LED string concept facilitates ambient lighting designs

November 10, 2016 // By Christoph Hammerschmidt
An open alliance of enterprises (plus one university) has developed a concept for experience-oriented ambient lighting in future car generations. The concept is based on digitally addressable and controllable LEDs that can change color and make binning – the painstaking process of selecting LEDs with exactly the same brightness and color - a thing of the past.

In the interior of cars, visual elements are increasingly come to the fore: Number and size of display screens is rising with each new vehicle generation, driven by innovative HMI concepts and the design goal of creating a distinctive signature. Likewise, ambient lighting with selectable and controllable colors is an increasingly popular option. Against the background of this design trend, the ISELED alliance has developed a lighting concept that significantly enhances the design freedom. At the same time, the concept can be used to support technical functions like hazard warnings from an ADAS. The group includes Inova Semiconductor (who invented the APIX protocol family for in-car display connectivity), along with Dominant Opto Techologies (an LED manufacturer with focus on automotive lighting), NXP, TE Connectivity and the University of Pforzheim.

The group developed a string of multiple RGB LEDs (theoretically, up to 4096 triplets would be possible, but the group expects that in reality, some 10 to 30 LEDs will be implemented) which can be addressed and controlled individually through a simple two-wire connection running a high-speed control protocol. As the control element, the system uses an ARM-based microcontroller from NXP. Color and brightness of each LED can be controlled individually. The LEDs are integrated with a relatively simple individual logic device that also stores the exact calibration data of this individual LED – this way, the system can compensate for individual variations, no binning necessary, explains Tek Beng Low, Senior Vice President of Dominant Opto Technologies. “All LEDs have absolutely the same color and brightness”, Low says. The chip also contains three constant current sources – one each for the red, green and blue LED as well as a temperature sensor and the interface circuitry necessary. This chip and the LED triplet come in a package of just 2,8 x 4,1 x 0,65 millimeters. The system offers diagnosis capability and meets the requirements of the safety standard ISO 26262 – this has been necessary because of the link to ADAS systems, says Inova CEO Robert Kraus. Despite is seeming complexity it is cheaper than a comparable system implemented with discrete components which would be the only alternative at the current state of technology, Kraus assures.