SLYA051B October 2020 – May 2024 DRV5055 , DRV5055-Q1 , DRV5057 , DRV5057-Q1 , TMAG5170 , TMAG5170-Q1 , TMAG5170D-Q1 , TMAG5173-Q1 , TMAG5273
Position sensing in mechanical systems using Hall-effect magnetic sensors allows precise control while also providing contact free feedback. This increases overall reliability and durability. Since magnetic fields are able to permeate most materials, the sensor can be placed so that it is protected and isolated from other moving parts of the system. This allows for a great deal of flexibility of design. Hall sensors can be used in detecting angular position, angular rotation speed and direction, proximity, and even absolute position. When moving a magnet along a path, some applications require determination of absolute position. This application note covers how to implement this type of design for long stroke movement where it is necessary to use multiple sensors in a linear array.
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The best Hall-effect sensor for any given application depends on the type of motion being detected and the various mechanical limitations of the system. Latches and switches operate relative to a fixed threshold. When the sufficient magnetic field is present, the outputs state of these devices changes. Linear sensors however produce a variable output relative to the input magnetic field. Latches and switches are primarily useful where discrete fixed operating positions are used. For example, you might detect the closure of a lid or setting of a 3 position switch using a single DRV5032. Linear Hall-effect sensors are typically needed where absolute position or fine control is required, such as tracking the fluid level in a tank, dial or slider state, or seat adjustment setting.
Selecting a linear Hall-effect sensor depends on system constraints. In the case of long stroke linear transit, the following devices offer design flexibility to suit the application each can provide an appropriate design.
| Device | Axis of Sensitivity | Output Mode | Package Options | Automotive Grade Available |
|---|---|---|---|---|
| DRV5055 | Z | Analog | SOT-23, TO-92 | ✓ |
| DRV5057 | Z | PWM | SOT-23, TO-92 | ✓ |
TMAG5170, | X, Y, Z | SPI | VSSOP | ✓ |
| TMAG5173-Q1 | X,Y,Z | I2C | SOT-23 | ✓ |
For simple applications, DRV5055 and DRV5057 can be quickly implemented, and their outputs update immediately upon change in magnetic flux density. However, both of these devices are constrained mechanically due to only having sensitivity along a single axis. TMAG5170 and TMAG5173-Q1 offers three integrated sensors with each sensor oriented along a different axis. This allows the greatest flexibility in system design, and allows the user to observe the entire magnetic flux density. Upon completing each conversion TMAG5170 transmits the resulting digital code over SPI and TMAG5173-Q1 transmits the resulting digital code over I2C, which eliminates the need for an ADC to convert the output signal in both of the device.
In every case, the number of sensors required to implement a linear transit design is primarily dictated by magnet length and the total travel distance. Magnet strength and distance from the sensor also impact the quality of measurement. Fortunately, there is a simple algorithm that scales easily in this application that can be used to determine position of a magnet with an array of sensors.
This discussion demonstrates a basic design procedure focused around DRV5055. The observations and principles discussed apply equally to the DRV5057, TMAG5170 and TMAG5173-Q1. The TMAG5170D-Q1 is a dual-die version of the TMAG5170 that can be used in a system where redundancy is required.