The initial resolution of the imaging device is quite limited, the image quality is poor. But as technology evolves, the resolution 300,000 pixel VGA grade progress to 100-2000000 pixels and quickly toward the more than 3 million pixels of resolution level forward. Continued improvement in imaging devices, processors and software, consumers now want to get more digital camera functions, such as the flash in low lighting conditions, even automatic focus. In this resolution, good quality output as well as pictures and video sharing becomes more practical, these higher-density CMOS imaging devices need to get more reflected light from the target, thus further promote the needs of the integrated flash function.
To the traditional Xenon flash placed into a fairly compact size of the phone challenging design engineers, because the thick flash high-voltage capacitors must also be coupled with the bulb and the associated transformers and electronic circuits, while the traditional The flash does not apply to the use of video capture. Fortunately, LED manufacturers have started to improve through the use of new materials such as indium gallium nitride (InGaN) and other power LED lights output.
On the other hand, semiconductor manufacturing technology innovation and package improvements can produce the number of lumens, and photoelectric conversion efficiency. To generate the highest light output, power LED requires 400mA or higher, and pulse width in the current output capacity from 50 to 200ms. However, for video applications, you need a smaller current, but time is not limited to a single pulse. In addition to size restrictions, and ergonomic considerations, these camera modules usually integrated in the rear or top of the screen, so that users can use the LCD as a viewfinder grab image, which is particularly common in the folding mobile phone. Imaging device and the lens bodies may also have to be able to rotate, so that the phone can be face-to-face communication tools as video conferencing mode, is expected to be more common in the design of the 3G network phone because there is enough bandwidth can be used in video conferencing.
Discussion of these trends can be clearly seen become more and more high quality and resolution of the screen display, while the size is also growing, in particular, is a feature-rich multimedia mobile phone is expected that the future will more and more more content such as streaming video or broadcast video, Internet browsing and e-mail, camera and photo viewing, as well as games and access to information services. Therefore, when the phone screen to use when no call more frequently, but if the phone’s battery life is not enough, these functions will be limited. Therefore, the high efficiency of the system power management, including the screen and button backlight power management becomes very important functions such as camera flash past, only to see the high-end phones will gradually become the standard configuration.
These will also have a white LED backlight driving circuit design challenges: bigger screen represents a more regional need backlight, it is necessary to enhance the overall efficiency of the drive device; due to limited space, it must be integrated in a single package multi-function; not only consider the size, the thickness must be reduced, in particular, sliding and folding the shape of products.
Phone white LED tubes driver circuit is frequently used in the two architectures: LED is connected in series inductor boost converter circuit; each LED stable current source to drive the charge pump drive. The inductive solution can bring the best overall efficiency of the charge pump due to the use of small ceramic capacitors as energy conversion devices, the smallest. Figure 1 and Figure 2 shows the typical application circuit of the two driven architecture. At present, the power LED efficiency continue to be improved, reducing the power consumption of the backlight LED, it can provide higher light output with less of the LED. This means that two or three years ago, four LED backlit 1.5 inch screen, now just two power only half of the LED will be able to get the same performance.
To meet this demand, you need one capable of driving two LED new products such as led flood lights, and can support a very low current low-power standby operation of the backlight of the screen. To solve this problem, NCP5602/12 series of charge pump LED driver devices designed to support ultra-low current ICON mode, while the simple single-wire or I2C serial bus provides two LED ordinary backlight. In addition to support for the latest thin and light package trend, these products are designed using very thin LLGA micro packaging technology (2 × 2 × 0.55mm) to support the ultra-thin applications. In addition, part of the improved LED materials and design has a lower forward voltage (reduced from 3.6V to 3.1V), inductive solution, the same power that can drive more LEDs. More complex LED drive device, such as NCP5604A / B has a voltage conversion mode select, provide optimal power conversion at the same time lower power consumption of the integrated current source, the lithium-ion batteries used in mobile power supply most of their working time to reach 85% conversion efficiency (PLED / Pin).
LED flash camera phone configuration, this Semiconductor has developed the NCP5608 multiple-mode charge pump LED driver, which drives four LEDs for the backlight of the main screen and sub screen, and is provided to drive 1W power LED up to the high current output of 400mA. These features are designed to share a high-efficiency charge pump converter circuit, in order to minimize the number of external capacitors.