Sensor package saves cost, meets ASIL D

October 27, 2014 // By Christoph Hammerschmidt
Electric power steering systems typically need two sensors to measure steering torque. A dual-sensor package developed by Infineon combines both sensors in one package which not only shrinks the space requirement but also the cost. The device supports ASIL (Automotive Safety Level) D, the highest level required for safety-critical applications.

The chipmaker now has introduced two product families that already use the new package - a linear Hall sensor and a steering angle sensor. An innovative stack mounting technology enables them to combine two sensors within standard and space-saving PG-TDSO packages only about 1mm thin. Instead of the usual 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). Other application fields include throttle control, pedal position and brushless DC motor control in areas like 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. Thus, the two sensors work independently which increases reliability of the system. The SMD packages have 8 pins or 16 pins.

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.

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 requiring larger packages and stronger magnets. Using larger, more expensive magnets also results in design effort needed for exact magnetic field