Inductive position sensor accelerates automotive system electrification

Believed to be the first inductive position sensor for high-speed motors available as a standard product, the AS5715 sensor IC delivers cost, size and weight savings compared to the resolvers in common use in vehicles today, says ams.

The sensor is for used in high-speed, automotive and industrial electric motors for rotor position sensing. The IC is based on an ASIL-C implementation and the redundant implementation supports ASIL-D to comply to the ISO 26262 functional safety standard.

Commercialisation of the inductive position sensor is intended to advance the electrification of automotive systems such as power steering and traction systems in electric and hybrid electric vehicles (EVs and HEVs). The AS5715 inductive sensor is configurable, and can be used in on-axis (end-of-shaft) and off-axis (through shaft or side-of-shaft) topologies, and with many types of multi-pole-pair motor.

Chris Feige, executive vice president for automotive solutions at ams, said: “Motors built with the AS5715 will be smaller and lighter, and deliver a smoother, more powerful output. This, coupled with cost savings are . . . reasons for automotive manufacturers to replace expensive, cumbersome resolvers with the AS5715 inductive sensor”.

The automotive electric motor market is changing, with the permanent magnet synchronous motor (PMSM) supplanting the brushless DC motor in many high-speed applications. At the same time, government regulations worldwide are tightening the requirements on the car industry to cut average fuel consumption. By replacing legacy electro-mechanical and hydraulic automotive systems with efficient, electronically-controlled motors, car manufacturers can reach their fuel consumption targets more quickly.

The highly accurate, low-latency position measurements produced by the AS5715 underpin the operation of electric motor-control systems, enabling high-speed motors to maximise torque, limit torque ripple, and achieve high efficiency. A position sensor system based on an AS5715 IC and its associated coil printed on a simple, low-cost PCB can achieve accuracy up to ±0.3 degrees at rotation speeds up to 100,000rpm in various motor types including four-pole-pair PMSMs.

Developers who have worked previously with resolvers will find they are familiar with the mode of operation of the AS5715, asserts ams. It provides two pairs of differential analogue outputs, as sine waves and co-sine waves. These may be resolved to an angle measurement by applying an arctan function in the host controller.

ams provides documentation and applications guidance to design the Tx and Rx coils in the static sensor PCB and the rotating target assembly affixed to the rotor.
The AS5715 also supports automotive manufacturers’ programmes for compliance with ISO 26262. A fully redundant measurement system can be implemented by mounting two AS5715 ICs on the sensor board.

The AS5715 is available for sampling now. An evaluation kit for the AS5715 inductive position sensor is available on request from ams.

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