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Magnetic position sensors offer DAEC on chip

25 Jun 2014  | Peter Clarke

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AMS AG, formerly known as Austriamicrosystems, has announced a lineup of magnetic position sensors for angle detection that perform dynamic angle error compensation (DAEC) due to propagation delay on the sensor chip. The "47 series" is based on Hall effect principles with four sensors on the die so that the direction and speed of rotation can be married. The family comprises the AS5047D, the AS5147 and the AS5247.

The ability to output a compensated reading, provides a high accuracy down to ±0.17° at 14,500 revolutions per minute and allows users to dispense with error compensation that is conventionally done in software in a separate DSP chip or in a host processor.

The AS5047D is geared for industrial applications including robots and encoder modules, the AS5147 is an AEC-Q100 qualified part for automotive applications such as electronic power steering and pumps and the dual die AS5247, also AEC-Q100 qualified, is intended for automotive applications that require redundancy for functional safety compliance.

AS5047D

Traditional magnetic rotary position sensor ICs suffer from a propagation delay of about 100-200ms as they convert raw measurements of magnetic field strength at their embedded magnetic elements into digital angle measurements. During this delay, a spinning rotor's angular displacement changes, so that its actual position when the digital output leaves the sensor differs from its measured position.

On the 47 series a DAEC algorithm performs error compensation internally and responds automatically to changes in the speed of rotation. The 47 series sensors provide angle measurements accurate ±0.08 degrees at 7,000rpm, to ±0.14 degrees at 12,000rpm and ±0.17 degrees at 14,500rpm.

All three devices provide absolute position measurements as a digital PWM output, and UVW outputs for use in field-oriented commutation schemes. They also provide an incremental ABI output equivalent to the output of an optical encoder. This means an AS5047D IC can replace an optical encoder without requiring the user to change the software interface in the host system's MCU or DSP.

The 47 series devices offer high 14bit resolution (to 0.022°) in their digital SPI output, and maximum resolution of 2,000 steps per revolution in decimal mode and 2,048 steps per revolution in binary ABI mode.

The 47 series benefits from a proven differential sensing technique, which offers immunity to stray magnetic fields and enables the devices to be used in electrically noisy environments without any requirement for shielding.

The AS5047D and AS5147 are sampling in a 14-pin TSOP and priced at under $5 in 1,000-piece quantities. The AS5247 come in a 40-pin 7 x 7mm package. General availability of all three starts at the end of July.




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