原标题：Semtech SC442高效120个白光LED驱动方案

　　Semtech 公司的SC442是10路高效120个白光LED驱动器，输入电压4.5V-21V，高效的升压转换器可使输出电压高达42V，非常适合中到大型LCD显示屏。电流沉可编程，每路高达30mA，路间的电流匹配在+/-1%，集成了3A开关，效率高达91%，可灵活进行LED配置，高达50kHz调光频率，大于500:1调光范围，开关频率500kHz - 1MHz，主要用在汽车LCD背光，台式监视器，笔记本电脑和手提TV。本文介绍了SC442主要特性和典型应用电路。

　　SC442：10-Channel, Integrated, High Efficiency 120 White LED Driver

　　The SC442 is a 10-channel, high efficiency integrated step-up (boost) driver IC capable of powering up to 120 WLEDs. The device has a wide input voltage of 4.5V to 21V with no internal regulator or bypass capacitor required. The wide input range, up to 42V output voltage and flexible implementation make it the ideal LED backlight driver solution for medium to large LCD displays. The current sink channels are programmed with an external resistor up to 30mA each.

　　Channel-channel current matching is +/-1% . The device disables open or shorted LEDs by disabling only the affected LED channel; thus increasing LCD panel life. Channel-channel LED mismatch voltage is accomodated by adjusting the SCPSET resistor. The current sink channels may be operated in parallel for increased LED current. Unused channels are be disabled by connecting the pin to the input voltage.

　　Losses in the switching device and current sinks are minimized across the operating range; yielding >90% efficiency and excel­lent battery life for portable systems.

　　The device accepts PWM dimming up to 50kHz. Maximum dim­ming range is greater than 500:1 with excellent linearity for opti­mum PWM dimming characteristics. The high frequency dimming capability (>20kHz) eliminates audio emissions and allows small ceramic output capacitors.

　　Switching frequency is programmable from 200kHz to 1MHz; allowing efficiency versus L/C sizing tradeoffs across the input/output voltage range. Alternatively, the SYNC pin allows the designer to synchronize the switching frequency to an external system clock and, if necessary, a parallel SC442 device - eliminating potential system intermodulation and interference problems.

　　Over-temperature shutdown protects the IC from over-heating under abnormal conditions. The device is available in a small 4mmx4mm MLPQ-28 pin package with 0.6mm maximum height and is fully WEEE and RoHS compliant.

　　SC442主要特性：

　　Wide input voltage range from 4.5V to 21V

　　42V maximum operating output voltage

　　Programmable LED current up to 30mA per string

　　+/- 1% current matching

　　Integrated 3A switch

　　Low current sink voltage

　　Up to 91% efficiency

　　Flexible LED configurations

　　Mismatched LED channels

　　Disable individual channel(s)

　　Parallel channels for high LED current

　　PWM dimming capability

　　Up to 50kHz dimming frequency

　　>500:1 dimming range

　　Switching frequency: 500kHz - 1MHz

　　Parallel device operation with Sync Pin

　　Protection features:

　　Adjustable OVP

　　Cycle-by-cycle current limit

　　LED short channel with disable /Open channnel

　　Over-Temperature protection

　　MLPQ-28 lead-free package (WEEE and RoHS compliant), 4×4mm × 0.6mm

　　SC442应用：

　　Automotive LCD Backlighting

　　Desktop monitors

　　Notebook PCs

　　Portable TVs

　　图1。SC442典型应用电路