Today will be the portable consumer electronic devices and compared to previous years, you will understand why the lighting has become a major power management challenges. LCD panels with a single passive devices are rapidly being eliminated. Now all the equipment with high-performance, high-resolution, 2.5 to 3-inch diagonal color display, to support ranging from Internet access and mobile TV to the video playback of the entire scope of the application.

Typical of these displays need four or more for the LED backlighting and drive. Many handheld devices (especially the clamshell design) are increased by a smaller Vice display, showing time, date and connectivity, and other basic information. Under these main display screen usually need more than 1-2 for LED backlighting feature.

With the stylish lighting design engineers found that differences in the products of the important role of many of today's portable electronic equipment will need additional power circuit to drive the state-assisted RGB lights and backlit keyboard.

Built-in camera with a higher degree of complexity of the power circuit design. These features are generally offered by the high current in a very short duration of the drive to provide a small LED flash. But when the handset manufacturers to introduce the beginning of this function, they are used less than 1 million pixels of the CCD, which requested the current flash drive no more than 100 mA. Today's handheld devices integrated design engineers are much higher resolution of the CCD, such as high as 600 mA CCD requirements will only be used to drive the current flash functions and provide sufficient light to obtain high-resolution photos. The film features such as flash mode and more new features due to the need for more low power LED driver for a longer duration, and an increase of the power circuit design more difficult.

Taking into account these factors, it is easy to understand why the lighting is usually the most handheld devices in the source of the battery consumption. Previously, design engineers through the use of boost converter or on a separate charge pump to provide them to achieve the lighting function. But with the increase in the number of functional lighting and power requirements of the increase, design engineers need to better control the strength to deal with light, color balance and management to increase the maximum power. Eventually these engineers to use system for micro-controller or controller, through the PWM (PWM) control to solve these problems.

More simple design

In recent years, the power management integrated circuit (PMIC) manufacturers have developed various aims to provide higher-level engineers to control and simplify the design of the IC. To National Semiconductor (NS)'s LM27965 example, the white LED (WLED) driver can drive up to nine parallel LED, the total output of up to 180 mA. To the greatest degree of design engineers to improve the ability to control, forward current output can be divided into 2-3 separate control group, and configure 4-5 to backlight LED-based display; configuration 2-3 LED display for the vice Provide backlit screen; allocation of a single independent control of the drive to manage the state or indicator LED. Each LED through a standard I2C interface control.

Although based on the induction boost converter solutions are still many applications demonstrated advantage. However, in many cases, manufacturers have begun to use mixed-mode charge pump to drive or scores of compact portable applications in the WLED, and no longer need the sensors. Although the fixed charge pump boost in output is a separate resistance modulation, but the LED current matching and efficiency may be affected. A mixed-mode charge pump, the output voltage can be modulated to maintain a constant current of each LED, making design engineers more accurately match current source.

With many competing products similar to that of Stuart Ling (Linear Technology) company in August released LTC3219 using multi-mode charge pump, the device can be an on-times mode, and then when any enabled LED current source close to voltage drop Automatically switch to boost mode, or 1.5 times.

Then the voltage drop of the device to switch to double (2 x) model. In support of the main screen and RGB lighting requirements, the device can drive the nine separate allocation of the current source.

NS with the device, the transit of Stuart devices in each current source through the two-lane I2C serial interface using digital control of gray, brightness, flashlight and classification regulation.

Early WLED need relatively high forward voltage and current to achieve the desired degree of light. However, recent technological advances have allowed manufacturers in the following 10 mA current work of the WLED. These devices can be in the positive than the previous low voltage work. Recent technological developments have allowed PMIC manufacturers started to provide independent linear match the current source, because most of the external device no longer need to lower costs and reduce the footprint.

For example, again, TI's TPS75105 to provide a four-channel LDO, and in an extremely tight 1.2 กม 1.2mm package, the two slot with up to four LED matching LED constant current drive. The product is no longer required for induction boost converter of sensors, the output capacitor and / or feedback resistor, or to use mixed-mode charge pump to achieve the stability required for switching capacitors and input / output capacitor.

Cameras flash drive is a more difficult challenge. Design engineers must be provided within the time frame provided adequate light, and no more than the power to restrict or limit LED heat dissipation. As for on / off control is not sufficient, many design engineers to use at the same time coordinated by the flash subsystem and the camera shutter system microcontroller running the algorithm. The recently introduced smart LED flash controller already has more efficient LED control. For example, earlier this year, ex-Pu Semiconductor (NXP) announced the UBA3001, the device LED flash drive is the first series of devices, in support of the entire voltage range up to 90 percent efficiency level, to a single high-brightness LED provide up to 1 A band to support the current high-resolution camera phone. The new IC also provides for the flashlight mode and camera / video mode of the complete control of current settings.

Save space

Of course, PCB footprint of the space for space-constrained portable applications is always very precious.

May, Micrel announced the embedded camera for the boost converter based on the flash drive MIC2298, the device has more than 2 million pixels of resolution, for two series LED provide 1 A of current. The device is 3 ~ 3 mm MLF package, only need a compact 2 uH sensors and small ceramic capacitors.

Other manufacturers are through to a wider range of lighting functions into devices to help design engineers in space-saving footprint of the board at the same time reduce the number of components and reduce costs. For the phone's embedded in the first half of the LCD and camera module space-constrained candy bar phones, folding phones or slide phone, Maxim (Maxim) recently released a series of WLED driver of the mini-series in the 4 กม 4mm Package by adding two camera modules used to drive the programmable 200 mA LDO. Max 8645X and 8645 Y scores of charge pump used in the current maximum of 30 mA drive up to six WLED, and has five dimming accuracy. These devices can also at the highest under the current 200 mA drive two WLED, for use in camera flash applications.

Similarly, Advanced Analogic (AnalogicTech) also issued a charge pump based on the AAT2846, the device will be six backlight drivers, two flash drives and two General LDO and two independent single digital interface integrated on a single IC. This allows design engineers to build a backlight to provide an independent control function and flash solutions.