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Automotive lighting is rapidly evolving driven by the combination of electric vehicles, ADAS and desire for modern styling. The automotive industry continues its shift towards electrification resulting in noticeable changes to an automobile’s exterior lighting. In the past, large single-function lights dominated the front, back, or sides of a vehicle. However, newer, slim designs that wrap around the car have taken their place. Car manufacturers are using lighting as a signature styling feature and are incorporating animations to symbolize a brand identity. These new designs are not only aesthetically pleasing but also serve a practical purpose.
Animated tail lamps are not new, as they were first introduced in 1960’s muscle cars such as the 1965 Chevrolet Impala SS. It featured a unique taillight design known as “Impala Super Sport Sequential Taillights,” which included a sequential lighting pattern that animated the turn signal indicators. Since then, advancements in automotive LEDs, MCUs, and the rise of electric vehicles has increased the popularity of animated tail lamps. Car designers now have flexibility in designing animated lights that display information or add unique personalized signature stylings. For example, some cars now feature LED lighting that makes it easier for other drivers or pedestrians to anticipate the car’s movements or provide a ‘welcome’ lighting sequence to the vehicle’s owner.
While animated tail lamps are not legally required, when installed on a vehicle they must meet region specific lighting safety standards. In the US, these regulations are established under Federal Motor Vehicle Safety Standard (FMVSS) No. 108. It outlines the technical specifications for lighting devices, such as the color, intensity, positioning, and alignment of lights on vehicles sold for use on US public roads. In Europe and parts of Asia, similar standards fall under the United Nations Economic Commission for Europe (UNECE) Regulation No. 48. The aim for all lighting regulations is to improve visibility, promote consistent, reliable signaling, and improve overall safety of vehicles on public roads.
Despite minor regional differences, the commonality is all passenger vehicles must have at least two red taillights symmetrically positioned on either side of its longitudinal centerline that’s visible from a certain distance in normal daylight conditions (e.g., 100 meters UN ECE R48). Both FMVSS108 and UN ECE R48 were recently updated for LED lights that set minimum luminous intensity, color and PWM derived flicker rates. All three of these new requirements will have implications for LED based, animated tail lamps.
In order to create LED lamps that are both functional and aesthetically pleasing, engineers and designers face new challenges in controlling a multitude of LED pixel dots instead of just a few LED strings. As car designs become more streamlined and aerodynamic, the shape and placement of lights become more critical. Car lamps will have to fit seamlessly into the overall design of the car while still providing adequate visibility, safety, reliability, energy efficiency and conformance to government regulations.
Animated exterior lights help improve road safety by providing additional information to other drivers. As these lights become more sophisticated, they can display more safety information using complex patterns and animations. This will require a shift from controlling blocks of LED strings or incandescent bulbs to driving individual LED pixels. To accomplish this, a significant amount of engineering and design innovation is required. Special drivers are needed to form a matrix or cluster of individually controlled LEDs that span the entire rear of the car. Only LED drivers with a digital interface can control the large number of LEDs required for animated lighting.
Figure 1 shows the evolution of lighting control architecture from traditional to newer animated pixel lighting.
A vehicle’s lighting system is managed by a body control module (BCM) that contains electronics and a microcontroller (MCU). The BCM manages various electrical and electronic systems in the vehicle’s body, including lighting, windows, mirrors, seats, and doors.
In the past, lighting animation was not a requirement, so the BCM could easily enable FET or relay switches to control LED strings or incandescent bulbs using the MCU’s general-purpose input/output (GPIO) pins. Today, the BCM’s MCU needs to control a variety of lamps having different LED arrangements and animation patterns. With the increasing demand for animated lighting functions, the BCM now interacts with a lighting dedicated electronic control module (ECU) to send commands to multiple LED drivers that control groups of individual LEDs.
Design Challenges for Animation Lighting
Automotive engineers who undertake the design of animated lighting systems face some daunting challenges such as controlling heat, meeting functional safety goals and keeping the cost minimized. Although LEDs possess numerous advantages over incandescent bulbs, there are also challenges in driving them to fit automotive requirements. By carefully choosing the appropriate LED type and its driver, the challenges associated with regulatory compliance, optics, housing, and electrical aspects of the design can be simplified. The selected LED driver should have the capability for fine-tuning individual LED brightness with fast and accurate communication between the ECU and the LED lighting system.
Example Split RCL Design
The wide variation of rear combination lamp (RCL) designs gives vehicles a distinctive and unique look. The transition from incandescent bulbs to LED rear lamps has opened a wide range of design possibilities, such as animated turn signals, animated welcome lighting, and more. Achieving a split lamp design lighting effects requires multiple LED drivers to control a wide range of LEDs with different lumens per watt and different colors from white, amber, red, and super red. These lighting components can be spread out over the vehicle and interconnected using wiring harnesses.
The rear combination lamp is shown in Figure 2; it is a split design where half the lamp is on the car body while the other half is located on the trunk. Accomplishing a seamless animation effect requires communication over noisy wiring harnesses which can affect animation reliability. To solve these issues, a controller-area network (CAN) bus is required to ensure fast, reliable communication. The CAN bus links the BCM to the ECU and the ECU to the LED drivers.
Lumissil Microsystems provides a diverse range of LED drivers designed to meet the demands of animated lamp designs while addressing the challenges mentioned earlier.
The IS32LT3138A LED driver from Lumissil is designed to establish dependable off-board communication between the microcontroller (MCU) control board and the driver (See figure 3). It offers a high-speed 1MHz UART interface that is compatible with the CANFD physical layer. The IS32LT3138A accomplishes reliable long-distance communication by using an industry-standard UART-to-CAN physical layer at the transmit side and another at the receiving end of a wire harness. Each driver has 18 high voltage (16V) constant current channels to facilitate the use of LED strings. By using a single resistor, all OUTx channels can be configured to sink up to 100mA.
Lumissil offers many cost-effective, unique solutions for automotive LED lighting in the categories of high brightness, matrix and animation. One of our new LED drivers for automotive animation is the IS32FL3749. It is a matrix LED driver with a fast 33MHz serial-shift daisy-chain bus that can inter-connect multiple IS32FL3749 devices. Each driver has 24 high voltage (16V) constant current channels. This high voltage capability facilitates the substitution of each pixel with a string of LEDs whose forward voltage can be up to 16V (Figure 4). By using a single resistor, all row channels can be configured to sink up to 60mA. This driver also includes four column controls, allowing it to drive a 24 (row) × 4 (column) LED array, for an array size of 96 LEDs. Each LED within the array can also be mapped into RED, GREEN, or BLUE groups to achieve an RGB group control reducing data programming traffic.
Fault Diagnosis & Functional Safety
Since the reliability of automotive rear lamps has a direct impact on road safety, LED driver IC needs to monitor their vehicle’s rear lamps. Even a minor lamp failure can potentially lead to an accident. Fortunately, LEDs have a life expectancy longer than a vehicle’s operating life. However, they are still susceptible to random failures. Both the IS32LT3138A and IS31FL3749 incorporate LED fault detection and reporting capabilities to meet functional safety goals. Failure events are logged into registers that are accessible to the MCU through the bus interface.
Conclusion and Summary
Exterior automotive lighting serves a greater purpose than simply ensuring optimal vehicle visibility. It has evolved to become a major driving force behind innovative designs for automotive rear lamps. A new generation of lighting designs using animated LEDs has emerged and replaced traditional incandescent bulbs and LED strings. Today’s vehicles require innovative lighting technologies that serve both functionality and brand identity. This next level of automotive lighting effects can only be achieved through the independent control of numerous LEDs.
Advanced LED drivers like the IS32LT3138A and IS32FL3749 enable lighting designers to manage and display automotive lighting effects, while enhancing safety and enriching the overall user experience. Lumissil Microsystems offers other animation-focused LED drivers, such as the IS32LT3146, a standalone sequential lighting driver, and the IS32FL3248, a 48-channel serial-shift driver. These and other LED drivers play a crucial role in enabling contemporary lighting technology while simultaneously improving traffic safety for everyone.
To learn more please visit us at www.lumissil.com
About Lumissil Microsystems
Lumissil Microsystems is a division of ISSI specializing in analog/mixed-signal products for automotive, communications, industrial, and consumer markets. Lumissil’s primary products are LED drivers for low to mid-power RGB color mixing and high-power lighting applications. Other products include audio amplifiers, sensors, high-speed wired communications, optical networking, multi-media microprocessors, and application-specific microcontrollers. ISSI and Lumissil Microsystems are headquartered in Silicon Valley, California with worldwide offices in Taiwan, Japan, and Singapore, mainland China, Europe, Hong Kong, India, and Korea.