In addition to their long life, high energy efficiency, and ability to control the light source, LED lighting continues to make inroads into the automotive industry due to its high brightness for safer driving. LED lighting can be mounted or integrated all around a vehicle — front, rear, sides, and even on top. LEDs have been used for some time now in high-mounted brake/stop lights and turn signals, moving into rear combination lights (RCLs) and fog lights.
Automakers are also adding more intelligence to their lighting systems for improved safety. These include adaptive driving beam (ADB) technology that dynamically adjusts high beams based on the environment and “animated” lighting, such as in the cabin for driver-assistance prompts and vehicle status information as well as in lightbars for safety warning, advanced navigation, and blind-spot warning applications.
Automotive lighting is becoming a potential critical node for autonomous driving and could represent a key location for integrating sensors such as local cameras, radar, and LiDAR, according to Yole Développement (Yole).
Yole’s Advanced Front-Lighting Systems report finds that the digitalization of cars is a megatrend in the automotive industry, moving toward electric and autonomous vehicles. This includes new approaches in safety, comfort, and information services as well a greater importance on exterior lighting as the industry moves toward greater communication between all road users.
In terms of LEDs, they are rapidly gaining popularity as their cost decreases and efficiency, luminance, and package size improves, according to Yole, with full LED headlamps now being commercialized in emerging markets and nearly all carmakers and Tier One parts suppliers having developed full LED-based headlamp systems. The report also finds that advanced LED matrix headlights, with more than 50 LEDs per vehicle, have been implemented in premium car segments.
LEDs are also used for ambient lighting in the interior of the vehicle. They are used in a range of applications, such as the dashboard, telematics, door lights, reading lights, climate control systems, and audio/video systems.
Market research firm LEDinside, a division of TrendForce, reports that some suppliers are developing RGB LEDs for interior ambient lighting as part of the intelligent light trend. This enables features such as full-color mixing and dynamic ambience.
Here is a sampling of 10 LED and LED driver innovations for automotive lighting.
LEDs
With the greater adoption of LEDs in headlights, LED manufacturers like Osram Opto Semiconductors continue to work toward improving brightness, energy efficiency, and thermal performance. The company has released several next-generation LED products with improvements for greater safety when driving. These include the latest versions of the Oslon Compact PL and Oslon Black Flat S LEDs.
Osram is launching a new generation of one- to four-chip versions in the Oslon Compact PL product family. Like their predecessors, the ceramic components have an electrically insulated pad that makes it much easier to dissipate heat from the package. This enables a higher current that allows the one-chip version to achieve a brightness value of 395 lumens (lm) at 1 A with a chip area of 1 mm².
With its small size of 1.9 × 1.5 × 0.73 mm, the product is suited for ADB systems and in extremely space-saving system designs. ADB headlights, also called smart headlights, enable greater visibility for the driver.
Osram is also expanding its Oslon Black Flat S family to include one- and two-chip versions. The special lead-frame–based components feature the highest contrast values (>1:200) and very low thermal resistance — which allows for higher currents. The one-chip variant achieves 395 lumens at 1 A. The square lighting surface of the UX:3 chip makes optical design particularly easy for headlight manufacturers.
Osram believes that with the high-efficiency values up to 130 lm at 1 A, it could enable headlights with smaller or potentially no heat sinks in the future. Package dimensions remain the same in the new generations of Oslon Compact PL and Oslon Black Flat S.
Samsung’s FX-Series LEDs (Source: Samsung Electronics)
Samsung Electronics also upgraded two of its automotive LEDs to deliver higher light efficacy. The company’s second-generation C-series and FX-series offer a light efficacy of 133 lm/W, which the company said is among the highest in high-power automotive LED packages. By providing more brightness at a low voltage, the packages also enable the use of smaller heat sinks, allowing for lighter lamp designs, which, in turn, reduce system cost for lamp manufacturers.
The Samsung C-series targets exterior lamps, such as headlamps, which require greater levels of luminous flux and a high degree of reliability, especially when operating under harsh conditions, said Samsung. Featuring up to four multi-chip designs, the C-series solutions deliver as high as 1,560 lm, while the ceramic substrate’s thermal stability and high durability enhance the reliability of each package.
In addition, by incorporating the company’s differentiated phosphor blend, the C-series doubles the contrast ratio to as much as 1,000:1 from its previous iteration, which dramatically improves driver visibility, said Samsung. The C-series is available in a wide range of luminous flux and sizes.
Also claiming highly reliable performance, Samsung’s FX-series, built on a flip-chip–based package, is available in a compact size of 1.8 × 1.4 mm. The FX LEDs enable sleeker designs, thanks to their small size, for applications such as daytime running lamps (DRLs) and head-up displays (HUDs), as well as next-generation ADBs.
Designed for electric vehicle (EV) headlamps, Seoul Semiconductor Co., Ltd. introduced its next generation of wafer-integrated-chip-on-PCB (WICOP) UHL (ultra-high-luminance) series LEDs. The new WICOP UHL LEDs reduce headlamp power consumption by up to 20% for EVs with a 40% improvement in heat dissipation compared with other LED products, according to the company. Mass production will start in 2021.
Battery power consumption is one of the important requirements that determines the driving distance on a single charge, making it critical to reduce the overall weight of the automotive components to reduce power consumption, said the company.
Seoul’s WICOP UHL LED technology (Source: Seoul Semiconductor) Click for larger image.
By using the WICOP UHL technology in the headlights, the weight of the lamp’s heat-sink structure can be reduced by 75%, said Seoul. In addition, the LED-emitting area of the product is extremely small, measuring approximately 0.5 mm2, which enables a slim headlamp design.
The WICOP products are the industry’s first patented package-less LED technology developed by Seoul Semiconductor. “Unlike flip-chip technology that must be bonded in the semiconductor process, WICOP LEDs can be easily surface-mounted (SMT) in the general substrate bonding process,” said the company.
Aimed at automotive interior lighting, Everlight Electronics Co., Ltd. has embedded an intelligent IC driver in its smart LED series to better manage colors and adjust brightness via a controller. The EL SMARTLED (Smart Multi-Function Automotive RGB Technology) Series enables automakers to use a combination of colors in the vehicle’s interior. Everlight is a member of the ISELED Alliance, which focuses on developing smart LED technology for automotive interiors and improving the user experience.
The EL SMARTLED (XI3040-RGBIC0251L-AM) integrates the driver IC into the RGB-LED package, which can control the component calibration color difference in the third-order SDCM (MacAdam Ellipse). The integrated driver IC enables the control of thermal runaway by temperature-sensing the red LED. The EL SMARTLED can gang up to 4,000 LEDs in series via a LIN interface with a transmission speed of up to 2 Mbits/s and claims better color uniformity compared with traditional RGB-LED solutions.
The smart LED is housed in an SMD package, measuring 3.0 × 4.1 × 0.9 mm. Automotive interior applications include interior lighting, roof reading lighting, and dashboard display.
Similarly, Dominant Opto Technologies launched its smart LED series, called seddLED (Smart Embedded Digital Driver LED). The single package integrates the RGB LED, LED driver, and advanced ISELED communication protocol for automotive ambient lighting.
The company’s first part in the seddLED3.0 family is the A3A-FKG-1400-1, which is pre-calibrated to D65 white point with an accuracy within three SDCM steps at 1,400 millicandela (mcd), followed by the A3A-FKG-RGB-1, which is pre-calibrated to individual red, true green, and blue at 400 mcd, 1600 mcd, and 250 mcd, respectively.
The advantage of the A3A-FKG-RGB-1 is that it is able to fine-tune the variation of color and intensity by controlling the LED peak current (PWM), wavelength calibration, and temperature compensation, according to the company.
The company also offers the seddLED3.4 part number A3D-MKG-2000-1, which is pre-calibrated to D65 white point with an accuracy within three SDCM steps at 1,400 mcd.
LED drivers
To take full advantage of LED benefits and achieve the most efficient light output, LEDs have to be matched to the right LED drivers. Here are five drivers that can do the job.
Diode Inc.’s AL8843Q and AL8862Q DC/DC buck converters (Source: Diodes Inc.)
Aimed at driving either single LEDs or multiple LED strings for interior and exterior automotive LED lamps, the AL8843Q and AL8862Q DC/DC buck converters from Diodes Inc. can be used in automotive lighting applications such as DRLs, fog lights, turn lights, and brake/stop lights. Both devices, housed in SO-8EP packages, are qualified to AEC-Q100 Grade 1.
The AL8843Q, with a supply voltage from 4.5 V to 40 V, and the AL8862Q buck converters, with a supply voltage from 5 V to 55 V, can withstand even severe voltage variations, such as load dumps during low cranking or stop-start operation, without suffering any degradation in the LED drive current, said the company. Safety features include overtemperature protection as well as LED short- and open-circuit protection. The AL8862Q also incorporates an open-drain fault indication pin.
The DC/DC buck converters support full-scale (0% to 100%) PWM dimming, controlled with either an analog input between 0.4 V and 2.5 V or a PWM signal generated by an external microcontroller or host processor. Both parts feature an integrated power MOSFET: 40 V/0.2 Ω for the AL8843Q and 55 V/0.4 Ω for the AL8862Q. They also feature hysteretic-mode buck LED driver control, which simplifies the feedback loop, enabling engineers to realize highly stable buck converter designs using only four external components.
Delivering greater functionality for advanced vehicle lighting, ON Semiconductor has released a family of four devices that help simplify the design of advanced vehicle lighting to ensure greater road safety. Aimed specifically at low-power solid-state lighting, the new family is comprised of two LED drivers (NCV7683 and NCV7685) and two current controllers (NCV7691 and NCV7692).
For improved road safety, automakers are moving away from the simple “on/off” operation to sophisticated systems that incorporate movement and variable intensity in RCLs, turn signals, fog lamps, and other externally modulated LED clusters to provide highly visible warnings to other road users, said ON Semiconductor.
ON Semiconductor’s NCV7685 LED driver (Source: ON Semiconductor)
The NCV7685 and NCV7683 integrate 12 and eight linear programmable current sources, respectively, enabling multiple strings of LEDs to be driven with up to 100 mA per channel. A variety of configurability options are available, including daisy-chaining, illumination level control, current regulation, sequencing functionality, and channel combination.
The NCV7685 incorporates an 8-bit I2C interface with CRC8 error detection for individual output current adjustment via PWM, and for advanced diagnostics — including detection of an open LED string or undervoltage condition — a dedicated diagnostic pin is also available. The NCV7685 may be powered with a DC/DC controller and/or LDO voltage regulator, depending on design requirements.
The NCV7691 provides a regulated wide current range for driving LEDs in one or multiple strings, with only an external NPN bipolar transistor and a feedback resistor. The driver allows the addition of additional single channels to multi-channel systems and supports a dimming function via its PWM input. For safe operation, the NCV7691 includes open-string, short-circuit, and thermal-shutdown functionality. The derivative NCV7692 offers a faster response time and a reduced threshold for open-load detection.
For new smart automotive lighting applications, Melexis has developed an RGB-LED driver that incorporates its MeLiBu (Melexis Light Bus) high-speed communication IP that enables intelligent animated automotive interior lighting. The communication interface allows carmakers to improve safety using animated lighting in the cabin for features such as driver-assistance prompts and vehicle status information. These lightbars can be used in safety warning, advanced navigation, and blind-spot warning applications.
The MLX81116 is a fully integrated smart automotive LED driver that offers high-speed communication between multiple LED drivers to enable applications with high LED counts for animated light applications. It includes all of the required components for LED driving as well as communication. It provides real-time update of >250 RGB LEDs without delay.
Melexis said that RGB-LED lightbars can communicate to the driver through color coding, color changing, and blinking sequences, but there are challenges. These include maintaining consistent color across all the LEDs in the lightbar and ensuring they all change simultaneously.
Melexis’s MLX81116 driver IC (Source: Melexis)
The company’s answer is the new MLX81116, which addresses these issues with its high-speed communication interface IP. The MeLiBu controls all individual LEDs separately in the lightbar to produce the lighting effects while providing real-time compensation of any LED color drift caused by environmental changes.
The MeLiBu communication interface is based on the CAN-FD physical layer, which ensures robustness, reliability, and high speed (up to 2 Mbits), said Melexis. The interface supports dedicated optical parameters that allow color-mixing accuracy with a delta UV of 1% to ensure no distinguishable differences between individual LEDs in the lightbar. It also provides temperature compensation without additional external components.
The MLX81116 driver IC has a wide dimming range that allows for brightness adjustment for daytime and nighttime driving. It meets automotive ISO 26262 functional safety requirements up to safety integrity level B (ASIL B) and features low EMI emission and high immunity, thanks to the use of the CAN-FD physical layer, which eases compliance with applicable EMC regulations, said Melexis.
Also designed for animated lighting for automotive applications is the IS3xFL3265x family of LED drivers from Lumissil Microsystems, a division of ISSI. These LED drivers feature high-voltage LED channels with electromagnetic compatibility (EMC) reduction capabilities.
Designed for harsh and demanding environments, the LED drivers integrate registers to adjust thermal protection levels with fault detection and reporting and operate across a wide temperature range of –40°C to 125°C. These LED drivers are suitable for automotive and industrial applications that require high-voltage LED outputs to support a multi-count stack of LEDs per channel.
The drivers support 18 high-voltage LED outputs, which can be individually configured for optimal light output, whether performing RGB color or white illumination lighting, according to Lumissil. The high-voltage outputs enable design engineers to stack multiple LEDs on the same channel for an increase in light output using a given LED current.
Lumissil’s IS3xFL3265x family of LED drivers (Source: Lumissil Microsystems) Click for a larger image.
For interior and exterior automotive LED lighting, the LED drivers feature a flexible bus architecture and built-in EMI suppression technology. The I2C or SPI bus protocols are supported by selecting the corresponding part number — IS32FL3265A for I2C or IS32FL3265B for SPI bus. The core functionality of high-voltage outputs, individual channel (zone) lighting control, EMI suppression, fault protection, and AEC-Q100 compliance is common for either bus interface.
For interior ambient lighting designs, the 18 high-voltage channels can be configured for six RGB zones or 18 high-brightness lighting zones. For exterior applications, the 18 individually controllable LED channels can be configured to create lighting effects for “welcome light” or animated tail-light applications.
Aimed at a broad range of socket-type LED lamps used in vehicle systems, including DRLs and position lighting to rear lamps, Rohm Semiconductor’s BD18336NUF-M ultra-compact high-output linear LED driver provides stable lighting even in the event of battery voltage drops on a single chip. It also helps shrink the size of the latest socket-type LED lamps.
Socket-type LED lamps that can be replaced as easily as LED bulbs have garnered a lot of attention by offering superior maintainability, said Rohm. However, it is difficult to decrease socket size, creating issues around design flexibility.
The BD18336NUF-M uses a current bypass function that prevents LED turnoff and maintains a brightness of at least 30% at all times by switching the LED current path, even when the battery voltage decreases from 13 V to 9 V. Rohm said it is the first single-chip to incorporate a current bypass function that enables stable lighting during battery voltage drops.
In addition, a high output of 600 mA is achieved in an ultra-compact 3.0-mm2 package, and the mounting area is reduced by about 30% over conventional solutions (including the external circuit), said Rohm, making mounting possible on the 10-mm2 substrates required for small socket-type LED lamps. The built-in current bypass function reduces the number of external parts by seven over conventional designs, enabling the smaller mounting area.
A function for suppressing LED heat generation is also built in that supports white LEDs that typically run hot, allowing them to be used in DRLs and other vehicle lighting systems utilizing white LEDs.
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It’s available now at the EE Times bookstore.
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Learn more about Diodes IncorporatedMelexis Microelectronic SystemsON SemiconductorOsram Opto SemiconductorsROHM SemiconductorSamsung ElectronicsSeoul Semiconductor
