With the color LCD increasingly wide range of applications in handheld devices, the demand for compact and inexpensive white backlight, and more and more widely. Traditional program uses a cold cathode fluorescent lamp (CCFL) and electroluminescent (EL) panels, but these circuits for the current hand-held consumer products to large size, expensive, complex and other institutions of higher. At present, the recent development of LED technology has produced a white light LED. White LED lights and mass
Ship compared to the backlight has many advantages, including small size, low cost, low complexity and high reliability.
Today, a new generation of multi-functional cellular phone has been widely used in the domestic market. A new generation of mobile phones is not only compact size, and integration of more functions, such as PDA functions, to close / e-mail, text messaging services, as well as browse the Internet letter in a large size, rich colors on the monitor. Some mobile phone models
Also includes a frequency modulation (FM) radio. MP3 players, and even higher resolution digital cameras.
Whatever its function, the consumers, and always look forward to providing long-lasting battery life in handheld devices without increasing the size of the case. That is, not only in a small receiver with more features at the same time consume less power. Such a power management design is extremely demanding requirements. In response to the Peach war, manufacturers must address the following topics:
Power Manager IC (PMIC) on the basis of further deepen and broaden the application of trendy white LED technology and devices, to complete a new handheld or mobile phone supporting the best choice. This article presents a white LED trendy technology and devices to be introduced.
2, the white LED lamp is a new technology program
2.1 compact non-inductive boost circuit MAX1759-regulation white bias current
Typical of the white LED forward voltage of about 3.5V ± 10%, only for the device to provide a positive bias to white light. Need to step-up circuit when the white light LED forward voltage than the battery voltage, the traditional solution is to use the boost circuit, through the ballast resistor provides bias for the LED, this program there are two defects: First, the white LED more the wide range of forward voltage variations can cause large changes in bias current, the brightness deviation; Secondly, the traditional step-up program have a DC path between input and output (even in the off state), so that does not work LED unnecessary consumption of battery current.
To overcome the above drawbacks, a new non-inductive boost circuit MAXl759 (regulator type buck / boost charge pump) is a compact solution, shown in Figure 1 circuit. The regulator type l / step-down charge pump (uMAX) package of small size, can provide 100mA output current. In accordance with the configuration in Figure 1, can be directly provide a stable bias current of white LED bias multiple parallel LED with good brightness distribution. MAXl759 circuit shutdown there is no DC path between input and output, users can take advantage of the input control backlight pass, breaking. The circuit also with a power-good (POK) output, whether it has been prepared to inform the microprocessor backlight good.