TMAG5170-Q1: Linear 3D Hall vs. 1D Hall-effect Sensor

Dajon,

One of the major benefits of the 3D sensor is that it has much greater flexibility than then 1D when is comes to placement.  When tracking angle position with a 1D, you must have two sensors each placed 90 degrees apart at the same distance.  Depending on the package type this can be done with the sensors coplanar to the center of the magnet or slightly offset in an off-axis (or out-of-plane) position.  

The 3D sensor allows for a single device to measure the two field components needed for angle measurements and may be placed anywhere about the magnet within reasonable range.  The ideal location is on-axis, where the field is parallel to the face of the magnet and the two field components are perfectly matched.  There are other ideal locations that can be found where two of the components will have equal magnitude.  To allow for non ideal locations, TMAG5170 also integrates gain adjustments for a programmable channel.  This allows the user to correct mismatch in amplitudes and reduce overall error.  

TMAG5170 also will convert the result to an angle output, reducing the effort for the microcontroller, whereas a 1D linear device like DRV5055 would require an ADC to convert the signal and then the microcontroller would need to calculate the angle. Operating over SPI allows the device to communicate digitally and reduce impact of electrical noise on signal integrity.

Thanks,

Scott

Dajon

Here is a short writeup on Steering column sensors that should help answer your questions. In general there is a lot more mechanical flexibility and lesser number of sensors needed with 3D Hall-effect sensors compared to 1D linear Hall-effect sensors. So if you are using more than one sensor, you should consider looking at the more dynamic 3D Hall-effect sensors.

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In a steering column, in addition to the electric power steering systems (EPS), there is also the steering column control module (SCCM) or indicator control module through which the driver controls multiple functions like wiper control, turn signal control, cruise control, headlight control etc. For these mechanical and electrical interface, multiple levers are present around the steering column that move in all directions as well as have push button feature at the end of the levers.

In automotive systems, the SCCM uses the steering angle sensor from the EPS as an input and also has dedicated Hall-effect sensors specific to the SCCM functions. It all depends on the architecture being adopted. The steering angle sensors (SAS) of the EPS provides the information about the rate of turn and angle position of the steering wheel as input to the SCCM and the vehicle stability control (ESC or VSC) system. This is an important part of the vehicle safety in emergency as well as standard operation of the vehicle.

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For the steering angle and column sensors, a 3D Hall-effect sensor is a good choice as it allows for both angle and position sensing with one sensor. Due to its ability to sense all three dimensions, a linear 3D Hall-effect sensor  allows for on-axis as well as off-axis detection of  the position of the magnet inside the steering column which rotates with the turn of the steering wheel.  All this while the steering angle sensor module stays fixed on a module mounted around the steering column rod. The angle sensor output is used by the SCCM to automatically disable turn signals when the steering is rotated in the direction of the turn and returns back to the normal position. In newer vehicles the same angle output is also used to direct the headlight in the direction of the turn. 

In addition to the angle sensor, either Hall-effect switches and or 3D Hall-effect sensors are used to determine the position of the steering column control levers. Multiple switches can be replaced with a single 3D sensor to detect the movement of the control levers in all directions as well as push button feature of the lever for integrating multiple functions on a single control lever.

Getting started with TI's Hall-effect sensors

Automotive steering column designers can use TI's TMAG5170-Q1 linear 3D Hall-effect sensor with integrated CORDIC angle calculation and built in fault diagnostics for systems with ASIL-B safety level requirements. This specific Hall-effect sensor IC supports output of the angle and position information through the serial peripheral interface (SPI).  The DRV5023-Q1 is a very popular vertical Hall-effect switch that can be used for the control levers in addition to the 3D sensor. In systems where there is vertical space constraints or there is a need for horizontal or in-plane sensing, the new TMAG5123-Q1 is another option for a high precision Hall-effect switch.

Additional Resources

• For more information on TI’s Hall-effect sensors, check out our Magnetic Sensors page

• Application note on angle measurement with multi-Axis linear Hall-Effect Sensors

• TI Precision lab (TIPL) video training series on Magnetic Sensors