December 5, 2020

Space- and power-saving 3D magnetic sensor for industrial and consumer applications

10 min read
The miniaturization trend is also shaping the world of sensors. Smartphone applications, industrial joysticks, medical...

The miniaturization trend is also shaping the world of sensors. Smartphone applications, industrial joysticks, medical devices, gaming consoles and all sorts of other consumer electronic devices all rely on a growing number of sensors – which often need to be packed into a very tight space. Sensor miniaturization enables more compact designs or greater functional integration on the same footprint. Magnetic sensors increase system robustness, reduce sensitivity to environmental factors like dirt and moisture, and increase the lifespan and reliability of the final product. To capitalize on these benefits, Infineon developed the Xensiv TLI493D-W2BW 3D magnetic sensor. Bringing powerful features to an extremely small wafer-level package and opening up completely new design options, this sensor was launched in August 2020.

With the TLx493D 3D magnetic sensor family, Infineon offers an accurate three-dimensional sensor technology with extremely low power consumption in a highly compact package. The family includes versions for consumer (TLV), industrial (TLI) and automotive (TLE) applications. Using magnetic field detection along the X, Y and Z axes, these sensors reliably measure three-dimensional, linear and rotating 360° movements. Typical use cases include automobile gear shift sticks, gear shift selectors, joysticks, domestic appliance pushbuttons, multi-function control knobs, meters, robotic controls and other applications where accurate and compact angle/position measurements and low power consumption are key success factors. The most recent addition to the family is the Xensiv™ TLI493D-W2BW. Designed for both industrial and consumer applications, it comprises a latest-generation 3D Hall sensor in miniature wafer-level packaging (WLB or wafer level ball grid) with power-saving and wake-up functions as well as an I2C interface.

Whereas conventional linear Hall sensors, optical solutions and angle sensors only detect magnetic field components at a vertical angle to the chip surface, 3D magnetic sensors like the TLI493D-W2BW (figure 1) can also determine the X, Y and Z coordinates of the magnetic field. By detecting the magnetic field components of all three axes, the sensor builds a holistic three-dimensional image of the magnetic field, which means fewer components are required. Every movement by the magnet changes at least one magnetic field component, which is detected by the 3D sensor. This three-dimensional sensing capability is achieved by integrating vertical and horizontal Hall plates on the sensor chip. The vertical Hall plates detect horizontal movements of field components along the X and Y axes. The horizontal Hall plate detects vertical movements of the field component along the Z axis.

Figure 1: The TLI493D-W2BW 3D magnetic sensor combines accurate position measurement with an extremely compact and energy-efficient design.

Due to their exceptionally small form factor and low power consumption, TLx493D sensors are also suitable for applications which previously avoided magnetic sensors. Hence they are an ideal replacement for potentiometers and optical solutions, for instance. Contactless position sensing and the high temperature stability of the magnetic thresholds pave the way for smaller, more accurate and more robust system concepts. A two-wire I²C standard interface supports fast communication, bus mode and bidirectional communication between the sensor and microcontroller. Infineon’s 3D magnetic sensors are ROHS-compliant and JEDEC JESD47-qualified to ensure that customer systems fulfill the highest quality standards and comply with various environmental regulations.

Compared with resistance-based and optical solutions, magnetic sensors offer numerous advantages including high accuracy (over the entire lifetime and over temperature fluctuations), robustness, a high level of reliability in harsh environments with dusty or moist conditions, and redundancy (multiple 3D sensors) if required. In addition, magnetic sensors are easier to handle and offer greater design flexibility for a more haptic user experience.

Architecture

The sensor architecture (figure 2) of the Xensiv™ TLI493D-W2BW consists of three main functional units: the power mode control system, the sensing unit and the I2C interface.

 

Figure 2: Block diagram of the TLI493D-W2BW with power mode control, sensing unit and I2C interface.

The power mode control system contains a low-power (LP) oscillator, a biasing function, an accurate restart function, undervoltage detector and a fast oscillator (F-OSC). The sensing unit contains the vertical and horizontal Hall plates, a temperature sensor, multiplexers and AD converters. It measures the magnetic field along the X, Y and Z axes and can also take temperature measurements for efficient compensation. The I2C interface contains the register files and I/O pads.

The microcontroller can access the communication unit via the I2C interface to read out register values. The values for the three axes and the temperature are stored in separate registers. The interface fulfills the I2C fast mode specification (400 kbit/s). Data rates of 1 Mbit/s and above can be achieved thanks to the special electrical set-up. The use of a communication bus system reduces the number of cables required and enables a microcontroller-based control mechanism (bus master). With 3D magnetic field detection, the sensor offers 12-bit data resolution for every direction of measurement. This enables a high data resolution of 0.098 mT per bit (LSB), meaning that even the very smallest movements can be measured. Linear magnetic field measurements (B) of Bx, By and Bz are possible for the large linear field range of +/-160 mT. This means that magnets can also be measured over longer travel paths. In addition, wide operability ranges enable a simple, robust and flexible magnetic layout design. The sensor targeted at industrial applications supports a voltage range from 2.8 to 3.5 V and a temperature range from -40°C to +125°C.

Functional highlights

The TLI493D-W2B6 uses the latest 3D Hall generation from Infineon and has a few extra features relative to the previous generation. For instance, the new sensor comes with an integrated wake-up function and even better drift capabilities (sensitivity and matching). The customer can select from variants with four pre-defined standard addresses. A larger measuring range and higher resolution contribute to ease of use over a wider range of applications. Magnetic flux densities with +/-160 mT can now be detected at a programmable resolution of 65 µT (typ.). XY angle measurement is also supported. Diagnostic functions check the digital and analog switching circuits and the Hall element of the sensor. The current consumption in power-down mode is specified at only 7 nA (typ.). The supply current is 3.4 mA. The sensor can be triggered by an external microcontroller via the I2C protocol and it has a dedicated interrupt pin. The update rate goes up to 5.7 kHz (8.4 kHz for XY), while the resolution in the low-power modes can be adjusted in eight steps between 0.05 and 770 Hz.

The Xensiv™ TLI493D-W2BW is available in an extremely small WLB-5 package (figure 3). Compared with the previous TSOP-6 packages (2.9 mm x 2.8 mm x 1.1 mm), the wafer-level packaging (1.13 mm x 0.93 mm x 0.59 mm) further reduces the space required on the PCB by around 87 percent and the thickness of the component by approximately 46 percent. The low assembly height is particularly advantageous in extremely space-critical applications such as micromotors or gaming consoles.

 

Figure 3: The miniature wafer-level packaging reduces PCB space requirements for innovative compact designs.

The new Xensiv™ TLI493D-W2BW with its extremely small form factor allows designs with double-sided printed circuit boards or the sensor to be positioned between two PCBs (buried sensor, figure 4). This makes it possible to make even better use of the available PCB space. For example, further components can be placed above the sensor. In addition, the I2C interface reduces the number of microcontroller pins required for a smaller MCU.

Figure 4: The new TLI493D-W2BW with its extremely small form factor allows designs with double-sided printed circuit boards or the sensor to be positioned between two PCBs (buried sensor).

Power mode control and wake-up mode

The power mode system distributes power across the IC. It has a power-on reset function and a special low-power (LP) oscillator as the clock source. When the system has been started, the functional unit activates the biasing function and provides an accurate reset detector and a fast oscillator (FOC). After that, the sensor goes into low-power mode and can be configured via the I2C interface. Once the configuration has been completed, the measuring cycle can be performed with the following steps: activation of internal biasing, checking of restart function and provision of fast oscillator. After that comes Hall biasing and – as standard – a sequential measurement of the three Hall element channels (including the temperature). The final step is a return to configuration mode.

The sensor can also be set to automatic measuring mode whereby it only activates (wakes up) the system if the magnetic field exceeds pre-configured thresholds. This is another way to reduce the amount of power consumed. The wake-up function (figure 5) has an upper and a lower comparison threshold for each of the three magnetic channels (X, Y and Z). Each component of the applied magnetic field is compared with both of these threshold values. If one of the results is above or below these thresholds, an interrupt pulse (/INT) is generated and the wake-up function is triggered. The sensor then sends a corresponding signal to the microcontroller. As long as all components in the field stay within the defined range, no interrupt signal will be sent.

Figure 5: Wake-up mode: How does it work?

The sensor is equipped with different power modes which the user can select according to the requirements of their particular application: power-down mode (lowest possible power consumption), low-power mode (cyclic measurements and AD conversions with different update rates), fast mode full range (continuous measurements and AD conversions), fast mode short range with low update frequency, and master-controlled mode (measurements triggered by microcontroller via I2C interface). The power consumption can be reduced by up to 50% if the temperature and Bz are not measured. By default, temperature measurement is active.

Evaluation kit and simulation tool

Infineon provides a range of design-in kits for simple and low-cost evaluation of its 3D sensors. These help developers at the early stage of the design process by supporting the important magnetic set-up process. This enables designers to verify that the sensor and the magnet fulfill their performance requirements.

To simplify design-in, Infineon offers useful resources such as Sensor 2Go kits (figure 6). These are low-cost evaluation boards with a 3D magnetic sensor and an Arm® Cortex®-M0 CPU. The kits have all the required components and functions for efficient design-in including a debugger.

 

Figure 6: Design support for 3D magnetic sensors like the TLI493D-W2BW is available with tools such as sensor 2Go evaluation kits – shown here with the linear slider as magnet holder.

As well as the 3D magnetic sensor, the board has an XMC1000 microcontroller connected to the sensor and an XMC4200 microcontroller for debugging and USB communication. A micro-USB connector is provided for power and communication with the GUI. The board also features power status and debugging LED indicators plus user-customizable LEDs, voltage regulators, and reverse current and ESD protection diodes. The external wiring (oscilloscope, external microcontroller, etc.) can be implemented with a pin header. The scope of delivery includes a stand-alone magnet which can be manually positioned. Infineon also offers magnet holders (add-ons) which can be attached to the evaluation board to give an idea of how a magnetic design would look (figure 7). These add-ons benefit customers by demonstrating ready-to-run solutions for particular use cases.

 

Figure 7: Magnet holders (add-ons) can be attached to the evaluation board to demonstrate a variety of magnetic designs.

The add-on library is regularly updated. Demos available to date include a joystick, a rotation knob and a linear slider. The linear slider can be used to adjust distance traveled and air gap in order to detect linear movements.

These have now been expanded with specific drill trigger and HMI (human machine interface) direction indicator add-ons. The latter brings nine possible settings to a car’s indicator switch. Infineon also makes 3D print files of these add-ons available on its website to further assist customers in their development process. The customer can simply produce these adapters themselves straight away on a 3D printer, test them, and integrate them into their mechanical workflow: http://www.infineon.com/sensors2go

In addition, Infineon offers an online simulation tool (https://design.infineon.com/3dsim/) to trial typical 3D magnetic sensor applications. These include angle measurement, linear position measurement and joystick applications. The tool offers pre-defined or customer-specific magnets for each of the three applications – and Infineon can also provide a magnet recommendation list. For each sensor position, the tool automatically calculates the three magnetic field components along the X, Y and Z axes. This calculation is based on the sensor configuration that was pre-defined by the user. The assembly tolerances for the sensor and the magnet are also considered in this calculation.

Complementing these affordable and easy-to-use design-in kits (Sensor 2GO) for the 3D position, current and speed sensors, Infineon further supports the design process with extensive documentation (application notes, user manuals, FAQs, 3D print files, datasheets) and Arduino shields (https://github.com/Infineon/3D-Magnetic-Sensor-2GO)

For more information on Infineon’s 3D magnetic sensors, go to: http://www.infineon.com/3dmagnetic

Conclusion

In addition to three-dimensional magnetic field measurement, the new Xensiv™ TLI493D-W2BW from Infineon’s family of 3D magnetic sensors offers a high level of accuracy, an extremely compact footprint and very low power consumption. The miniature wafer-level packaging and integrated wake-up function for even lower power consumption open up interesting new design possibilities. Variable update frequencies and power modes (configurable during operation) make this flexible sensor suitable for a variety of use cases. Interference caused by small stray fields is negligible due to the high magnetic flux density.

Contactless magnetic field detection, high temperature stability and practically zero wear-and-tear pave the way for new development opportunities such as novel joysticks for industrial applications (human-machine interface). New 3D sensors also enable cost- and energy-efficient controls such as user-friendly rotary knobs / pushbuttons in electrical or domestic appliances, joysticks and gaming consoles, as well as accurate and robust position measurement in robotics.

Infineon supports evaluation and design-in of its magnetic sensors with evaluation kits, add-ons and other tools (simulation). Add-ons give customers a simple and practical way to demo a concrete solution for their specific application.

The post Space- and power-saving 3D magnetic sensor for industrial and consumer applications appeared first on EETimes.

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