The automotive LED driver IC market is highly competitive, and manufacturers' core competitiveness lies in the features of their products, that is, achieving differentiated design while meeting basic functional requirements.
For example, recently, ROHM, a major automotive LED driver manufacturer , launched the industry's first LED driver "BD18336NUF-M" for many socket-type LED lights such as automotive DRLs (daytime running lights), position lights and tail lights . The feature is that when the vehicle battery is undervoltage, only one chip can achieve safe lighting, which helps to miniaturize the latest socket-type LED lights for DRLs and position lights.
So, how does the product achieve this function? What are the characteristics of the automotive LED driver? Mr. Ge Jiaming, Product Application Manager of the Technology Center of Rohm Semiconductor (Shanghai) Co., Ltd., gave a detailed introduction to the Electronic Products World and other media.
Ge Jiaming, Product Application Manager, Technology Center, Rohm Semiconductor (Shanghai) Co., Ltd.
1. Features of BD18336NUF-M
Currently, maintainable ultra-small socket-type LED lights are very popular, and the new product "BD18336NUF-M" released by ROHM this time is a driver for driving such LED lights. The specific working characteristics are: when the battery voltage drops from 13V to 9V, the newly equipped undervoltage current bypass function is used to prevent the light from going out by switching the LED current path, and the brightness can always be maintained at more than 30%. In addition, a high output of 600mA is achieved with an ultra-small package of 3.0mm square.
Compared with previous products, ① the new solution, including peripheral circuits, has a mounting area reduced by about 30%, and can be installed in a 10mm square circuit board required for ultra-small socket-type LED lamps. ② If the previous product is used without peripheral circuits, when the battery is undervoltage, the LED lamp will go out, posing a safety hazard to the surrounding environment. The new product can help socket-type LED lamps achieve safe lighting and miniaturization with only one chip. ③ In order to support high-brightness white LEDs that are prone to temperature rise, the new product also has a built-in function to suppress LED heat, making it suitable for DRLs using white LEDs.
Samples of the new product began to be sold in December 2019, and mass production is scheduled to begin in July 2020 at a temporary scale of 400,000 units per month. The chip's front-end process is in Japan, and the back-end process is in Rohm's Philippine factory.
1.1 New socket-type LED lamp and circuit board
Due to the long life and high-density installation characteristics of LED lights, they are currently being used very rapidly in the field of automotive lighting. However, previous product designs can achieve more complex performance requirements, but lack maintainability. As shown on the left side of Figure 1, the previous solution was to install a large number of components on the circuit board to achieve the diversified design and higher performance requirements of automotive LED lights. However, customers are no longer satisfied with this status quo, and the requirements for maintainability are also increasing. Socket-type LED lights that can be easily replaced like light bulbs have begun to appear, as shown on the right side of Figure 1.
figure 1
1.2 Disadvantages of socket-type LED lamps and solutions
However, socket-type LED lights face two major issues. First, the size of the socket itself limits the flexibility of customers in design. Second, the circuit board area is very small, so it cannot accommodate enough components, causing the LED lights to go out when the battery voltage is low, which still poses a considerable risk to the driving safety of the surrounding vehicles.
To address this issue, ROHM has launched an ultra-small, high-output linear LED driver IC, the new product BD18336NUF-M. With the launch of this new product, "it is expected that car lighting manufacturers around the world will begin to popularize this design," said Ge Jiaming.
figure 2
Its main functions are shown in red in Figure 2: ① Current bypass function when the vehicle battery is undervoltage; ② Output current derating function.
1.3 Principles of the two main functions
1) Current bypass
The new product released this time has the following features. First, the single-chip solution can realize safe lighting when the vehicle battery is undervoltage. Figure 3 is a working diagram. After being configured through three external resistors, the battery voltage can be monitored. When the battery voltage is under normal working conditions such as 13V, the constant current LED driver BD18336NUF-M can output current normally to ensure that the load - 3 LED lights are lit. However, when the vehicle battery voltage drops downward, for example, in an undervoltage state below 9V, due to the current bypass function when the chip is equipped with an undervoltage, the bottom LED in the load can be bypassed to ensure that the remaining 2 LED lights are lit at the brightness expected by the customer; and the switching from lighting up 3 lights when the battery voltage is sufficient to 2 lights under undervoltage is a smooth and stable process, and there will be no flashing of lights. This helps customers' new socket-type LED lights to meet their safety design and miniaturization requirements.
Figure 3 Current bypass function during undervoltage
Figure 4 is a detailed explanation of the LED lighting situation. For previous products, if three LEDs are driven, the voltage drop is about 9V when the three LEDs are turned on. When the battery voltage is below 9V and undervoltage reaches 6V, the three LEDs cannot be turned on, which will cause a safety hazard of the lights going out. After the new product is installed, within the working range of undervoltage 9V-6V, the two LEDs can be lit, and the safety requirement of more than 30% brightness of the socket-type LED lamp module can be guaranteed.
Figure 4 Schematic diagram of lighting compared to previous products
The current bypass function can be seen in Figure 5, right. The red current curve is a current curve when the vehicle battery is depleted. It can be seen that when the battery voltage drops from the normal 13V to 6V, the current bypass circuit built into the new chip starts to start, and its working range can be configured through external resistors. It can be seen that the red circuit curve during power reduction is in a linear rising process, which means that the peripheral bypassed LED3 will gradually go out. Finally, when the battery voltage drops to 6V, it can still ensure that the two LEDs are on.
Figure 5 Working effect of current bypass
2) White LED - Over-temperature derating function
In addition to the traditional yellow and red lights, the new product BD18336NUF-M also takes full consideration of the application of white light, making it suitable for all LED light colors including high-brightness white LEDs.
Figure 6
As we all know, the power of white LED is relatively large, and there will be temperature rise. The chip has been equipped with an over-temperature derating function. The customer can achieve the function of reducing the output current by simply configuring a thermistor on the periphery. For example, a 100kΩ thermistor can start to reduce the current at around 110℃; a 47kΩ thermistor can start to reduce the current at a temperature of 85℃, which greatly expands the application range of the product - in addition to the traditional red and yellow light taillights and position lights, it can also be used in white light LED applications such as daytime running lights and fog lights.
3) Related issues
Is the cost of socket-type LED lamps higher than before? Is it more difficult to manufacture? Manager Ge Jiaming pointed out that the manufacturing difficulty of socket-type LED lamps is not much different from that of PCB boards.
The number of PCB boards for installing socket-type LED lamps has been reduced, so is the PCB design still the same as before? In fact, for conventional designs, customers can use ordinary epoxy resin FR4 boards, or consider heat dissipation and add some heat sink design requirements, or carry some ceramic board designs, which are all possible.
Will the supply and field engineer services be affected by the epidemic? "Please don't worry about this. Our supply is still relatively normal. For field engineer services, considering the current situation, ROHM and customers' support is still mainly online. The next step will depend on the development and control of the epidemic." Manager Ge Jiaming said.
2 Car LED Driver
LED driver IC is an IC that provides a constant current to the load LED lamp for unstable input voltage, such as the battery on a car, so that the brightness of the LED lamp can be constant or adjustable.
Figure 7
Car LED lights can be divided into two categories of applications: body lighting and interior lighting. Body lighting includes headlights, daytime running lights, taillights, and turn signals, while interior lighting mainly includes car audio, navigation, air conditioning panels, RGB ambient lights, and dashboard warning lights.
ROHM has relevant IC layout in both of these areas, so it can control all car lights.
3 Power supply technology helps LED drivers
ROHM has strong strength in automotive power circuits and can contribute to the miniaturization and simplification of user designs. Its power technology can be roughly divided into three aspects: DC/DC, AC/DC technology, linear LDO technology, and this time, LED driver technology.
Figure 8
In terms of LED drivers, ROHM has the following key technologies:
• Surge suppression techniques;
• Control techniques for frequency stabilization;
• Linear control, which is the technology involved in the new product BD18336NUF-M;
• Local dimming function;
• Noise reduction technology.
4 ROHM's LED driver production and patents
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