Digital output pressure sensor designed for automotive applications

Melexis has expanded its Triphibian family with the MLX90834 pressure sensor, developed for automotive applications such as EV thermal management. This robust, factory-calibrated MEMS solution accurately measures pressure in gas and liquid media from 2 to 70 bar. Its digital SENT output supplies absolute pressure information, diagnostic and temperature data, enabling improved system performance and reliability.

At the heart of the sensor is the company's ground-breaking Triphibian technology. This innovative MEMS sensor design permits accurate pressure measurements in gas and liquid media, even at pressures up to 70 bar. This versatility is attained through a unique construction featuring a suspended cantilever with a diaphragm at its tip, all housed within a compact SO16 package.

Heat pump systems need careful monitoring of the pressure and temperature of the refrigerant. To stop damaging the most expensive component in the system, it is crucial to stop liquid media from getting at the inlet of the compressor. For that purpose, the system must ensure that the refrigerant is always in a superheated gas state when reaching the evaporator outlet. This is accomplished by precisely monitoring the pressure and temperature at the same spot between the evaporator and compressor, enabling the system to accurately calculate and regulate the degree of superheat of the fluid by using smart expansion valves.

Implementing a triphibian sensor using digital SENT enables the system to obtain precise pressure and temperature data. The sensor can interface with external NTCs, and the provided factory calibration achieves an accuracy better than ±1C in extended temperature ranges. The accurate pressure measurement is utilised to derive the equivalent temperature of the media when present in saturation (= co-existence of liquid and gas in the evaporator) while the NTC supplies the actual temperature of the fluid, with the difference between the two corresponding to the amount of superheat achieved in the fluid.

Smart expansion valves greatly benefit from the sensor's features. Manufacturers can create more intelligent valves with edge computing capabilities by embedding this digital sensor within heat pump components like valves. Employing the company's expertise in sensing and driving technologies, its motor driver ICs can be employed to process data from the sensor. This enables heat pump manufacturers to integrate system regulation directly into their components, improving their value proposition.

Ultimately, these intelligent, locally controlled expansion valves, with increased accuracy in pressure and temperature sensing, allow heat pump systems to operate with less overheating, leading to improved overall efficiency.

The device includes a sensor readout circuit, digital hardware, voltage regulators, and digital output drivers. Piezo-resistive elements implanted into the membrane create a Wheatstone bridge to generate an input signal. This signal is amplified and converted into a digital format, allowing the 16-bit DSP to apply temperature compensation before providing the result as a digital output (SENT).

The sensor is equipped with advanced protective mechanisms against overvoltage (above +40V) and reverse voltage (below -40V), making it suitable for automotive and truck applications. It has been developed as an SEooC under ISO 26262, enabling up to ASIL C system integration, ensuring it meets the latest EV safety demands.

"Our new MLX90834 is, at its very core, a truly versatile and operationally efficient option for a wide variety of heat pump applications," said Laurent Otte, product line director at Melexis. "By leveraging our ground-breaking Triphibian™ technology to create a pressure sensor with such flexibility, programmability and intelligence, our talented engineers are continuing to meet the evolving requirements of our customers."