The transfer function of a Hall device is designed with this offset between the switchpoints to filter out small fluctuations in the magnetic field that can result from mechanical vibration or electromagnetic noise in the application. The Hall effect refers to the measurable voltage present when an applied current is influenced by a perpendicular magnetic field. Following the arrows toward the right, the magnetic field becomes increasingly positive. An application using unipolar switch sensor ICs. The magnet south pole is directed towards the branded face of the device package. Digital output devices, such as the unipolar switch, reach stability with the following approximate delays:. Caution however is required because large pull-up values make it possible to induce external leakage currents to ground.

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This may also allow higher operational temperatures. The following are terms used to define the transition points, or switchpointsof Hall switch operation:.

Unipolar Hall-Effect Sensor IC Basics

Taken to the extreme, this can reduce the output voltage enough to inhibit proper external logic functions. Magnetic Switchpoint Terms The following are terms used to define the transition points, or switchpointsof Hall switch operation: The distance from the branded face to the Hall element is referred to as the “active area allegeo.

When allegto 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.

Chopper-stabilized sensor ICs allow greater sensitivity with more-tightly controlled switchpoints than non-chopped designs. Unipolar switches are described in this application note. Digital output devices, such as the unipolar switch, reach stability uipolar the following approximate delays: The gear-shift lever incorporates a magnet the red-and-blue cylinder. The line of miniature black boxes is an array of unipolar switch devices. 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.


Power-On Time Power-on time depends to some extent on the device design. Unipolar switch output characteristics. 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.

When the magnetic field again drops below B RPthe device turns off. There are hnipolar general categories of Hall-effect IC devices that provide a digital output: Yes, however bear this in mind: When the field is more positive than B OPthe device turns on. Following the arrows back toward the left, the magnetic field becomes less positive. 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 the sign indicates the polarity of the field.

This causes the output to change back to the original state. When the vehicle operator moves the lever, the magnet is moved past the individual Hall devices.

Allegro MicroSystems – Unipolar Hall-Effect Sensor IC Basics

Take this number to the derating chart in the datasheet for the package in question and check to see if the maximum allowable operational temperature must be reduced. The top panel displays switching to logic low in the presence of a strong south polarity field, and the bottom panel displays switching to logic high, also in a south polarity field.

After it has been turned-on, the unipolar IC will remain turned-on until the magnetic field is removed and the IC reverts to its off state. Most new device designs utilize a chopped Hall element. An application for detecting the position of a vehicle gear-shift lever is shown in figure 1. The north pole would then generate a positive field relative to the Hall element, while the south pole would generate a negative field.


The ultra-small Hall ICs switch as the magnet red and blue cylinder moves past them during gear-shifting. A “cleaner” signal is available when approaching from the package front side, because the Hall element is located closer to the front side the package branded face than to the back side. While the magnetic field remains more positive than B RPthe device remains turned-on, and the output state remains unchanged.

Allegro unipolar devices are listed in the selection guides on the company website, at Hall-Effect Unipolar Switches. For example, for the “UA” package, the chip with the Hall element is 0. The devices near the magnet are subjected to the magnetic field and are turned-on, but more remote devices are not affected and remain turned-off.

B can uni;olar a north or south polarity, so it is useful to keep in mind the algebraic convention, by which B is indicated as a negative value for north-polarity magnetic fields, and as a positive value for south-polarity magnetic fields.

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.