Dual sensors support safety-critical applications

27th October 2014
Posted By : Barney Scott
Dual sensors support safety-critical applications

 

Reliable and precise sensing of the Electric Power Steering (EPS) torque in an electric power steering system has previously always required two sensors to function. Thanks to Infineon's dual-sensor package innovation, only one sensor chip is likely to be required in future.

Two device families of linear Hall sensors and angle sensors have already been introduced which use the dual-sensor package. The package supports ASIL D systems and reduces physical space requirements and system cost.

The devices of the linear Hall and angle sensor families combine two independent sensors within standard and space-saving PG-TDSO packages approximately 1mm thin, by replacing the common approach of side-by-side sensor placement with an innovative stack mounting technology,

Safety critical applications, such as EPS, throttle control, pedal position and brushless DC motor control in areas such as EPS motors, transmission and clutch actuators, will experience space-saving and cost benefits from using the patented flip-chip technique.

Using flip-chip mounting, very small package dimensions and a more compact PCB layout can be achieved, as both sensing elements are placed in the same lateral position and detect a single uniform magnetic field. The field can be compared directly by the associated system microcontroller.

Conventional side-by-side sensor methods detect different magnetic fields, which must be stronger than the field detectable with the dual-sensor package. Side-by-side sensors require larger packages, stronger, more expensive magnets and variations in the magnetic field. Using the dual-sensor package, engineers can utilise smaller, cheaper magnets and reduce the effort required for magnetic field trimming.

The package, with 8 or 16 pins, integrates two linear Hall or two angle sensors, both of which have separate power supplies and signal outputs, and are electrically independent due to galvanic isolation. Reliability of the system is increased as both sensors work independently of each other.

For new generations of EPS systems with increased ISO 26262 requirements, as well as for other safety critical applications that rely on Hall effect torque sensors and GMR/AMR (Giant Magneto Resistance/Anisotropic Magneto Resistance) angle detection, sensor redundancy is of particular importance. Automotive system suppliers are offered assistance in the design of ISO compliant systems, as ISO 26262 documents and safety expertise are provided by Infineon.

Identical to the footprint of single sensor devices, the PG-TDSO-8 package for linear Hall sensors measures just 4.0x5.0x1.2mm (height inclusive stand-off). Angle sensors with GMR and AMR technology are also offered, in a PG-TDSO-16 package. All automotive qualified sensors in dual-sensor packages are suitable for a temperature range from -40 to +125°C.

Samples of linear Hall sensors TLE4997A8D and TLE4998x8D in the PG-TDSO-8 package are available, and volume production is planned to commence at the end of 2014. 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 and one using iGMR-based technology. Volume production for angle sensor TLE5012BD is scheduled to start at the end of 2014, whilst volume production of TLE5309D is planned to start mid-2015.


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