Semtech SC442高效120个白光LED驱动方案
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摘要： 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。
Abstract：
Key words :
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
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
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