Hall-Effect sensors with PWM and SENT interfaces

Micronas announced two new members of its varioHAL family of fully-integrated Hall-effect sensors with digital interfaces. The HAL 2830 and HAL 2850 both include a microcontroller, a temperature sensor, advanced on-chip compensation, and a digital output format. The HAL 2850 features a PWM (Pulse-Width Modulated) interface, while the HAL 2830 has a SENT interface used particularly for low-cost automotive sensors in high-noise environments.

Electrical noise - static - is severe in automotive applications, especially under the hood. An accurate sensor is of little use if its output does not reach the microcontroller accurately. Since electrical noise primarily affects the amplitude of a signal, one way to insure accurate results is to use the width of the signal to represent the value being measured. The HAL 2850 uses pulse-width modulation; this pulse is sent to the system microcontroller, and its width is measured with a counter-timer module, a common feature of virtually all microcontroller 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 2000 per second. This 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 microcontroller. 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.

Both the HAL 2850 and HAL 2830 offer 12-bit accuracy. Internally, both devices are fully digital and can be programmed with a 12-bit customer serial number, The devices have industry-standard open-drain outputs, but offer slew-rate control on these to reduce EMI (Electro-Magnetic Interference) problems. In addition, the HAL 2830 offers a temperature measurement capability.

Along with the HAL 2830 and HAL 2850, Micronas offers an application kit containing a programmer board, LabVIEW(TM) 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.