Next-generation LED Drivers for Exterior Lighting in the SDV

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The automotive industry is facing major disruptions. Increasing electrification and the trend toward software-defined vehicles (SDV) may be the most obvious ones  – accompanied by advances and changes in all areas of automotive development.

These developments have significant implications for automotive exterior lighting: One major transformation will be the shift from distributed to zonal control, which several car OEMs have introduced and many more are expected to follow. Additionally, new design trends with animations but also ADB (Adaptive Driving Beam), high-definition pixel lights and communication displays, present designers with challenges. And lastly, engineers have to consider the growing importance of driving safety and cybersecurity that comes together with increasing data communication in the SDV’s architecture.

In the future, the trend to change the battery voltage from 12 V to 48 V will also have an impact on lighting electronics. The reason lies in the new requirements of the car manufacturers and the relevant ISO standards, which are underway.

Architectural shift to Zonal

While all automotive manufacturers are considering to introduce zonal architecture, only around 5% of cars are equipped with this technology today. But by 2030, it is expected to be in almost every third car, and by 2040 in as many as 70% of all cars.

Today’s lighting ECUs or lighting driver modules – widely used for headlamps – are dedicated to delivering the power coming from the battery into the lamp modules. They control many of the lamp’s functions such as brightness, beam position, safety functions, and thermal management. As of today, they typically integrate an MCU running the control and safety application software and communicating through the car network with other ECUs such as the domain controller.

Thus, all essential functions are implemented in the software of each lighting ECU, including control, calibration, safety, derating – to name a few. For each different lamp variant, a new software version needs to be released and run through testing and certification processes, often only for one specific hardware version used maybe within just one country or region.

For cost efficiency reasons, the lighting ECU hardware is designed to serve many lamp variants from one car manufacturer. As this ECU is mainly defined by the amount of power to be delivered and the number of output channels, it is specified to fit within a certain car segment of the market. For example, many low-end car models from one OEM might use the same HW version of that ECU. But the software running on this ECU needs to follow the individual lamp specification and design of each car model, adding up on complexity.

With the introduction of the zonal architecture in the car, a part of the “smart functions” is moving out of the lighting ECU and into the zonal controller’s application software.

The impact on the lighting ECUs hardware functions could be challenging. But this is desired since there are still some critical functions that cannot be shifted to the zonal controller and need to stay inside the ECU, mainly for safety and reaction time reasons but also for cost efficiency.

The data traffic between the zonal controller and several lighting ECUs is increasing significantly, so that typical communication interfaces must be upgraded or replaced by faster ones. The division of responsibilities between the zonal controller software and the ECU must be very well defined, with proven fallback scenarios, for example, in case of communication delays or even total data disconnect (limp home).

MCU-less and software-less lighting ECUs

The lighting ECU can be simplified by introducing more intelligent power components such as LED drivers and motor drivers. These integrate more control and safety functions, autonomous state engines, and faster communication interfaces on top of the already increased level of integration in power delivery.

The target is to even remove the MCU out of the lighting ECU. Such an “MCU-less” scenario leads to the maximum demand for communication to and from the ECU. At the same time, the level of autonomous behavior is also the highest.

But often, a trade-off between an MCU-less design and a “traditional” approach (with an MCU) could be a smart choice. This is especially true for mid- or high-end variants, where both budget and space allow it and complexity and data traffic would be too high. In this case, a communication bridge inside the ECU helps to bring both worlds together, without the need for flexibility in the software and without model variations. This is typically called a “software-less” lighting ECU architecture, since a communication interface bridge running a lightweight firmware replaces the traditional MCU.

Smart Driver ICs for MCU-less ECUs

The typical components of the lighting ECU, such as boost and buck LED drivers, stepper motor drivers, bypass switching, and linear LED drivers, need to integrate the increased demand on smart features previously served by the MCU: smart control features, faster connectivity and communication interfaces, extensive functional safety features and enhanced state engines in case of failures, autonomous derating for both internal and external use cases and more rich positioning and motion profiles with features for leveling and swiveling.

In addition, increased memory for data storage, e.g., for binning or other manufacturer information, flexibility on the communication protocol or dialects, but also low-level connections like GPIOs are necessary to control the system functions.

ROHM’s driver portfolio for lighting ECUs supports extensive smart and communication features for MCU- and software-less designs. The products also offer possibilities for higher integration and efficiency for the lighting module’s power delivery. In this way, they contribute to the ever-growing requirements for space and cost savings.

The increased demand for animations, higher number of pixels, and even communication graphics (displays/projections) drive the data traffic to a much higher level. Automotive Ethernet could become the future interface between the zonal controller and the lighting ECUs, connecting adequately to all areas of the car.

Outlook to 48V and modular lights

In addition to the trends described, in the future there will also be the change in the voltage of the power supply system. While 12 V systems are predominantly used today, 48 V systems based on the voltages used in electric vehicles will increasingly be used in the future. Some OEMs are already including 48 V systems in their planning, but unlike zonal architecture, this is by no means universal and is not being given the same priority by all. ROHM is therefore focusing on solutions that can be used in both 12 V and 48 V systems.

In addition, some OEMs are investigating the so-called modularization of the lighting system, where each lighting module, like a high beam or DRL (Daytime running lamp), integrates its own power driver instead of a common lighting ECU for the complete lamp. The goal is more flexibility, easier repairs, and eventually lower overall cost.

Conclusion

Automotive OEMs and Tier 1s are facing major changes with the shift from distributed control to zonal control architecture, the transition to MCU-less or software-less architecture, and the increasing communication and safety requirements that come with it. ROHM is addressing all these challenges with its new driver ICs for exterior lighting. With well-thought-out solutions that tackle the challenges facing the industry, ROHM helps developers bring their designs to market quickly and reliably.