Infineon Rolls Out Magnetic Position Sensor Using TMR Technology
By measuring position with magnetics, the new position sensor frees up system real estate for designers.
In a bid to shrink the size of position sensors, Infineon has launched the Xensiv TLI5590-A6W magnetic position sensor for small, high-precision consumer and industrial applications. These sensors can replace optical encoders and Hall sensors for position measurements and purportedly offer extremely high linearity compared to previous generations of magnetic sensors.
The Xensiv TLI5590 provides high-precision position measurements in an extremely small package. Image used courtesy of Infineon
As moving devices continue to shrink, position sensors ensure proper performance in different operating conditions. As such, Infineon designed its newest chip to strike a balance between precision and size to continue miniaturization. This article takes a closer look at the science behind the new sensor and gives readers a sense of how it may be used for robust, high-precision length measurements.
Length Measurement With Spintronics
At the heart of the new Xensiv sensor is a spintronics-based device that has recently seen use in both position sensors and magnetic memory: the magnetic tunnel junction (MTJ). The MTJ consists of two ferromagnetic layers separated by an insulator through which electrons can tunnel, creating current. If, however, the magnetization of one layer is changed, the effective resistance can be changed as well, creating the tunnel magnetoresistance (TMR) effect.
The TMR effect changes the resistance of an MTJ using an external field. This allows the Infineon sensor and a magnet to create an analog position measurement. Image used courtesy of Tsinghua Science and Technology
While resistance itself cannot be directly measured by an ADC, an onboard Wheatstone bridge effectively converts the changing TMR resistance to a measurable voltage. If an external magnet is used to change the magnetization, the position of the magnet can be determined using two collaborative TMR sensors.
Compared to other sensor types, such as Hall or optical sensors, the TMR sensor can improve linearity and noise performance, while still maintaining a high degree of precision.
A Super Small Measurement Device
In addition to its high precision, the new Xensiv sensor is remarkably small. The TLI5590 (datasheet linked) is currently available in a six-bin BGA package spanning only 1.27 mm × 0.93 mm.
The TLI5590 is powered from a 1–5.5 V supply and can measure a magnetic field parallel to the chip’s plane between -5 and 5 mT. The device requires a multipole external magnet with a pitch of ~500 µm to perform measurements, with a maximum angle error ranging from ±2.5–4.1°. The device is qualified for industrial and consumer measurements according to the JEDEC standard JESD47K.
As the multipole magnet moves, the relative output voltage at each bridge changes, allowing designers to sense position using magnetics. Image used courtesy of Infineon
The output of the two magnetic bridges can be digitized directly by a microcontroller with a few additional components. As a result, designers can considerably reduce the overall size of a position measurement system. Infineon has also reported an accuracy higher than 10 µm (assuming a proper magnetic encoder is used), making it potentially useful for small devices such as automatic camera lenses.
Magnets Enabling Miniaturization
As a low-field sensor, the TLI5590 is claimed to offer linear and angular incremental position detection in high-volume sensor systems.
Infineon reports that the device's combination of high sensitivity, high signal-to-noise ratio, low power consumption, and low jitter may enable a new wave of low-cost magnetic designs.