Allegro Hall-Effect Sensor ICs
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Product Information Allegro Hall-Effect Sensor ICs By Shaun Milano Allegro MicroSystems, LLC Allegro™ MicroSystems, LLC is a world leader in developing, manufacturing, and marketing high-performance Halleffect sensor integrated circuits. This note provides a basic understanding of the Hall effect and how Allegro designs and implements Hall technology in packaged semiconductor monolithic integrated circuits. Hall Effect Principles The Hall effect is named after Edwin Hall, who in 1879 discovered that a voltage potential develops across a currentcarrying conductive plate when a magnetic field passes through the plate in a direction perpendicular to the plane of the plate, as illustrated in the lower panel of figure 1. The fundamental physical principle behind the Hall effect is the Lorentz force, which is illustrated in the upper panel of figure 1. When an electron moves along a direction, v, perpendicular to the applied magnetic field, B, it experiences a force, F, the Lorentz force, that is normal to both the applied field and the current flow. In response to this force, the electrons move in a curved path along the conductor and a net charge, and therefore a voltage, develops across the plate. This Hall voltage, VH , obeys the formula below, which shows that VH is proportional to the applied field strength, and that the polarity of VH is determined by the direction, either north or south, of the applied magnetic field. By this property, the Hall effect is employed as a magnetic sensor. VH = Lorentz Force → → → F=qv×B Figure 1. The Hall effect and the Lorentz force. The blue arrows, B, represent a magnetic field passing perpendicularly through the conductive plate. VH is the Hall voltage across the conductive plate, I is the current passing through the plate, q is the magnitude of the charge of the charge carriers, ρn is the number of charge carriers per unit volume, and t is the thickness of the plate. Allegro semiconductor integrated circuits integrate a Hall element, as the Hall effect applies to both conductive plates and semiconductor plates. By using the Hall effect in a fully integrated monolithic IC it is possible to measure magnetic field strength and create a vast array of Hall-effect integrated circuits for many different applications. An Allegro Hall switch is activated by a positive magnetic field that is generated by a south pole. A positive field will turn on the output transistor and connect the output to GND, acting as an an active low device. The field required to activate the device and turn on the output transistor is called the magnetic operating point, and is

abbreviated BOP. When the field is removed the output transistor is turned off. The field required to turn off the device once it is activated is called the magnetic release point, or BRP. The difference between BOP and BRP is called the hysteresis and is used to prevent switching bounce due to noise. Allegro also makes magnetic latches and linear devices. Magnetic latches switch on with a south pole (BOP) and switch off with a north pole (BRP). Requiring a north pole to deactivate the latch separates latches from simple switches. Because they do not switch off when the field is removed,...

ferromagnetic targets. However complex the sensor topology, the components are all manufactured in and on the surface of a thin substrate of a semiconductor material. Allegro devices are manufactured on silicon substrates, by doping directly into the silicon with different materials to create n-type (electron) or p-type (electron hole) carrier regions. These n-type and p-type material regions are formed into geometries that make up the active and passive components of the integrated circuit, including the Hall element, and are connected together by depositing metal over the geometries. In...

For production efficiency, these circuits are grown in the substrate while it is still in the form of a large wafer. The circuits are repeated in a pattern of rows and columns that can be sawn into individual die, or “chips,” as illustrated in figure 5. A single Allegro Hall-effect sensor IC device can be seen in figure 6. This is the simple switch with functional block diagram as shown in figure 2. All of the circuitry is included on the IC, including the Hall element which can be seen as the red square in the middle of the chip, as well as the amplifier circuitry and protection diodes and...

die is seen inside the case, mounted on a copper die pad. Contact to the copper leads is made through gold wire-bonding from metal pads on the die surface to the electrically isolated package leads. The package is then encapsulated, or overmolded, with plastic to protect the die from damage. The package in figure 7 is the simple switch of figure 2 with VCC, GND, and an Output leads in a miniature 3-pin single inline package (SIP). Other packages can be seen in figure 8 and include a wafer-level chip scale package (CSP), an SOT23W, an MLP, a 3-pin UA-package SIP, and a 4-pin K-package SIP....