Hall-effect sensor solution based on Melexis

The Hall Effect sensor changes its output voltage in response to a magnetic field. Hall effect devices are used as proximity sensors and used for positioning, speed and current detection. Hall effect sensors are a long-term solution because no mechanical parts will wear out over time.

The Hall Effect sensor changes its output voltage in response to a magnetic field. Hall effect devices are used as proximity sensors and used for positioning, speed and current detection. Hall effect sensors are a long-term solution because no mechanical parts will wear out over time.

Melexis announced the launch of the MLX91377 linear Hall sensor IC for ASIL, suitable for safety-critical automotive systems, such as electric power steering (EPAS). MLX91377 was developed as a security element out of context (SEooC), conforms to the ISO 26262 standard, and has passed the AEC Q-100 level 0 certification.

Hall effect sensor

The Hall effect is a measurable voltage that is affected by a magnetic field when the current flowing through it passes through a conductor (or semiconductor). Under these conditions, due to the balance of Lorentz force (electromagnetic force) and electric power, a transverse voltage is generated perpendicular to the applied current.

The design of any Hall-effect detection device requires a magnetic system that can respond to the physical parameters detected through the Electronic input interface. The Hall effect sensor detects the magnetic field and generates a standard analog or digital signal according to the requirements of the electronic system.

Since this allows them to work without contact, Hall sensors have a wide range of applications: they are used as proximity, positioning and speed sensors, for example.

In its simplest form, a Hall sensor is used as an analog sensor, which returns a voltage. Therefore, in a known magnetic field, the distance to the Hall plate can be measured. It is also common to find Hall sensors combined with circuits that enable the device to act in a digital way (on/off), thereby acting as a switch. Another typical application of Hall sensors is to measure the speed of axles and wheels, for example in speedometers, internal combustion engine ignition systems or anti-lock braking systems.

Automotive applications face various operating conditions ranging from extremely cold (-40°C) to extremely hot (160°C). In addition, they are also subject to high vibration and potential contamination from dust, dust, liquids, etc. Even under these conditions, they require years of trouble-free operation. Hall sensors need to perform well even in such a wide range.

Melexis solutions

MLX91377 combines high linearity and excellent thermal stability (including low offset and sensitivity drift) at an ambient operating temperature of up to 160°C, and supports accurate and reliable torque sensing in the EPAS system, which enables it to perform in conventional and Realize safety control in automatic driving.

MLX91377 meets various automotive and industrial non-contact position sensing use cases, including steering torque sensors, acceleration, brake or clutch pedal sensors, absolute linear position sensors, float level sensors, non-contact potentiometers, small angle position sensors and Small stroke position sensor.

MLX91377 has improved performance across the board, enabling critical safety applications with strict requirements, such as automotive torque sensing. There is currently no development board available, but MLX91377 is supported by the standard Melexis programming tool PTC-04. Said Nick Czarnecki, global marketing manager for Melexis position and speed sensors.

Hall-effect sensor solution based on Melexis
Figure 1: Block diagram of MLX91377

Programmable measurement range and multi-point calibration increase the flexibility of designers, and multiple output protocols allow a single integrated circuit to be used for multiple applications, thereby reducing re-certification efforts and costs. The short PWM code (SPC) protocol allows measurement and transmission of the measured value after the trigger pulse is detected. In this way, up to four MLX91377 sensors up to 2 kHz can be synchronized, so that magnetic parameters can be measured at the same time with a deterministic waiting time to ensure high accuracy (Figure 1).

“Depending on the output type, the MLX91377 can be triggered by the protocol or internally. MLX91377 provides two methods. When using the SPC protocol, the MLX91377 will wait until the control microcontroller receives the trigger pulse,” Nick Czarnecki said.

He continued: “When a pulse is detected, the sensor quickly acquires magnetic data, digitizes it and compensates for offset and sensitivity errors, linearizes it according to the programmable lookup table, and then according to the SENT format. It works in analog output mode. MLX91377 will automatically acquire data, perform the same compensation as in SPC mode, and then output the value through analog proportional voltage for system microcontroller to read. Both interfaces are widely used in automobiles, and SPC is updated. Usually the first choice for multi-IC configurations. The triggerable feature of SPC allows all sensors to acquire the magnetic field at the same time, thereby minimizing the time delay between cross-IC measurements.

Hall-effect sensor solution based on Melexis
Figure 2: 1.5μs tick time mode and SPC timing diagram in H.2 format

In SPC mode, regardless of the configured mode, once the trigger pulse is received, the MLX91377 starts data collection. It will send the acquired data in the same SENT frame. This function is suitable for any tick time greater than or equal to 1.5μs (Figures 2 and 3).

Hall-effect sensor solution based on Melexis
Figure 3: SPC standard master-slave configuration

MLX91377 supports ASIL-C functional safety level in digital mode (SENT or SPC), supports ASIL-B in analog mode, provides high-level diagnosis at the die level, and can detect internal faults and put itself in a safe state, thereby Prevent unnecessary vehicle behavior.

The next challenge will increasingly see that the critical temperature of the operating environment is getting higher and higher. Similarly, with the increase in the electrification of vehicles, the immunity to the leakage field will become wider and wider, and the requirements for functional safety will also become higher and higher.

The Links:   C084XAN01.0 7MBR50SB120H-70 TIMMA LCD

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