Three classic driving solutions light up automotive LED lighting applications with a penetration rate of 90%

[Introduction]Market research data shows that the global penetration rate of LED headlights will exceed 60% in 2021, and the penetration rate of new energy vehicles will be as high as more than 90%. With the dual growth momentum of the increase in car market shipments and the increase in the penetration rate of LED lighting, it is estimated that the output value of the global automotive LED market will reach US$3.51 billion in 2021, with an annual growth rate of 31.8%, showing that LED headlights and automotive displays LED products are still the main driving force for the growth of the automotive LED market. LEDs are widely used for backlighting of displays in navigation and entertainment equipment, as well as for interior and exterior lighting in automobiles, such as daytime running lights, tail lights, and more. Today, automotive intelligence and electrification are increasingly becoming the main trends. The use of high-efficiency and high-performance LED lighting design can bring improvements to automotive lighting, smart cockpits, and human-machine interfaces. Three solutions are provided as examples to provide automotive LED circuit design ideas.

High dimming ratio LED driver to ensure driving safety

LED backlights used in automotive head-up displays, infotainment systems, and instrument cluster lighting must be bright enough to compete with the direct sunlight that floods into the car during the day, but also reduce the brightness by orders of magnitude to avoid Instantly blinds the driver at night. Common LED drivers are powerless to achieve such a high dimming ratio.

The LT3932 synchronous buck LED driver with an integrated 36V, 2A switch has a high PWM dimming ratio. The LT3932 houses its high-efficiency integrated power switch in a small outline 4mm x 5mm QFN package and operates at up to 2MHz switching frequency for compact high-bandwidth designs. Its internal PWM generator can be used to generate a 128:1 PWM dimming ratio controlled by a simple DC voltage when high dimming ratio capability is not required and simplicity is a primary consideration. With built-in fault protection to handle open and shorted LEDs, and spread spectrum frequency modulation designed to help reduce EMI, the LT3932 meets the demanding requirements of automotive and industrial LED lighting applications.

Three classic driving solutions light up automotive LED lighting applications with a penetration rate of 90%

2MHz Automotive LED Driver with Low EMI and Internally Generated PWM Dimming and 90% Peak Efficiency Over Input Range (~91% Efficiency Without EMI Filter)

Driving of the whole headlight group based on a four-switch buck-boost controller

The traditional way of driving an entire headlight cluster with multiple drivers not only complicates the bill of materials and production process, but also makes it difficult to meet EMI standards. Each additional driver adds its high frequency signal to the interweaving EMI, complicating EMI certification, troubleshooting and mitigation. It had to be small and versatile so that it could easily fit into the very constrained spaces of the lamp cluster, and produce very low EMI, minimizing R&D effort and eliminating the need for expensive EMI metal shielding enclosures. Also, it should be efficient.

Take ADI’s synchronous, four-switch buck-boost LED controller, the LT8391A, for example, which provides a solution that meets all of the above requirements and can drive an entire headlight cluster, all with a single controller. Specifically designed for automotive headlamps, the LT8391A LED driver uses AEC-Q100 components and meets CISPR25 Class5 radiated EMI standards. Spread spectrum frequency modulation reduces EMI and also performs flicker-free operation while performing PWM dimming, and requires only small inductors and extremely small input and output EMI filters. For the 2MHz converter, there is no need to use a large LC filter, and only small ferrite beads are used to reduce high frequency EMI, which is a great advantage.

Three classic driving solutions light up automotive LED lighting applications with a penetration rate of 90%

A 2MHz demo circuit DC2575A using the LT8391A drives a 16V LED at 1.5A.

Automotive EMI requirements are not easily met with high power converters. High-power switches and inductors placed on large-area PCBs and close to large capacitors can create undesirable hot loops, especially when a large sense resistor is included. The unique LT8391A buck-boost architecture removes the sense resistor from the buck and boost switch pair hot loops, resulting in low EMI.

As can be seen from the figure above, the LT8391A 2MHz, 60V buck-boost LED driver controller powers LED strings in automotive headlamps. Features of the device include its low EMI four-switch architecture and spread spectrum frequency modulation. Designed to meet CISPR 25 Class 5 EMI specifications. In addition, the device’s unique high switching frequency allows it to operate at frequencies above the AM band, requiring very little EMI filtering design.

Design of high-brightness LED driver circuit for automobile daytime running lights

The development of high-brightness LED technology has made the advantages of contrasting with traditional lighting technology more obvious – more environmentally friendly, safer, more energy-efficient, and can improve the appearance and design of the car’s interior, and have a longer service life. In the past, designers have not been able to optimize for efficiency, minimal external component count, minimal EMI, and wide-range PWM dimming due to the limitations of high-brightness LED drivers. The above technical bottleneck can be solved with the introduction of high-performance multi-string LED drivers like the MAX16814, which enable bidirectional communication between the switches and linear controllers of these drivers.

The MAX16814 can drive up to 4 strings of LEDs at up to 150mA per string, greatly reducing the number of external components. In addition, the MAX16814 has complete fault protection measures and detection functions. When any string of LEDs has an open circuit or a short circuit, the operation of this string will be turned off, and a fault alarm output will be sent to the system. The figure below is a design example of a complete automotive head-up Display or driving light driver subsystem. The circuit includes all external components and input EMI filters. With the low noise characteristics of the MAX16814, the external EMI filter components can be very small.

Three classic driving solutions light up automotive LED lighting applications with a penetration rate of 90%

The MAX16814 boost switching converter and linear current sink regulator section can communicate bidirectionally instead of operating independently. Its communication capabilities help achieve greater efficiency and avoid the problems faced by many traditional drives. A car’s daytime running lights and head-up displays have the same performance requirements: stay on while the car is in motion, requiring high reliability/redundant design to ensure normal operation in all conditions. The bidirectional communication capability of the MAX16814 also avoids problems caused by failed or open LEDs. Once an LED fails, VBOOST begins to rise, and when the voltage reaches the OVP threshold, the failed string can be identified and disabled or removed from the AVO control loop. string, other LED strings keep working normally. In addition to reducing the brightness of the lighting, there will be no other impact on the user.

Author: Yoyokuo