Position sensor has interference field compensation

September 30, 2020 //By Christoph Hammerschmidt
Position sensor has interference field compensation
TDK's HAL 3970 is a 3D position sensor for automotive applications such as steering angle detection and linear position measurement in transmissions and couplings. Special features of the component include active interference field compensation and an SPC interface.

The new sensor enables highly accurate angle measurement from 0 to 360 degrees and linear position detection. Short PWM code frames (SPC) are used to transmit the calculated position information. SPC is an extension of the standard SENT protocol according to SAE J2716, whereby the trigger pulse of an external ECU starts the data transmission. Supported are point-to-point connections as well as the single-wire bus mode with up to four sensors. Clock pulse, frame format, trigger mode, slow channel format, rolling counter and other parameters can be easily configured.

The sensors of the HAL 39xy family are based on TDK's patented 3D HAL pixel cell technology. The HAL 3970 uses a special arrangement of Hall plates for highly accurate measurement of vertical and horizontal magnetic field components. Due to this special arrangement, the sensor detects angles up to 360 degrees and compensates for the effects of external magnetic interference fields. Only a simple two-pole magnet is required to determine an angle of rotation. For measurement at the end of a rotating shaft, the magnet should ideally be placed above the sensitive sensor area. The sensor also supports interference field-safe measurements next to the shaft axis.

The on-chip signal processing of the HAL 3970 calculates an angle from the individual magnetic field components and outputs it as a digital value. A DSP and a microcontroller are integrated in the sensor. The DSP is responsible for fast signal processing, while the microcontroller handles the interface configuration and ensures functional safety. Important characteristic values such as gain, offset and reference position can be adapted to the magnetic circuit by programming the non-volatile memory. HAL 3970 is defined as SEooC (Safety Element out of Context) ASIL B ready, according to ISO 26262. HAL 3970 is available in SOIC8-SMD package.

More information: https://www.micronas.tdk.com/en/products/direct-angle-sensors


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