Switches


reduces size and weight. Some of the automotive applications where these features are essential include: ● Power steering motors ● Chassis positioning ● Dual-clutch transmissions ● Traction motor positioning in hybrid- electric and fully electric vehicles ● Steering angle detection The lower weight of Hall sensors assists car manufacturers in reducing fuel consumption, while the smaller size improves mechanical design flexibility. While the appeal of using Hall-sensor technology for automotive applications is obvious, the automotive industry has specific requirements about quality, reliability, and safety for safety-critical functions, prohibiting commodity and general-purpose Hall sensors. These cover:


Quality


Safety certifications and the Automotive Engineering Council’s standards specify the exact requirements for repeatability, traceability, and production quality. These apply not just to individual components, but also to the complete sensor system assembly.


Under each of these headings, general- purpose Hall sensors do not conform to the automotive sector’s typical performance specifications, meaning these general sensors potentially expose automotive OEMs to an elevated risk of failure. Some general-purpose magnetic position sensors previously installed in production vehicles presented reliability issues and safety concerns for vehicle manufacturers. The leading cause of problems is external magnetic interference. Automobiles are electrically noisy environments with many stray magnetic fields that can distort the signal sensed by the IC, interfering with the operation of a magnetic sensor. This can cause measurement errors that impact the accuracy of the sensor’s position readings. In an EV traction motor, for example, these errors could lead to a severe reduction in or even a complete loss of torque or unpredictable wheel rotation.


Reliability


Devices used in critical automotive applications are expected to operate in a wider temperature range than that expected for consumer or industrial devices. They are also specified to operate over a minimum lifetime of ten years. Issues have arisen about the repeatability of assembly production. Hall sensors measure position relative


www.cieonline.co.uk Figure 3. A current output is more resilient than voltage in the presence of noise spikes


to a paired magnet mounted on the motor shaft, which rotates relative to a static sensor with a small air gap between them. Some manufacturers have faced quality problems achieving assembly tolerances during production.


Safety


The use of magnetic position sensors has also been reviewed following the adoption of the ISO 26262 functional safety standard. This standard requires a rigorous Failure Modes Effects and Diagnostic Analysis (FMEDA) to be performed at the system level, and to


implement adequate safety countermeasures in combating the risks associated with known failure mechanisms. Commodity magnetic position sensors do not have the features required to guarantee system safety during a device failure, and are also not supported by ISO 26262-compliant development, production processes, and documentation.


Automotive-qualified Hall-sensor switches/latches


The DIODES AH32xxQ series of two-wire, Hall-sensor, unipolar switches and latches by Diodes Incorporated is based on an


advanced design that enables automotive systems manufacturers to achieve ISO 26262-compliant position- and proximity- sensing systems. These ICs are AEC-Q100 qualified, manufactured to the highest standards in IATF 16949-certified sites, and have supporting PPAP documentation. They also provide high sensitivity (AH3270Q/71Q & AH3280Q/81Q) and robustness (8kV ESD withstand capability). These sensor ICs require only two wires, reducing overall system cost in especially long- wire harnesses. Unlike most Hall-sensor switches (which have a voltage output), these devices provide a current output that is more resilient than the voltage in the presence of noise spikes (Figure 3). For flexibility, they have been designed to operate over a wide voltage range (2.7V to 27V) and are supplied in industry-standard SC59 and SIP-3 packages.


Integrated self-diagnostic functions (AH324xQ and AH328xQ) make them ideal for ASIL-compliant systems, which require high levels of functional safety (Figure 4). These features operate in the background without external activation. If an error is detected, the device enters a “safe mode” of operation where the output (supply) current drops to 1mA, serving as a warning flag to the rest of the system. In addition, the integrated self-diagnostics monitor supply voltage and temperature, and self- tests major functional blocks.


Conclusion


Vehicle electrification is a significant driver behind the growing number of motors in automobiles, which in turn is creating the requirement for a small, lightweight, reliable, and low-cost sensor to track their speed and position. Magnetic position and proximity sensors based on the Hall effect offer such a solution; however, commodity versions are unsuitable for automotive applications because they do not allow position-sensing systems to meet critical safety standards like ISO 26262. The AH32xx range of Hall switches/ latches by Diodes Incorporated has been specially designed to have a wide operating voltage range to increase their sensitivity and current output signaling to improve robustness in the presence of voltage spikes. Some devices in this family also include self-diagnostic features which enable sensor subsystems to achieve the safety certifications required for automotive applications.


Figure 4. Functional diagram showing self-diagnostic features of the AH324xQ/AH328xQ www.diodes.com Components in Electronics April 2023 45


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