Industrial and automotive environments present many challenges for the efficient and reliable operation of electronics, and electronic Hall-effect sensor based switching is helping to simplify design and increase reliability in sensing and control circuits.
Equipment in these environments is frequently subjected to heat, humidity, and contaminants over their long operational lives, and components need to be documented for proper function over many activations and extended operational hours. Control switches are particularly susceptible to rapid wear in these environments due to their frequent use. In addition to rapidly burning through their rated activation counts, high current contact-based switches usually have accelerated degradation when loads change over time and switching currents increase. Mechanical vibrations are also common and can further amplify the rate of wear on switch contact surfaces. In extreme circumstances, these vibrations can cause the premature wear-through of protective switch coatings or cause mechanical bounce on contact closures that result in repeated current spikes and electromagnetic noise. Frequent exposure to contaminants, heat, and humidity only serve to add to wear and failure rates, even when switches are used for low current loads. When switches are used for interlocks or other safety-critical applications, the realities of this accelerated wear can require frequent maintenance checks or replacement schedules, which can increase the cost of operating and maintaining the equipment – particularly when labor costs are considered.
Hall-Effect Sensors and Switches
Fortunately, many of the shortcomings of mechanical switching can be avoided through the use of Hall-effect sensors. Hall-effect sensors detect the presence of a magnetic field by monitoring for an induced voltage in the sensor. When the magnetic field is sufficiently strong, the voltage can be used to activate a transistor and allow a current proportional to the magnetic field to flow through the sensor. Digital Hall-effect switches have additional integrated circuits that use the induced voltages to trigger a voltage output, and advanced functions can be integrated depending on the specific additional circuitry added. Common variants include simple unipolar and omnipolar digital switches, latching switches, and bipolar switches. Unipolar digital switches activate or release their outputs when a magnetic field of the correct polarity exceeds or falls below pre-set thresholds. Omnipolar switches are similar, but respond to both polarities of magnetic field direction. Bipolar latching switches will activate when a strong field of sufficient strength is sensed, but the output of the switch will stay at the switched state until the Hall-effect sensor is ‘activated’ another time by an opposite polarity magnetic field. Finally, bipolar switches typically operate by altering their output voltage up or down from a nominal output state when a positive or negative field of sufficient strength is present. Linear bipolar sensors, by extension, have a voltage output that responds linearly to the polarity of the magnetic field and the applied linear flux density.
Typical Applications for Hall-Effect Switches and Sensors
The contactless nature of digital Hall-effect switches and sensors make them ideal candidates for mechanical switch replacement in industrial and automotive environments. Because they have no moving parts, contact wear, vibration, and other physical wear out concerns are eliminated, and the lifespan of the switch becomes a function of a much more reliable hinge or other mechanical structure. Concerns with contact degradation and EMI due to arcs during large load switching also become irrelevant as switching can be handled by solid state devices, and problems with contamination can be mitigated through the use of completely sealed circuit enclosures that have no moving parts.
Industrial and automotive applications for digital Hall-effect sensors span beyond the switch replacement applications discussed above, and also include event counting, vibration control, motion damping, and current sensing. The realm of switching applications is still quite broad, however. Door or panel open/close switches are particularly easy to implement with digital Hall-effect switches, and can yield increased reliability and increase safety, particularly when used as a safety interlock. Limit switches are also an ideal candidate for the implementation of digital Hall-effect switches because of their resistance to grease and other contaminants that could be present for lubrication of the mechanism. Automotive applications of limit switches can add a nearly unlimited variety of environmental contaminants to the mix, making these sensors an even more ideal choice. Tamper detection is another frequent application. Tamper detection can be implemented as a panel switch, but sensors can also be implemented to detect the presence of external magnets that are applied in an attempt to fool a panel open/close sensor or otherwise influence the operation of secure devices. Many energy meters, for example, can be slowed or stopped through the use of strong external magnets, and digital Hall-effect sensors can detect this tampering and send alerts to upstream distribution companies. Proximity detection and docking detection are other contactless switching applications with unique advantages in automotive and industrial environments. Aftermarket vehicle-based commercial, logistics, and public safety computing applications can leverage Hall-effect-based docking detection to sense the placement of laptops or tablets in docking stations without relying on extra electrical contacts or mechanical switching. Event-counting applications can include gear position sensing in industrial automation and control applications and RPM sensing for tachometers and other rotational speed measurements. Finally, one of the more novel applications for digital Hall-effect sensors involves vibration correction and damper controls. The use of linear bipolar Hall-effect sensors yields a voltage output that varies according to the relative intensity and polarity of a magnetic field. When used with a fixed magnet, this arrangement can be used to detect vibrations or displacement along an axis, and active feedback systems can leverage the input to reduce vibrations or dampen movement. The linear nature of bipolar switches also makes them ideally suited for DC current sensing. The ability to sense DC current can also enable the transition from brushed DC motors to much more reliable brushless DC (BLDC) motors. Linear bipolar Hall-effect sensors can detect load changes and enable BLDC controls to provide efficient operation and precise speed control in an open-loop mode that does not require rotational position sensors for BLDC motor operation. Of course, unipolar, bipolar, or omnipolar Hall-effect switches can also be used for BLDC motor controllers that do leverage position sensing.
TI Hall-Effect Solutions
TI offers several digital and analog Hall-effect switches that are specifically designed for the automotive and industrial environments. The TI DRV5000 series offer superior sensitivity and excellent stability over a wide temperature range, and integrated protection features that ensure proper and reliable operation in challenging environments.
The DRV5013 Digital-Latch Hall-effect Sensor is a chopper-stabilized bipolar Hall-effect Sensor with a latching open-drain output and a current capacity of 35mA. When the sensor is in the presence of a strong south magnetic field, the sensor activates and pulls the output low until a strong north magnetic field is sensed and the output is released. Several sensitivity options are available that allow varied latch/release set points between 3.4 / -3.4 mT and 18 / -18 mT for the standard part including a higher sensitivity version designated in the device nomenclature by “FA”. An external pull-up resistor is used to generate a high-state when the output is not triggered, and a large operating voltage range of 2.5-38V is supported without the need for an external regulator. Protection functions include reverse supply protection to -22V, 40V load dump, output overcurrent, and short circuit. Operating temperature ranges from -40 to +125°C ensure compatibly with the most demanding industrial applications, and new Automotive Grade 0 AEC-Q100 variants extends the already wide temperature stability to an industry leading junction temperature of 175°C, with production line testing at 165°C. Applications include power tools, flow meters, valve and solenoid status monitors, brushless DC motors, proximity sensing, and tachometers.
The similar DRV5023 digital unipolar switch shares the output ratings and protection features of the DRV5013, but the output is driven low when a strong south pole is near the marked side of the sensor and releases when the field is removed. Activation / release sensitivity options for this part range from 6.8 / 0.5 mT to 24 / 3 mT including a higher sensitivity version designated in the device nomenclature by “FA”. The new DRV5023FI series part reverses the polarity of the output to allow redundancy in automotive applications that require dual sensors for enhanced sensing reliability.
The DRV5033 Digital-Omnipolar switch responds equally to both polarities of magnetic field direction, allowing operation without concern for the orientation of the fixed magnet being used for sensing. This can allow for variation in installation methods as well as operating in valves or other controls that do not have a limited 90-degree operational range. Four sensitivity options range from ±6.8 / ±0.5 mT to ±12 / ±1 mT including a higher sensitivity version designated in the device nomenclature by “FA”.
The line is rounded out by the DRV5053 Analog-Bipolar Hall-effect Sensor. This high-sensitivity sensor offers unique functionality as the output normally rests at 1V, and can vary up or down to 2V or 0V depending on the polarity and strength of the magnetic pole near the marked side of the package. Six different sensitivity options between -11mV/mT and 45mV/mT are available, and the output is stable to ± 10% over a wide -40 to 125°C operating range. This cost-differentiated sensor provides an inexpensive solution for accurate sensing in flow meters, docking adjustment, vibration correction, and damper controls.
All of TI’s DRV5000 series feature pin-compatible SOT-23 or TO-92 packages, 2.7-38V operation, reverse polarity protection to -22V, and stability over a wide temperature range of -40 to 125°C. Automotive rated parts extend the operational temperature spec to 150°C with AEC-Q100 qualification, and provide load dump protection to 40V and overcurrent protection to prevent damage if the output is shorted to ground. 
TI Hall-Effect Technical Resources
TI has provided several technical references that provide excellent starting points for new designs implementing these Hall-effect sensors and switches. The extended battery life sensor technical paper details methods for pairing the TI DRV5000 series Hall-effect sensors with TI’s MSP430 CPU to enable physical presence detection systems for door or window security and energy meters. This ultra-low power consumption design can operate for decades off of low-cost CR2032 coin cells. A speed-controlled 24V brushless DC outrunner motor reference design implements closed-loop speed control to provide efficient operation and maintain an exact RPM speed across a load torque profile. The 6x6x3 cm motor design natively operates at 2054 RPM, but motor speed and maximum current can be easily tuned by changing resistors in the design. Several automotive resources are also available. The TIDA-00281 Automotive 48V 1kW Motor Drive Reference Design is a 3-Phase Brushless DC Motor Drive designed to operate in 48-V automotive applications. DRV5013 Hall-effect sensors are leveraged in the design to enable speed control. The TIDA-00875 BLDC pre-driver reference design also leverages TI DRV5013 Hall-effect sensors to enable a standard brushed motor driver to be adapted for use with a with brushless DC motors. The design features BLDC speed control, a 12 to 24V operating supply voltage, and can drive motors with 2.8 or 20A of peak current, depending on the motor driver implemented. The dry double-clutch transmission solutions page contains links to the parts and reference designs needed for several automotive double-clutch transmission systems, and the Brushless DC Control System solutions page contains BLDC motor driver sub-system designs, application notes, and numerous other resources to assist in the design of BLDC motor drive systems.