Automotive LED lighting not only creates a stylish vehicle appearance and a personalized atmosphere, but also plays an important role in fuel economy and active safety. Advanced lighting solutions automatically dim and steer according to driver's operation, road conditions and environmental conditions to enhance driving safety. As the world's second-largest non-microcontroller automotive semiconductor supplier and the largest automotive adaptive headlamp supplier, ON Semiconductor offers a comprehensive range of energy-efficient LED automotive lighting solutions for automotive interior lighting such as reading lights, RGB Ambient lights, dashboard backlights, etc., and external lighting such as headlights, daytime running lights (DRL), turn signals, taillights, signage lights, etc. This article will highlight its latest innovations. According to system integration and design complexity, lighting solutions can be divided into 4 categories: The most integrated, most complex, and system-integrated solution, not only integrated switching power supply (SMPS) modules, but also integrated various communication interfaces and rich diagnostic functions, mainly for automotive headlamp applications; SMPS with high integration and complex design, mainly for DRL applications; Highly integrated but relatively simple linear LED driver, mainly used for small current brake lights, tail lights, etc.; The simplest discrete device System integrated LED headlights ON Semiconductor has introduced three generations of drive solutions for LED headlamp systems. Both the first-generation NCV78663 and the second-generation NCV78763 use a single-phase boost + dual buck architecture. One chip can drive two strings of LEDs, and has been widely used in major manufacturers such as Mercedes-Benz, BMW, Audi, Renault, and Ford. The third generation scheme According to the latest trend of the LED headlight system, the boost and step-down circuits are divided into two chips, which are suitable for matrix lamp system of multiple strings of LEDs, and the multi-channel buck regulators NCV78723 and NCV78713 respectively. It can drive two strings and one string of LEDs. The two-phase boost regulator NCV78702 and the three-phase boost regulator NCV78703 provide better performance and greater output power. 1. Smart Power Ballast and Dual LED Drivers NCV78663 and NCV78763 The application block diagram of NCV78663 is shown in Figure 1. The Boost controller is connected with an N-channel MOSFET to boost the battery voltage up to 60 V. The Buck circuit integrates MOSFETs to stabilize each string of LED currents (up to 1.2 A). The string LEDs are equipped with temperature detection inputs. The chip integrates multiple diagnostic and protection functions. The SPI interface can be used to communicate with external MCUs or through an internal one-time programmable (OTP) ROM. Figure 1: LED ballast NCV78663 application circuit diagram The NCV78763 boosts each string of LED currents up to 1.6 A, providing higher dimming resolution, and Boost's loop compensation is changed from digital to analog. Since the internal OTP is removed, it must work in conjunction with the MCU at a lower cost than the NCV78663. Figure 2: NCV78763 application circuit diagram The NCV78663 and NCV78763 have the same topological structure and are composed of one Boost + two-way Buck. To avoid flicker effects when using PWM dimming, automotive OEMs typically require dimming frequencies above 500 Hz. In this buck-boost two-stage architecture, the LED is stabilized by the Buck circuit, which can easily increase the dimming frequency and meet the requirements of the OEM. Due to the design requirements, the number and power of LEDs of different models are different, resulting in different voltage and current of LED strings. The buck-boost topology can support a wide range of LED load changes. By changing the value of the corresponding register, it can adapt to different LED load conditions, support for platform design. With the buck-boost topology, the system is easier to stabilize: the Boost circuit is relatively unstable, the system bandwidth is low, and the response is slow, so it is used for boosting in the front stage; the Buck circuit is easy to stabilize, high bandwidth, fast response, and used for the latter stage. The LED is steadily flowing, and the system is very stable even if the LED load has a large modulation. In addition, in the application of adaptive smart matrix headlights, in order to avoid the discharge current from the output capacitor, the output capacitance of the LED driver must be very small. According to the topology, Buck is an ideal current source, and the output has an inductance even if the output capacitor Very small or even zero, and also a small output current ripple, so this buck-boost two-stage topology also supports pixel or matrix headlights. Both NCV78663 and NCV78763 have high integration, integrated switching, dimming, diagnostics, current detection and other functions, and the cost is very competitive. 2. Matrix headlight system solution In the application of matrix headlights, more strings of LED lights are needed. The NCV78663 and NCV78763 can only drive two strings of LEDs per chip. If you drive more strings of LEDs, you need to use multiple chips, which will increase the cost of the solution. The third-generation solution of ON Semiconductor separates the boost chip from the buck chip. The first stage uses multi-phase boost boost to provide greater power. The second stage uses a buck chip that can be used according to the required LED string. The combination of quantities is more flexible and less expensive in multi-string LED applications, and the OTP ROM is integrated internally, so it can work independently without the MCU. For example, the three-phase boost controller NCV78703 can easily achieve output power of more than 150 W, and better performance, such as better dynamic response, lower output ripple, etc., and can reduce passive in high-power applications. Device specifications and solution costs are more advantageous. The NCV78703 can also be connected to separate outputs, with precise control of the power distribution of each phase through the corresponding registers. The dual buck regulator NCV78723 eliminates the need for an external current sense resistor and controls the internal MOSFET's peak current to achieve constant current and high current regulation accuracy. Figure 3: NCV78703 application circuit diagram Switching power supply for LED drive 1. Low reference 8-pin step-up switching power supply The NCV8873 is a boost controller with peak current mode control. It can implement various topologies such as flyback, SEPIC, etc. The feedback voltage reference is only 0.2 V, which is beneficial to reduce the power consumption of the LED current sampling resistor. The input voltage range is from 3.2. V to 40 V, withstands 45 V load-dumping voltage, with a maximum junction temperature of 150 °C, suitable for daytime running lights and backlights. The switching frequency of the NCV887300 is 1 MHz. The high frequency can reduce the volume of the passive components. The switching frequency of the NCV887301 is 400 kHz. The low frequency can improve the energy efficiency and EMI performance. Figure 4: NCV8873–SEPIC for daytime running lights 2. 1.5 A multi-topology constant current LED DC-DC switching regulator The NCV3065 is an LED driver with integrated internal power transistors that can be flexibly configured for various topologies such as boost, buck, and buck-boost. The feedback voltage is as low as 235 mV, which reduces the power consumption of the current sense resistor. The input voltage ranges from 3 V to 40 V, no loop compensation is required, and the operating frequency can be adjusted to 250 kHz for low cost LED drivers. The NCV3066 adds an ON/OFF pin to the NCV3065 and can be used for PWM dimming. Linear LED driver solution for low current applications Linear drives are simpler than switching power supplies and are easier to design, but produce higher power consumption for low current applications. Constant current source CCR A chip can drive a string of LEDs. Typical products are NSI45xxx, NSI50xxx, NSIC20xx, NSI45xxxJ, etc., current from 20 mA to 160 mA, fixed current and current adjustable version, can be used for central high-position brake lights, tail lights, reading lights, etc., only need to be connected in series with LED strings . 2. LED pre-driver For example, the NCV7691 requires an external power transistor to drive multiple strings of LEDs. The device sets the current value through an external current sampling resistor, and integrates short-circuit detection, PWM dimming, diagnosis (undervoltage, short circuit, open circuit) and other functions, external NTC resistor to achieve temperature control, automatically reduce LED current when the temperature is too high To avoid damage. The diagnostic pins of the NCV7691 can be connected together. When any one chip reports an error, the system can respond to turn off other strings. 3. Multiple strings of LED drivers The NCV768x series, such as the NCV7680, can drive up to 8 strings of LEDs, primarily for taillight applications. The NCV7681 and NCV7683 are the next generation of the NCV7680. Each string of current capability is increased from 80 mA to 100 mA. The NCV7683 has built-in timing control that enables the flow of lights without the need for an MCU. The NCV768x family of devices integrates diagnostics with an external pre-buck MOSFET to reduce power consumption and reduce chip heat. 4. Internal lighting single chip solution The NCV7430 is a single-chip red, green and blue (RGB) LED driver with a LIN protocol communication interface that can be programmed for LED color and brightness parameters for automotive interior or ambient lighting, providing flexibility and reduced cost. Simple discrete device: LED shunt The solution to keep a string of LEDs steady is to provide a shunt for each LED or group of LEDs. When any one LED is broken, the LED shunt will be broken down as the voltage rises, bypassing the LED, so that the LED string can continue to work and extend the usage time of the lamp. According to different breakdown voltages, there are shunt chips connected in parallel with one LED, two LEDs and three LEDs. For example, NUD4700 is connected in parallel with one LED, NUD1015 is connected in parallel with two LEDs, and NUD1025 is connected in parallel with three LEDs. In some "mission-critical" headlight applications, when an LED fails, all LED strings need to be turned off, prompting the customer to change the lamp immediately. The low current HBL5006 series helps detect open circuits and triggers the circuit to turn off the LED driver. to sum up LED lighting not only provides the advantages of automotive design, enhances sales appeal and enhances brand image, but also helps control energy and maintenance costs. It can also be used in advanced driver assistance systems (ADAS) to improve safety. ON Semiconductor offers a comprehensive range of energy efficient automotive LED lighting solutions, including LED matrix headlamp system solutions, switching power LED drivers for daytime running lights, linear drives for taillights, and linear solutions for timing lamps with timing control And LED shunts that enhance safety and reliability, and in line with market trends to promote the next generation of automotive lighting innovation. Shenzhen Xcool Vapor Technology Co.,Ltd , http://www.xcoolvapor.com
