Hall Effect Sensors

The Hall Effect provides the capability for several non-contact magnet measurements. From speed and direction to current sensing, application requirements have driven suppliers to develop products with enhanced capability. Accurate speed and direction sensing for encoder applications dictates quite different specifications than detecting the opening action of flip, slide or clamshell covers to wake up portable handsets, PDAs and personal entertainment devices. In the first case, a precisely located dual-channel sensor provides a solution. In the second case, a single sensor with very low power consumption meets the design criteria. Taking advantage of the current sensing capabilities of Hall Effect sensors for high current sensing applications requires an entirely different approach. Here are examples of products developed to satisfy each of these applications.

Dual-Channel Sensor

Photolithography aligns the two Hall elements in Allegro MicroSystems, dual-channel Hall-Effect sensor to within 1 m. This accurate mechanical location makes them appropriate for fine-pitch detection in applications incorporating encoder ring magnet targets. The A3423 provides output signals that indicate speed and direction of the target. Spaced 1.63 mm apart, the Hall elements of the unit have a delay between direction changing and speed output transition of 2.5 sec (typical). To maintain signal quadrature, low-drift amplifiers ensure symmetry between the switches. Continuous-time offset cancellation delivers a fast start-up with a power on maximum of 5 msec, as well as providing very low output noise. Operation over a voltage range of 3.8 to 24.0V is enabled by an on-chip regulator. Initially offered in a 4-lead SIP (K) package, an SOIC-8 version is expected in the fall of this year.

http://rbi.ims.ca/5406-597

High-Current Transducer

Operating from -40 to 125C, Raztec's RAZL-1500 TAM and RAZL-1500 FAM high-current, open-loop current transducers are capable of operating under high overload conditions. Incorporating two Hall Effect magnetic field sensors arranged to give a bipolar output significantly improves the unit's immunity to external electrical noise (common mode effects) often generated by other equipment in close proximity to the transducer. The transducer's output is the difference between the two Hall signals that are provided as separate outputs to ensure improved noise rejection. Advanced electrostatic and magnetic screening reduce the interference from high-voltage switching transients and nearby current carrying conductors. This screening can remove the need for additional filtering in many applications. With a typical frequency response of 120 kHz and typical measured current of 1500A, units have a maximum I²t Rating of 3.6 × 106 A²sec and maximum measured current for 1 min of 1000A.

http://rbi.ims.ca/5406-595

Micropower Sensor

Melexis MLX90248 from its Omnipolar Micropower Hall Effect switch family operates with microwatt power consumption for portable consumer applications found in flip, slide and clamshell portable handsets, PDAs and personal entertainment devices. Using CMOS technology, the non-contact magnetic switch operates with an average current consumption of 8 µA at 2.5V and over a supply voltage range of 2.5 to approximately 3.5V. A clocking mechanism allows the Hall element and analog signal processing units to sleep in a low current state for a maximum of 70 msec and then awake for an average of 85 µs to sample any change in the magnetic field and determine if an output change is required. The sleep/awake strategy restricts the sensor's power consumption to less than 18 µW at 2.5V. To satisfy the space constraints of portable applications, the MLX90248 is available in a 1.5 × 2 × 0.43 mm Ultra-Thin QFN (Quad Flat No leads) package as well as a Thin SOT-23.

http://rbi.ims.ca/5406-596