable via the connector with its built in protection against all overvoltage automotive conditions. Circuitry that could handle all automotive diagnostic needs such as short and open circuit conditions and broken membrane detection is provided in the sensors.
The devices are capable of addressing a number of deficiencies, which are found in other competing integrated sensors. According to Laurent Otte, the Product Marketing Manager in Melexis, the experimental data obtained from stress tests indicate that both the MLX 90807 and 90808 have the capacity to cycle the MEMS diaphragm several times more than the standard test limits without failures. These results would help designers to confidently utilize the sensors in high reliability applications, secure in the knowledge that the chips could handle the pressure and also that in the event of failure the chip could communicate through diagnostics and facilitate safe error handling.
The sensors also include features such as the on-chip signal conditioning, 5 V analog ratio-metric output, output that is proportionate to pressure conditions, less than 1% error range typical overall and rail to rail output.