Typically, it needs two sensor chips today for reliable and precise sensing of the steering torque in an electric power steering system. Thanks to a dual-sensor package of Infineon Technologies, it will be only one sensor chip in future. Infineon has introduced two device families of linear Hall sensors and angle sensors that already use the new dual-sensor package. It supports ASIL D systems and reduces physical space requirements and system cost; for example in steering applications requiring high availability as used in autonomous driving. The dual-sensor package was developed at the Infineon site in Regensburg, Germany.
By using stack mounting technology, the devices of the linear Hall sensor and angle sensor families combine two independent sensors within standard and space-saving PG-TDSO packages only about 1mm thin. Instead of the common approach of side-by-side sensor placement, Infineon stacks the two sensors with a patented flip-chip technique. This saves precious space and cost in safety critical applications, such as electric power steering (EPS), throttle control, pedal position and brushless DC motor control in such areas as EPS motors, transmission and clutch actuators.
The dual-sensor package integrates two linear Hall sensors or two angle sensors. Both sensors have separate power supply and separate signal outputs. They are electrically independent due to galvanic isolation. This means that the two sensors work independently which increases reliability of the system. The SMD packages have 8 pins or 16 pins. Using these packages, Infineon also offers single sensor versions.
Sensor redundancy is of particular interest for new generations of EPS systems with increased ISO 26262 requirements and for other safety critical applications that rely on Hall effect torque sensors and GMR/AMR (Giant Magneto Resistance / Anisotropic Magneto Resistance)angle detection. The dual-sensor package supports ASIL D systems; Infineon provides ISO 26262 documents and safety expertise to assist its customers – automotive system suppliers – in the design of ISO compliant systems.
“Automotive safety requirements according to ISO 26262 demand sensor redundancy for safety critical applications like electric power steering,” said Ralf Bornefeld, vice president and general manager of the Sense and Control business at Infineon Technologies. “Underlining our leadership in the automotive sector with the broadest magnetic sensor portfolio in the market, Infineon addresses the need for sensor redundancy by intelligently integrating two sensors in one package. With two sensors in one small package, our customers can reduce their system costs and design very compact ASIL D systems.”
Footprint of dual-sensor package is identical to a single-sensor
With the flip-chip mounting technique of the dual-sensor package, both sensing elements are placed in the same lateral position and detect a single uniform magnetic field, which can be compared directly by the associated system microcontroller. The flip-chip mounting technique enables very small package dimensions and a PCB layout with reduced space. In comparison, conventional side-by-side sensor methods detect different magnetic fields. This means the magnetic field must be stronger than the one with the dual-sensor package leading to larger packages, the need for stronger more expensive magnets, and field variations due to the distance between the two sensing elements. Using larger, more expensive magnets also results in design effort needed for exact magnetic field trimming. With the new Infineon sensor families, engineers can make use of smaller, less expensive magnets and they can skip the effort on magnetic field trimming.
The dimensions of the new PG-TDSO-8 package for linear Hall sensors are identical to the footprint of single sensor devices, at just 4.0mm x 5.0mm x 1.2mm (height inclusive stand-off). Infineon also offers angle sensors (both with GMR and AMR technology) in a PG-TDSO-16 package. All sensors in dual-sensor packages are specified for a temperature range of -40 °C to 125 °C and automotive qualified.
Availability of dual-sensor package technology devices
Engineering samples of linear Hall sensors TLE4997A8D and TLE4998x8D in the PG-TDSO-8 package are already available. Volume production is planned to start end of year 2014.
Engineering samples of angle sensors TLE5012BD and TLE5309D in the PG-TDSO-16 package are also available. The TLE5012BD integrates two sensors using iGMR-based technology, while the TLE5309D integrates one sensor using iAMR-based technology and one sensor using iGMR-based technology. Volume production for angle sensor TLE5012BD is scheduled to start end of 2014 while volume production of TLE5309D is planned to start mid-2015. Infineon also offers the linear Hall sensors and angle sensors as single-sensor solutions.
