Pressure sensor for automotive applications such as EV thermal management

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

At the heart of the MLX90834 is Melexis’ Triphibian technology. This MEMS sensor design allows for accurate pressure measurements in both gas and liquid media, even at pressures up to 70 bar. This versatility is achieved through a unique construction featuring a suspended cantilever with a diaphragm at its tip, all housed within a compact SO16 package.

Heat pump systems require careful monitoring of both the pressure and temperature of the refrigerant. To prevent damaging the most expensive component in the system, it is critical to prevent 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 outlet of the evaporator. This is achieved by precisely monitoring the pressure and temperature at the same spot between the evaporator and compressor, allowing the system to accurately calculate and regulate the degree of superheat of the fluid by using smart expansion valves.

The implementation of a Triphibian sensor utilising digital SENT allows the system to obtain precise pressure and temperature data. The MLX90834 can interface with external NTCs and the provided factory calibration achieves an accuracy better than ±1oC in extended temperature ranges. The accurate pressure measurement is used to derive the equivalent temperature of the media when present in saturation (= co-existence of liquid and gas in the evaporator) while the NTC provides 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 significantly benefit from the MLX90834’s features. By embedding this digital sensor within heat pump components like valves, manufacturers can create more intelligent valves with edge computing capabilities. 

Melexis’ motor driver ICs can be used to process data from the MLX90834. This allows heat pump manufacturers to integrate system regulation directly into their components, enhancing their value proposition.

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

The MLX90834 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 Digital Signal Processing (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. The MLX90834 has been developed as a Safety Element out of Context (SEooC) under ISO 26262, enabling up to ASIL C system integration ensuring it meets the latest EV safety demands.