Automotive lighting continues to develop rapidly. Although LED light sources can improve efficiency and have a unique vehicle style, original equipment manufacturers (OEMs) are now implementing novel and useful lighting use cases. In this technical article, I’d like to focus on several semiconductor technologies that are influencing the roadmap of headlight, taillight and interior lighting systems.
Adaptive headlight system
Adaptive headlight system and adaptive high beam headlight system adjust the shape of low beam and high beam respectively. Although adaptive headlights can be used in European cars, American car manufacturers cannot use these advanced lights. However, that may soon change. The adaptive system uses high-power LED as light source, which requires high-power LED driver to adjust the current and achieve the required brightness. Switched LED drivers must be used to achieve high efficiency and a two-stage power handling topology for thermal management.
The first stage is a boost regulator. It manages a wide range of vehicle input voltages and creates a stable intermediate power rail. The second stage is buck current regulator, which can be realized by low output capacitance suitable for dynamic LED load. However, since LED drivers are used as switching regulators, you will have to deal with the challenge of electromagnetic compatibility (EMC).
LED driver and matrix manager features and options
Considering the development speed of headlamp system, the flexibility of design is very important. In the adaptive system, you can use the new tps92682-q1 dual channel, dual phase led controller as the constant voltage boost regulator of the first stage of the headlamp. If you have static headlamps on your roadmap, you can configure the device as a constant current buck boost / boost / single ended primary inductor converter (SEPIC) led driver. Tps92682-q1 also has programmable spread spectrum modulation function, which can help to easily meet EMC requirements.
For the second stage of Buck current regulator, another device tps92520-q1 provides high power density in a compact solution size, which is realized by a single chip, Dual Synchronous Buck constant current LED Driver with a switching frequency up to 2.2MHz and serial peripheral interface. In addition to the high integration and power density provided by tps92520-q1, its control architecture also provides true average current regulation, as well as dynamic and matrix load compatibility.
Although tps92682-q1 and tps92520-q1 can be used as the driving force of the electronic control unit (ECU) of the headlamp and can be found in any headlamp system, the matrix Manager IC is responsible for adjusting the beam shape of the headlamp. The matrix manager is located on the pixel board of the headlamp, which can precisely control the intensity of each pixel to generate different beam patterns and illuminate the whole field of vision, while avoiding the glare from the face.
Figure 1: adaptive headlight system
Since LED pixel board is usually connected to ECU through wiring harness, it needs to cope with the challenges of reliable communication and reduced wiring harness size. Tps9266x-q1 provides a robust and lightweight communication interface and a complete set of diagnostic procedures, which can directly detect and report pixel level led faults to ECU.
Reference design of headlamp ECU
Learn how our two new LED drivers achieve a complete 120 W matrix compatible ECU for adaptive headlamps.
DLP ® Technical features and options
The headlamp based on Ti DLP technology can not only adjust the beam shape of the headlamp with high resolution; They also enable symbol projection to assist the driver. The symbol can communicate with the driver and other people on the road. For example, the use of headlights to draw lane markings for planned vehicle paths on the road can help drivers navigate in dangerous driving conditions and also communicate with other vehicles to be driven. The dlp5531-q1 chipset is suitable for automotive industry standards and has been optimized for headlamp applications and today’s roads. View DLP automatic headlight reference design.
Motor functions and options
Another way to change the light beam is to adjust the headlight level, in which the light beam can illuminate the road regardless of the inclination of the road or whether the driver accelerates or decelerates. When the headlamp is pointed to the road, the field of vision can be improved especially when driving at night, so as to improve the driving safety. Bipolar stepper motor is usually used to control the headlamp level. Drv8899-q1 stepper motor driver not only has the power level of driving motor, but also has the function of stall detection without additional sensors.
With the continuous expansion of lighting control module based on communication technology, TI’s can transceiver products (such as tcan1044-q1), Lin transceiver products (such as tlin1029-q1), and system based chips (such as tcan4550-q1 and tlin14415-q1) are good choices for automotive lighting applications.
Dynamic tail light
In terms of tail light signal functions such as stop lights and direction indicators, LED light sources are becoming more and more versatile and can now even cover dynamic and / or personalized lighting messages.
The automotive two-stage (SEPIC + linear) static LED driver module reference design for taillights shows the two-stage LED driver. The first voltage regulator is realized by lm5155-q1 in SEPIC topology. This buck boost topology allows the lamp to operate at low battery voltage and down regulate at high battery voltage to optimize the second stage LED driver from the perspective of thermal management.
Ti’s new 12 channel high side LED driver tps929120-q1 is specifically developed for dynamic lighting applications. The device uses flexwire (the unique interface of Texas Instruments) to achieve separate pixel control. Flexwire is a universal asynchronous receiver transmitter (UART) interface, with automatic baud rate detection function, so the high led counting system can be independently dimming. The complete diagnosis and fail safe mode can ensure the reliability of the complete LED lamp.
Digital interface led driver module reference design
Use our reference design on the digital interface led driver module to quickly launch your taillight design.
Tps929120-q1 includes 12 bit pulse width modulation (PWM) dimming and provides off board support for taillights that may span the entire length of the vehicle, as shown in Figure 1. As shown in the digital interface led driver module reference design, tps929120-q1 can be connected with can or Lin communication transceiver to improve communication stability.
Other taillights trends
Taillights are realizing a new signal mode that combines style and personalization. An example is a slip turn in which the direction indicator LEDs turn on in sequence rather than all at once, making it look as if it is sliding the direction indicator. Another trend is to use tail lights to display welcome messages for drivers, and even message alarms for drivers behind the car.
Personalized interior lighting
The lighting in the cockpit is also changing. One of the changes is the use of a large number of LEDs to display personal messages (e.g. welcome messages) or to adapt the beam to a specific position (e.g. on the front passenger seat when moving).
Tlc6c5724-q1 is a 24 channel red, green and blue LED driver, which can control each channel independently, which is very important for partition applications. The LED driver perfectly combines with the front-end buck converter (such as lmr33630-q1 or lmr36015), which can be used for personalized interior lighting, such as partition dome lamp or RGB lighting. Lmr33630-q1 is a 36V input voltage / 3A output current device, while lmr36015 is a 60V input voltage / 1.5A output current device with a maximum junction temperature of 150 ° C. The front-end step-down regulator improves the thermal performance of the solution, such as the EMC tested reference design of automotive pixel ceiling lamp for interior lighting.
Brighter, customizable small lamp
The original intention of the ground projection is to light up near the vehicle to help the driver drive in. The next generation of small lights will use DLP technology to achieve dynamic ground projection. This technology can not only change the projection position dynamically, but also change the projection content dynamically. This function can convey information to drivers before they enter the car, warn people around the car or provide automobile manufacturers with brand promotion opportunities. Cars with small static lights that project static symbols, such as logos, are now available.
Transparent window display
With the continuous growth of carpooling tide, it is necessary to develop a system to display sharing related messages to customers. In addition, the trend of autopilot requires vehicle to communicate with other vehicles and pedestrians.
One space where such messages can be displayed is the window. DLP technology can project information on the window when the car is parking, and keep the window view clear when the car is driving. This DLP projector combines with special screen technology and can also display advertisements on the windows. This is an attractive prospect for auto OEMs.
There are many types of screen technology that can achieve transparent window display, and for many of them, DLP projectors are naturally suitable for illuminating the screen. One technology is a light-emitting phosphor film embedded in the window excited by 405 nm light inside the DLP projector. Ti’s dlp3034-q1 and dlp5534-q1 both support 405 nm based lighting sources.
The lighting system of the whole vehicle is realizing new and exciting functions. Ti’s semiconductor products make these functions and reference designs easier, providing you with a better design starting point and shorter time to market.