Switches
Understanding the demands on hall sensors for automotive applications
By Charles Kuo, sensor product line manager, Diodes Incorporated T
he demand for compact, accurate position sensors in automotive applications will grow substantially to $1.6 billion by 2026, in line with the growth in electric
vehicles (Figure 1). These sensors track the rotor’s position inside the motor responsible for traction, power steering, and windows; ensuring control and safety coverage. First, this article reviews legacy approaches to proximity, position detection, and their limitations. It then considers the operation and advantages of magnetic proximity and position sensors, based on the Hall effect, before discussing the factors which limit their use in automotive applications. Finally, it presents a series of Hall-sensor switches/ latches that enable automotive systems to achieve the highest levels of automotive safety certification: ISO 26262.
Problems with legacy position- sensing technologies Potentiometers, optical encoders, and resolvers were most widely used for position- sensing, but each has shortcomings that impact their use in automotive applications. Potentiometers use physical contact to measure rotary motion. However, this means they are subject to mechanical wear and tear caused by friction, and performance can be affected by shock or vibration. In addition, contamination of the resistive element by
of the embedded magnetic field. As this varies, the potential difference across the sensor changes, and this can be used to track changes in an external magnetic field. For example, simple magnetic switches detect the opening and closing of a window or door (Figure 2) using a Hall sensor and a magnet on either side of the locking mechanism.
Figure 1. Vehicle electrification is driving the demand for position and proximity sensors
foreign substances like dirt, dust, moisture, or grease can impair performance and even lead to premature failure. Optical encoders measure position by detecting alternating light and dark areas as a disk with cut-out holes (often called a code wheel) rotates between an LED light source and a photodiode sensor. They are vulnerable to contamination however, which lowers reliability by interfering with the light source and detector. Another disadvantage of optical encoders is that they are bulky (a problem in space-constrained automobiles) and must be assembled precisely to have very low tolerances.
Resolvers use an electromagnetic transducer to measure position at high rotational speeds. While they are accurate, they are large and heavy, which increases costs and furthers incompatibility with small-space automotive applications.
Magnetic sensors—smaller, lighter, and lower cost
Hall-effect (or Hall) sensors (Figure 2) typically include one or more embedded magnetic elements. When an external magnetic field comes into the proximity of the sensor, it alters the polarity and strength
Hall-sensor technology evolved to enable precise and accurate linear- and rotary-positioning measurements in many applications. A rotary position sensor can be implemented using a simple assembly, consisting of a fixed sensor board mounted perpendicular to a rotating magnet mounted on-axis on the shaft of the rotor. Manufacturers developed the capability to produce Hall sensors in an integrated circuit (IC) on a standard, complementary metal-oxide semiconductor (CMOS) fabrication process, making their high- volume production more cost-effective. Therefore, magnetic position sensors are smaller, lighter, and less expensive than other sensor technologies.
Automotive requirements for the use of Hall sensors
Instead of using mechanical or hydraulic actuation, electronic control in functions like steering and gear change improves performance, increases reliability, and
Figure 2. Hall sensors controlling a motor to open/close a car window 44 April 2023 Components in Electronics
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