Sensor Solutions That Stand Up to the Rigors of Automotive Apps

By Carolyn Mathas

Contributed By Hearst Electronic Products


It is amazing to think that in 1995 approximately 10 sensors were used in automotive engine control applications. By 2012, that number grew to more than 30. The use of sensors under the hood in automobiles and trucks has blossomed due to safety requirements and a trend toward improved operating efficiency, lower emissions, and reduced fuel consumption. Add in another fast-growing part of the automotive environment, infotainment, and the total automotive sensor market is expected to reach $33.59 billion by 2022, at a CAGR of 7.8 percent.

As the number of intelligent systems in cars and trucks grows, and as customers demand comfort, infotainment and fuel efficiency, the number of sensors and the level of sensor fusion and integration will skyrocket. In terms of units, the number of sensors in automotive use is expected to reach 8.93 billion units in 2022, up from 2.965 billion units in 2012, representing an estimated CAGR of 11.7 percent from 2013 to 2022, according to a new market research report: “Sensors Market for Automotive Applications 2012 – 2022,” published by MarketsandMarkets.

Sensors are fulfilling many important tasks in vehicles, ranging from engine performance and passenger safety to comfort and vehicle dynamic behavior. The future of automotive sensor advancement is highly dependent on sensor technologies such as MEMs, wireless sensors, radar, and many more.

Government regulations in North America, Europe, Japan, China, and South Korea continue to drive demand for safety features that range from passive to integrated active and passive safety systems. These developments are behind the growth of applications to assist drivers and keep them safe. Engine management, occupant comfort, convenience and entertainment, and advanced driver-assistant systems are evolving rapidly. The use of networking is also increasing as various subsystems communicate internally within vehicles and with external devices and networks. Never has demand for and reliance on automotive sensors been so great.

Clearly there are numerous sensors and sensor-based systems used in automotive applications. Of all of these, we have selected three noteworthy parts that are especially representative of the type of automotive sensors in use today. Keep in mind that these parts, as others designed for automotive use, are being continuously upgraded and redesigned for maximum efficiency, ever smaller size, and to consume substantially lower power.

The SS360PT/SS460P High Sensitivity Latching Digital Hall-Effect Sensor IC (Figure 1) with built-in pull-up resistor by Honeywell is used in such automotive and industrial applications as flow-rate sensing, speed and RPM sensing, tachometer, counter pickup, and for motor and fan control. The sensor operates using the magnetic field from a permanent magnet or electromagnet, and responds to alternating North and South poles.

The pull-up resistor can eliminate the need for external components to reduce cost.

Honeywell SS350PT/SS460P high-sensitivity latching digital Hall-Effect sensor block diagram

Figure 1: The Honeywell SS350PT/SS460P high-sensitivity latching digital Hall-Effect sensor block diagram.

This sensor IC does not use chopper stabilization on the Hall element, providing a clean output signal and a faster response time when compared to competitive high- sensitivity Hall-Effect bipolar latching sensor ICs which do use chopper stabilization.

The SS350PT/SS460P operates from only 30 Gauss typical, at 25°C [77°F] and 55 Gauss maximum over the full -40°C to 125°C [-40°F to 257°F] temperature range, allowing for the use of small magnets or a wider air gap. Its internal pull-up Hall IC design keeps component cost down and simplifies installation, and bipolar latching magnetics provide for accurate speed sensing and RPM measurement. It features a robust design, and its RoHS-compliant material meets directive 2002/95.

The MEMSIC MXR7900A/C/D (Figure 2) is a low-cost, high-performance ±1.0 g dual-axis accelerometer with ratiometric outputs that is fabricated on a single CMOS IC. It measures acceleration with a sensitivity of 900 mV/g and provides a g-proportional ratiometric analog output above/below the zero-g point at 50 percent of the supply voltage.

The unique design is based on heat convection and needs no solid proof mass, eliminating the typical problems associated with competitive devices. A single heat source, centered in the silicon chip, is suspended across a cavity. Equally-spaced aluminum/polysilicon thermopiles (groups of thermocouples) are located equidistantly on all four sides of the heat source (dual axis). Under zero acceleration, a temperature gradient is symmetrical about the heat source so that the temperature is the same at all four thermopiles, causing them to output the same voltage.

Acceleration in any direction will disturb the temperature profile, due to free convection heat transfer, causing it to be asymmetrical. The temperature, and hence voltage output of the four thermopiles, will then be different. The differential voltage at the thermopile outputs is directly proportional to the acceleration. There are two identical acceleration signal paths on the MXR7900A/C/D; one to measure acceleration in the x-axis and one to measure acceleration in the y-axis.

Memsic MXR7900C

Figure 2: The Memsic MXR7900C is used in automotive rollover applications.

It can measure both dynamic acceleration such as vibration and static acceleration, such as gravity. It also provides a shock survival greater than 50,000 g. The device assures significantly lower failure rates and lower loss due to handling during assembly and in the field. For automotive applications, it is used for rollover sensing, VSC/EPS applications.

Other features include:
  • Monolithic design with mixed-mode signal processing
  • RoHS compliance
  • On-chip sensitivity compensation for temperature variations
  • On-Demand Self-Test
  • 900 V/g sensitivity
  • Independent axis programmability (optional)
  • Resolution of better than 1 mg
  • 19 Hz bandwidth
  • >50,000 g shock survival rating
  • 4.50 to 5.25 V single-supply operation
  • Small surface-mount package at 5 x 5 x 2 mm

Another prime example is the STMicroelectronics AIS329DQ, a high-performance, ultra-low-power three-axis accelerometer with digital output for automotive applications (Figure 3).

STMicroelectronics’ AIS329DQ accelerometer

Figure 3: STMicroelectronics’ AIS329DQ accelerometer performs many functions within automotive design.

Features include a wide supply voltage range of 2.4 V to 3.6 V, low-voltage compatible IOs (1.8 V), ultra-low-power mode consumption down to 10 μA, ±2 g/±4 g/±8 g dynamically-selectable full scale, an SPI / I2C digital output interface, 16-bit data output, two independent programmable interrupt generators, a system sleep/wakeup function, and high-shock survivability (of up to 10,000 g).

The AIS328DQ is capable of measuring accelerations with output data rates from 0.5 Hz to 1 kHz. The AIS328DQ also may be set to a low-power operating mode, characterized by lower data rate refreshments. In this way the device, even if sleeping, continues to sense acceleration and to generate interrupt requests.

The device’s ultra-low-power operational modes allow advanced power saving and smart sleep-to-wake-up functions. When the sleep-to-wake-up function is activated, the AIS328DQ is able to automatically wake up as soon as the interrupt event has been detected, increasing the output data rate and bandwidth.

The AIS328DQ may also be configured to generate an inertial wake-up and free-fall interrupt signal based on a programmed acceleration event along the enabled axes. Both free-fall and wake-up can be available simultaneously on two different pins.

A self-test capability allows the user to check the functioning of the sensor in the final application. Available in a small quad flat pack no-lead package (QFPN) with a 4 x 4 mm footprint, the AIS328DQ responds to the trend toward application miniaturization, and is guaranteed to operate over a temperature range from -40 to +105°C.

This accelerometer is used in such applications as in-dash car navigation, tilt/inclination measurement, anti-theft devices, intelligent power saving, impact recognition and logging, vibration monitoring and compensation, and motion-activated functions.

The automotive industry will only become more exciting for engineers involved in sensor development or application. For safety reasons, as well as convenience, the human factor is reduced and more is put into the hands of highly intelligent and aware sensor-based systems. For more information on the parts discussed in this article, use the links provided to access product information pages on the Digi-Key website.
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