Single-chip integrated circuit optimizes the design of adaptive headlight system

High-intensity discharge (Xenon) vehicle headlights are increasingly becoming the technology of choice for vehicle manufacturers around the world. In order to maximize the high-quality illumination provided by Xenon lamps while reducing the danger of excessive Xenon light intensity due to improper direction, Adaptive Front Lighting Systems (AFS) are becoming increasingly important.

These systems can slightly adjust the headlight beam in the vertical direction to compensate for changes in the vehicle's inclination relative to the road. At the same time, they can also rotate the headlights in response to changes in the vehicle's steering. This beam provides the best and safest illumination of the road ahead, significantly improving the driver's visibility when turning.

1. Automatic leveling - reducing strong light

The automatic headlight leveling system works by keeping the lights level with the road even when the vehicle is tilted (see the figure below). The vehicle may tilt when it is stationary, for example, when passengers are boarding, luggage is loaded, or even when the fuel tank is filled. Similarly, when the vehicle is moving, it may tilt due to braking or acceleration. In both cases, the headlights must remain level with the road. The automatic headlight leveling system adjusts the angle of each lamp based on a series of data from sensors, especially the suspension compression data from the front and rear axles.

2. Improve safety performance by rotating headlights

The vehicle's data network includes real-time sensor data on steering angle and wheel speed. Based on this information, the adaptive headlight system equipped with the headlights can adapt the light distribution to the vehicle's steering angle so that oncoming turns and junctions - and specifically the driver's gaze point - are optimally illuminated (see figure below). This significant increase in light reduces driver stress and fatigue and improves visibility of obstacles that fixed-beam headlights can't even reach. Many studies have shown that swiveling-beam headlights improve illumination of the driver's gaze point by 300% when the vehicle is turning.

3. Stepper Motor Control

Each vehicle's headlights are moved using stepper motors, one for vertical movement and one for horizontal movement (see the figure below). The motors react to data from many sensors around the vehicle. Information is communicated via the vehicle's data network. The LIN bus is a practical choice for headlight control, while the CAN bus collects and distributes sensor data throughout the vehicle. Stepper motors are a good choice for headlight adjustment applications because they are low-cost, rugged, and provide a lot of torque in a small package.

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There are two options for where to place the driver IC chips that control the stepper motors. The first is called direct drive. In this approach, the driver chip is mounted on the main microcontroller PCB (see top image below). This board is located far away from the headlight assembly and the associated stepper motors, either in a central electronic control unit (ECU) attached to the vehicle bulkhead (thermal wall) or in the "comfortable" environment of the vehicle's passenger compartment. The main disadvantages of this approach are the excessive amount of wiring required and the high level of EMC emissions.

The second approach is mechatronics. In this approach, the driver chip is mounted together with the motor (see bottom of the figure above). The mechatronics approach to adaptive headlight systems where the chip can be mounted directly in the motor has become more feasible due to the use of highly integrated single-chip products such as the AMIS-30621 and AIMS-30623 stepper motor controller integrated circuits manufactured by AMI Semiconductor. This approach is very beneficial because the interface connection between the central microcontroller and the mechatronics module only requires a low-EMC bus. The mechatronics approach has significant benefits due to its modular design and easy maintenance of the headlight assembly.

4. Separation of Hardware and Software

The application of stepper motor drivers requires the design of both hardware and software. This can become very complex, especially when multiple axes need to be controlled simultaneously, as in an adaptive headlight system. Before the advent of stepper motor controller integrated circuits, the approach was to invest in a microcontroller and develop dedicated software, or use a conversion chip (see the figure below, left and middle pictures). The main problem with software-based solutions is that they are expensive to develop and there are inherent difficulties in verifying the correct operation of multiple axes under all conditions.

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So-called converter ICs provide the interface between the microcontroller and the driver chip, adding some extra hardware to the overall solution but also leading to more unmanageable complexity and more software requirements (see the image below, right). The downside of using a converter chip is that it makes the PCB design more complicated and loses some of the advantages of modularity.

5. Single chip Method

The integrated stepper motor controller reduces the complexity of adaptive headlight systems requiring multiple axes compared to other approaches and provides a straightforward solution that vehicle manufacturers need to support modular and integrated vehicle designs.

AMI Semiconductor offers four mixed-signal devices that combine bus connectivity, positioning, electronic control and motor drive in a single package with a footprint of 7mm*7mm. These devices are small and high-performance, and they can still ensure modular design of motion control software and robust motor operation when installed directly inside the stepper motor.

The two models (AMIS-30621 and AMIS-30623) feature a LIN bus interface. Compared to systems that place the driver remotely, this approach saves wiring costs and has better electromagnetic compatibility, an advantage that is key to solving problems when encountering difficulties in automotive applications. The remaining two improved models (AMIS-30622 and AMIS-30624) have an I2C serial interface and can be used as a peripheral device adjacent to a microcontroller on a single printed circuit board.

6. Sensorless Stop Detection

Most automatic headlight systems make an initial position adjustment when the lights are turned on. This mechanical method basically adjusts the lights to the lowest possible point within a specified time. One problem with this procedure is that the stepper motors create noise and increase wear due to hitting the stop points. Another solution is to use sensorless stop detection, which features the application of AMIS-30623 and AMIS-30624 components. These components are quiet in operation and low in wear, but they can also accurately calibrate the position and can use semi-closed loop operation when approaching the electromechanical stop points without the need for external sensors.

VII. Conclusion

The use of a single-chip stepper motor controller integrated circuit can greatly simplify the design of adaptive steering headlight systems and provide excellent technical performance in conditions that are usually difficult to operate. The integrated design greatly improves the overall reliability of the headlight and means that only a few capacitors are required as external circuit components. Likewise, time to market, design and overall system costs will be positively affected.

Both the mechatronic and modular approaches are supported by single-chip stepper motor controller integrated circuits and are favored by vehicle manufacturers as the rapid growth of vehicle electronics makes the electronic system architecture too complex and expensive.