Note that the south pole of the magnet colored red is toward the Hall devices, and that the Hall devices are oriented with the branded face of the device toward the magnet south pole. Typical Operation When a unipolar switch turns on, the resulting output signal can be either at logic high or logic low, depending on the design of the device IC output stage. Most new device designs utilize a chopped Hall element. Following the arrows back toward the left, the magnetic field becomes less positive. Chopper-stabilized sensor ICs allow greater sensitivity with more-tightly controlled switchpoints than non-chopped designs.
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The line of miniature black boxes is an array of unipolar switch devices. Chopper-stabilized sensor ICs allow greater sensitivity with more-tightly controlled switchpoints than non-chopped designs. The devices near the magnet are subjected to the magnetic field and are nuipolar, but more remote devices are not affected and remain turned-off. An application for detecting the position of a vehicle gear-shift lever is shown in figure 1.
This convention allows arithmetic comparison of north and south polarity values, where the relative strength of the field is indicated by the absolute value of B, and uipolar sign indicates the polarity of the field. This causes the output voltage to change to the opposite state either to high or to low, depending on the device design.
Unipolar Hall-Effect Sensor IC Basics
Here the device is off, and the output voltage V OUTon the vertical axis depends on the device design: The branded face is where you will find the identification markings of the device, such as partial part number or date code. This is not a device problem, rather the leakage occurs in the conductors between the pull-up resistor and the device unipopar pin.
A single magnet presenting a south polarity positive magnetic field of sufficient strength magnetic flux density will cause the device to switch to its on state. Magnetic Switchpoint Terms The following are terms used to define the transition points, or switchpointsof Hall switch operation: The minimum pull-up resistance is a function of the Hall Allegroo maximum output current the devices usually are designed to sink current and the supply voltage.
Unipolar Hall-effect sensor ICs, often referred to as “unipolar switches,” are operated by a positive magnetic field. The Hall effect refers to the measurable voltage present when an applied current is influenced by a perpendicular magnetic field. There are four general categories of Hall-effect IC devices that provide a digital output: Note that the south pole of the magnet colored red is toward the Hall devices, and that the Hall devices are oriented with the branded face of the device toward the magnet south pole.
The transfer function of a Hall device is designed with this offset between the switchpoints qllegro filter out small fluctuations in the magnetic field that can result from mechanical vibration or electromagnetic noise in the application. The north pole would then generate a positive field relative to the Hall element, while the south pole would generate a negative field.
Allegro MicroSystems – Unipolar Hall-Effect Sensor IC Basics
Unilolar switch output characteristics. Taken to the extreme, this can reduce the output voltage enough to inhibit proper external logic functions. Yes, however bear this in mind: Digital output devices, such as the unipolar switch, reach stability with the following approximate delays: The distance from the branded face to the Hall element is referred to as the “active area depth.
Power-On Time Power-on time depends to some extent on the device design. This causes the output to change back to the original state.
A very strong field will not damage an Allegro Hall-effect device nor will such a field add additional switchpoint hysteresis other than the designed hysteresis. The following are terms used to define the transition points, or switchpointsof Hall switch operation:. When the vehicle operator moves the lever, the magnet is moved past the individual Hall devices. Following the arrows back toward the left, the magnetic field becomes less positive. For example, for the “UA” package, the chip with the Hall element is 0.
Caution however is required because large pull-up values make it possible to induce external leakage currents to ground.
While the magnetic field remains more positive than B RPthe device remains turned-on, and the output state remains unchanged. When the magnetic field again drops below B RPthe device turns off. Unipolar switches are described in this application note.
Digital output devices, such as the unipolar switch, reach stability with the allfgro approximate delays:. These currents could be high enough to reduce the output voltage, regardless of the state of the magnetic field and device switching state.