LED rear lighting
Solutions for Automotive LED rear lighting system – architecture solutions and LED driving concepts
Exterior Lighting, LED Front & Rear Lighting, is not only one of the key differentiating factors for car-makers as a brand recognition but as well an important part of safety, reliability, energy efficiency and the so-called “User Experience: UX” (emotional identification). As more and more dynamic and animation functions have come to the Rear Lighting System, the complexity for supply, communication, sense, control, and actuation has been continuously increasing. To keep this complexity manageable in terms of space on the PCB but also in terms of power dissipated, the integration of functions and scalability of products became a key factor for the design.
Infineon offers dedicated solutions for LED control with a benefit from low power consumption and low quiescent current under the brand name of LITIX™, the best-LED Driver IC to benefit from the advantages of LEDs while providing full protection to your application. The LITIX™ family is a success story of several generations of LED Drivers:
- LITIX™ Linear are designed to supply constant current up to 500mA, which enables constant LED brightness and ensures extended LED lifetime, independently from supply voltage or LED forward voltage class. LITIX™ Linear are the best solution for automotive interior LED lighting as well as LED taillights and indicating LEDs when diagnostic is required
- LITIX™ Basic are optimized for the control of low to medium power LEDs in automotive applications. The whole family of linear constant current sources offers footprint compatibility ranging from 1 to 3 output channels and 60-180mA and enables stable and reliable LED brightness by precise current control.
- LITIX™ Basic+ serve as a perfect extension to the existing LITIX™ Basic family. LITIX™ Basic+ linear constant current sources with their 1 to 3 inputs/outputs build a scalable family to reduce system costs (e.g. less external components needed, the introduction of power shift feature). Output currents from 5 mA up to 360 mA (with power shift) can be served. LITIX™ Basic+ offers the most flexible Single LED Short (SLS) feature in the market: the device can either go to a latched off-state, active retry, or simply diagnosis without channel deactivation.
Infineon's solutions for automotive rear LED lighting
- SPIDER+ LED for resistor-based solutions
- LITIX™ Linear for high power stop light functions
- LITIX™ Basic for tail light functions
- LITIX™ Basic for cost and space optimization
- LITIX™ Power
- LITIX™ Power Flex
The lighting system of a vehicle consists of lighting and signaling devices mounted in the front, rear, sides, interior and on top of the vehicle. In the rear, it signals the presence, the direction of travel, the position and the size of the vehicle.
Overall it provides greater safety in road traffic.
The rear lights are integrated into the trunk or in the car fender – sometimes in both places.
Rear lights include:
- tail lights to signal the presence of the vehicle which are activated when the headlights are on,
- stoplights indicating that the vehicle is slowing down,
- reversing lights which signal that the vehicle is moving rearwards,
- rear fog lights signaling the presence of a vehicle when the view is below 50m,
- turn lights show the intention of the driver regarding direction right or left,
- center high mount stop light to indicate when the vehicle is slowing down and
- license plate light to illuminate the vehicles license plate
A resistor can act as a current limiter, but not as a current control circuit for LED.
Advantages:
- it is a simple solution
Disadvantages:
- results in higher power losses
- the resistor needs to be defined for maximum supply voltage conditions (lower LED current leads to a visible decrease of brightness for example during start-stop-operation)
- no intrinsic overvoltage protection nor temperature protection (results in a reduced lifetime of LEDs)
- additional circuits needed for diagnostics
- limited LED chain length depending on the LED forward voltage and minimum supply voltage
A linear current source provides a constant output current to the LED over the entire supply voltage range as well as diagnostic functions. The LED current is controlled by the linear current source and is easily adjusted with an external resistor. The output current is constant and independent from the supply voltage
Advantages:
- LED can be used in nominal operation conditions with full brightness
- Stable brightness is ensured over full supply range, also during start-stop-operation
- Enables extended lifetime with integrated overvoltage and high-temperature protection, advanced integrated diagnostic features
Disadvantages:
- high power losses possible
- limited LED chain length depending on the LED forward voltage and minimum supply voltage
A DC-DC converter is combined with one or more linear current sources to provide an output voltage which is optimized for the required LED chain length. The DC-DC output voltage is converted into a constant output current by the linear current source which allows for a more efficient LED control.
The LED current is controlled by the linear current source. The DC-DC converter output voltage is adjusted to the LED’s forward voltage which enables numerous topologies (Buck, Boost or SEPIC). Via the different topologies requirements of the LED chain length and voltage range can be met. The output current is constant and can be easily adjusted by an external resistor.
Advantages:
- Higher efficiency than the pure linear current source solution
Disadvantages:
- Increased component count
- PCB layout needs to be optimized for EMC performance
During the past years, LEDs became the first choice in rear lights; this strong increase of LEDs in the different rear light functions requires advanced diagnosis features for the LED drivers in use.
Automotive rear lighting systems include greater signaling. Stylization and personalization like animations are state of the art. Infineon Technologies is supporting this LED rear light success story with several generations of LED drivers: LITIX™ Linear, LITIX™ Basic and LITIX™ Basic+.
LITIX™ Basic+ linear constant current sources with their 1 to 3 inputs/outputs build a scalable family that enables both, a complete set of diagnosis functions (e.g. best-in-class single LED short diagnosis) as well as reduced system costs.
myInfineon: Join now and enjoy the benefits
In this training, you will:
- Be able to identify solutions for rear lighting architecture challenges and understand the usage of smart linear drivers, and
- Get to know the key features and benefits of using TLD7002-16ES for dynamic rear lighting solutions
In this training, you will understand:
- the different LED driving concepts
- get to know the Infineon solutions regarding automotive rear LED lighting
- Recognize Infineon’s set of LED driver families for automotive rear lighting
- Apply Infineon’s chip-set in a conventional rear lighting architecture and its extension for dynamic effects
