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Automotive Hall-effect rotary-position sensor uses novel flux-concentrator technology
By Paul Rako, Technical Editor -- EDN, 10/18/2007
Melexis uses its expertise in advanced process technology as well as a novel approach to magnetic concentration in the design of the new MLX90316 Hall-effect rotary-position sensor. The eight-pin-SOIC device provides 12-bit resolution and 10-bit accuracy over its temperature range. Because reliability is critical in the device’s targeted applications—throttle-pedal positioning, for example—Melexis has versions of the part that integrate two fully redundant sensors into one TSSOP-16 SMD package.
Melexis uses the novel Triaxis flux concentrator in the magnetic path; the device converts B-fields in the plane of the die into orthogonal fields that penetrate the die. Melexis applies this concentrator as a back-end deposition to the normal CMOS-process flow. After the flux concentrator presents the B-field to the integrated Hall-effect sensor, a differential-analog-signal chain, which includes chopper amplifiers to minimize noise and improve accuracy, takes possession of the analog signal. An ADC digitizes the Hall signals, which then go to an on-die-integrated 16-bit RISC microprocessor. This processor includes filters that users can implement as hysteretic, FIR (finite-impulse-response), and IIR (infinite-impulse-response) devices. The Hall-effect sensor’s output has four ranges, allowing manufacturers to do a quick two-point sensor calibration or a more time-consuming three- or five-point calibration for better linearity.
The chip provides PWM- and serial-protocol outputs, as well as a DAC to output an analog signal. In addition, a switch output changes level when the sensor reaches a programmable threshold. Self-diagnostics include memory checks, overvoltage and undervoltage detection, and ground-integrity checks. The processor includes a watchdog timer. In addition, the chip self-checks the ADC, the DAC, and the on-board regulator.
The chip suits automotive applications requiring high voltage or able to withstand high temperatures in engine-torque, steering-wheel, fuel-level, ride-height, and pedal-position sensors. You can also use the chip in applications requiring rotary or 3-D positions, such as joysticks for entertainment control and seat position. Although the chip’s designers had automotive applications in mind, it suits use in industrial and medical applications requiring reliability and temperature range of –40 to +150°C for both the SOIC-8-packaged MLX90316LDC and TSSOP-16-packaged MLX90316LGO. Prices are approximately $2.40 and $4.56 (10,000), respectively.
