Knowing the distance between the magnet and the sensor as well as the magnet properties, the angle error
can be estimated using the
. However, since this application does not require a
fast sampling rate, the CORDIC algorithm with a high sample averaging applied will give accurate enough
information about the dial's position.
2.2.5 CORDIC Algorithm
The built in CORDIC algorithm uses two magnetic axes to determine the angle data. The linear magnetic axis
data can also be used to calculate the angle using an external algorithm as well. For using the internal CORDIC
algorithm, the desired magnetic axis need to be selected using the ANGLE_EN bits in the SENSOR_CONFIG_2
register in the device. For this design, the X and Y axis are used to determine the magnet angle so the bits are
set to 0x1. In addition to this, it is important to set the magnetic sensing range based on the expected magnetic
field strength. Once configured, the magnet angle can be obtained from the CORDIC algorithm by simply
reading the ANGLE_RESULT_MSB and ANGLE_RESULT_LSB registers. Lastly, averaging is applied to the
sampling of the device by changing the CONV_AVG register setting. This allows for a better SNR performance
from the device and gives more accurate angle information from the CORDIC output.
2.3 Highlighted Products
2.3.1 LDC3114-Q1
The LDC3114-Q1 is an inductive sensing device that enables touch button design for human machine interface
(HMI) on a wide variety of materials by measuring small deflections of conductive targets using a coil that can be
implemented on a small printed circuit board (PCB) located behind the panel. This technology can be used for
precise linear position sensing of metal targets for automotive, consumer and industrial applications by allowing
access to the raw data representing the inductance value. Inductive sensing solution is insensitive to humidity or
non-conductive contaminants such as oil and dirt.
The button mode of LDC3114-Q1 is able to automatically correct for any deformation in the conductive targets.
The LDC3114-Q1 offers well-matched channels, which allow for differential and radiometric measurements
which enable compensation of environmental and aging conditions such as temperature and mechanical drift.
The LDC3114-Q1 includes an ultra-low power mode intended for power on/off buttons or position sensors in
battery powered applications.
2.3.2 TMAG5273
The TMAG5273 is a low-power linear 3D Hall-effect sensor designed for a wide range of industrial and personal
electronics applications. This device integrates three independent Hall-effect sensors in the X, Y, and Z axes.
A precision analog signal chain along with an integrated 12-bit ADC digitizes the measured analog magnetic
field values. The I 2C interface, while supporting multiple operating VCC ranges, ensures seamless data
communication with low-voltage microcontrollers. The device has an integrated temperature sensor available
for multiple system functions, such as thermal budget check or temperature compensation calculation for a given
magnetic field.
The TMAG5273 can be configured through the I2C interface to enable any combination of magnetic axes and
temperature measurements. Additionally, the device can be configured to various power options (including wake-
up and sleep mode) allowing designers to optimize system power consumption based on their system-level
needs. Multiple sensor conversion schemes and I2C read frames help optimize throughput and accuracy. A
dedicated INT pin can act as a system interrupt during low power wake-up and sleep mode, and can also be
used by a microcontroller to trigger a new sensor conversion.
An integrated angle calculation engine (CORDIC) provides full 360° angular position information for both on-
axis and off-axis angle measurement topologies. The angle calculation is performed using two user-selected
magnetic axes. The device features magnetic gain and offset correction to mitigate the impact of system
mechanical error sources
System Overview
8
Inductive Touch and Magnetic Dial Contactless User Interface Reference
Design
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