Rotary position sensor suits safety-critical automotive use

Providing reliable performance in automotive applications, an ultra-high speed magnetic rotary position sensor has been introduced by ams. The AS5147P's accurate absolute and incremental measurement outputs at speeds up to 28,000rpm make it suited for use in safety-critical applications such as electric power steering, brake and accelerator pedals, pumps, double-clutch transmissions, starter motors, alternators and windscreen wiper motors.

The combination of high measurement accuracy at high rotation speeds, high reliability, low system cost and support for the ISO26262 functional safety standard make it appeal to automotive system designers.

The AS5147P draws on patented DAEC (Dynamic Angle Error Correction) technology to deliver accurate position measurements even at extremely high rotation speeds. The DAEC compensation scheme reduces the propagation delay inherent in the sensor’s signal chain to almost zero. As a result, the AS5147P’s angle error is a negligible 0.02° at 1,700rpm, 0.17° at 14,500rpm and 0.34° at 28,000rpm. The DAEC function also enables the device to refresh its measurement output every 1.9µs.

High reliability and low system cost in automotive applications are assured by the AS5147P’s intrinsic immunity to stray magnetic fields. Strong stray magnetic fields are present in vehicles, particularly those with a partially or wholly electric drivetrain, which contain powerful electric motors and high current-carrying conductors. These stray magnetic fields are much stronger than that of the small target magnet with which a magnetic position sensor is paired.

The unique differential sensing principle of the magnetic position sensors from ams makes them immune by design to stray magnetism. This means that automotive system designers can avoid the need to incorporate bulky and expensive magnetic shielding into their products, reducing their size, weight and cost when compared to designs based on competing magnetic position sensor ICs. The high sensitivity of the AS5147P also enables the use of a small (6mm diameter), low-cost target magnet.

The AS5147P provides both absolute and incremental angle measurements of a continuously rotating shaft, with a zero-position setting. A standard four-wire serial peripheral interface allows a host MCU to read 14-bit absolute angle position data and to programme non-volatile settings without a dedicated programmer.

Incremental movements are indicated by a set of ABI signals with a maximum resolution of 4,096 steps/1,024 pulses per revolution. The resolution of the ABI signal is programmable to 4,096 steps/1,024 pulses per revolution, 2,048 steps/512 pulses per revolution or 1,024 steps/256 pulses per revolution. BLDC motors may be controlled through a standard UVW commutation interface with a programmable number of pole pairs from one to seven. The absolute angle position is also provided as a PWM-encoded output signal.

Heinz Oyrer, Senior Marketing Manager, ams, commented: "Offering a combination of high accuracy, compact size and low system cost, magnetic position sensors are widely regarded as the best solution for rotary position sensing in vehicles. Now with the AS5147P, ams has made a magnetic position sensor which fits seamlessly into OEMs’ ISO26262 compliance programmes and which also eliminates any concerns over the effect of stray magnetic fields."

The AS5147P is available now in production volumes in a TSSOP-14 package. Unit pricing is $5.31 in 1,000 unit quantities.

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