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Hall-effect sensors transfer data in harsh automotive setups

Posted: 08 May 2008 ?? ?Print Version ?Bookmark and Share

Keywords:Hall-effect sensors? varioHAL? digital interfaces?

HAL 2850, HAL 2830

Micronas has rolled two new members of its varioHAL family of Hall-effect sensors with digital interfaces enabling robust and reliable data transfer in harsh automotive environments. The HAL 2830 and HAL 2850 both include an MCU, a temperature sensor, advanced on-chip compensation and a digital output format. The HAL 2850 features a pulse-width modulated (PWM) interface, while the HAL 2830 has a SENT interface used particularly for low-cost automotive sensors in high-noise environments.

Fighting electrical noise
The HAL 2850 uses PWM; this pulse is sent to the system MCU, and its width is measured with a counter-timer module, a common feature of virtually all MCU designs. Variations in amplitude due to noise are ignored.

The HAL 2850 can be programmed to send pulses as slow as 30 per second, or as fast as 2,000 per second. This wide range allows the system designer to tailor it to the system needs. A slower update rate may suffice for slowly-changing variables such as temperature, and reduces the overall load on the MCU. A faster rate may be required for fast-changing variables such as pressure.

The HAL 2830 takes this a step further. It uses the SAE J2716 SENT standard to transmit sensor information, again using the time between pulse edges to represent the sensor value. SENT improves on traditional PWM techniques by providing a reference calibration pulse at the beginning of the signal, and a checksum at the end to detect errors. The HAL 2830 also includes a sensor-status signal as well as the measured value. SENT can replace lower-resolution methods using 10bit ADCs and PWM techniques and provides a simpler, low-cost alternative to digital busses such as CAN or LIN. SENT is used particularly for low-cost automotive sensors in high-noise environments.

Both the HAL 2850 and HAL 2830 offer 12bit accuracy. The increased accuracy helps designers manage power train applications more precisely, thus reducing pollution and improving fuel economy. Internally, both devices are fully digital and can be programmed with a 12bit-customer serial number. The devices have industry-standard open-drain outputs, but offer slew-rate control on these to reduce EMI problems. In addition, the HAL 2830 offers a temperature measurement capability.

"The HAL 2830 and HAL 2850 combine the advantages of Hall-effect sensors with proven digital error-correction and compensation techniques, and now we have added high-reliability signal transmission methods," says Peter Zimmermann, market manager automotive at Micronas. "Putting it all on one chip creates a low-cost, high-accuracy solution that will help meet the next generation needs for power train applications such as engine management and steering torque."

Other features
The HAL 2830 and HAL 2850 sensors are produced in a submicron CMOS technology already well-proven in automotive applications. Like all members of the varioHAL family, the HAL 2830 and the HAL 2850 feature a temperature-compensated Hall-plate with spinning-current offset compensation, an ADC for the Hall-plate, and an ADC for the temperature sensor. The temperature compensation uses an advanced second-order algorithm, and can be calibrated by the user in-system for greater overall accuracy. All processing is done digitally via a RISC processor and an EEPROM with redundancy and a lock function for the calibration data. The devices have protection circuits on all pins. For high-volume applications, customers can develop their own firmware variant according to the desired behavior of the device.

Along with the HAL 2830 and HAL 2850, Micronas offers an easy-to-use application kit containing a programmer board, LabVIEW programming software and the necessary source code. Key application variables such as sample rate, magnetic field range, sensitivity, offset and the temperature coefficients of sensitivity and offset can be adjusted by programming the non-volatile memory. Programming is done via BiPhase-M telegrams. The sensor is programmed through its output pin; no additional programming pin is needed.

The HAL 2830 and HAL 2850 are offered in a TO-92UT package rated for use from -40C to 170C. Pricing and availability vary with model.

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