5 Selecting the right part for limit detection

Selecting the right part for limit detection

Hall switches for limit detection are often selected based on the following specifications:

• B_OP and B_RP: The B_OP or B_RP determine the implemented limit, as described in the previous sections. The necessary values of these specs depend on the strength and size of the magnet as well as its distance from the sensor. A tighter hysteresis between B_OP and B_RP enables detecting smaller distance openings for case tamper detection.
• Current consumption: If the application runs off a battery, the current consumption should be minimized to maximize the lifetime of the battery.
• Response time: Quick response times require a fast sampling rate.
• Operating voltage range: Different systems have different available supply voltages. If the available supply voltages of a system are all outside of the operating voltage range of the Hall position sensor, an additional voltage regulator device will be needed to generate a voltage rail for powering the Hall position sensor.
• Open-drain vs push-pull output: Open-drain outputs are selected when it is desired to have the logic high output voltage to be at a different voltage than the VCC voltage of the Hall position sensor or if it is necessary to implement a logical AND of different open-drain outputs without additional circuitry. Compared to open drain outputs, push-pull outputs have lower current consumption and do not require a pullup resistor.
• Omnipolar vs. Unipolar: Omnipolar Hall sensors detect both the North and South poles of a magnet while unipolar only detects one.

The DRV5032 is offered in multiple versions, making this device ideal for limit detection. The various B_OP and B_RP threshold variants of the DRV5032 enable multiple options for the magnetic flux density limit. In addition, the device has open-drain output, push-pull output, omnipolar, and unipolar device variants. Also, the device has a low average current consumption and can be powered from low voltages, which maximizes the lifetime of any battery that powers it.

If it is necessary to sense in three directions, such as for electricity meter magnetic tamper detection, a 3D linear Hall position sensor can also be used. Some 3D linear Hall devices like the TMAG5170 and TMAG5273 include a feature where a limit can be configured by the user for each axis so that the Hall sensor can provide an interrupt when the sensed magnetic flux density of any axis is beyond its set limit.

Alternate Device Recommendations

For high-speed end of travel applications, a fast response time is needed, which can be achieved with the DRV5021, DRV5023, or DRV5033 Hall switches. The TMAG5124 can also be used for remotely detecting an end of travel event. Table 5-1 has links that provide more details on the specifications of these alternate devices: