LED被稱為第四代照明光源或綠色光源，具有節(jié)能、環(huán)保、壽命長、體積小等特點，可以廣泛應(yīng)用于各種指示、顯示、裝飾、背光源、普通照明和城市夜景等領(lǐng)域。

　　LCD顯示屏中使用的LED驅(qū)動器有兩個要求。首先它們要能準(zhǔn)確控制和匹配每一個LED的亮度，這將限度地保持顯示屏背光的一致性；其次LED驅(qū)動器要能夠把輸入的電池電壓升高，這將保證在整個電池的使用周期內(nèi)能為LED提供足夠的驅(qū)動電壓，從而延長設(shè)備的使用時間。

　　基于電感的LED驅(qū)動器通常用于驅(qū)動串型連接的LED,此種結(jié)構(gòu)本身就能夠提供一致的匹配。它們還能夠提供可變和優(yōu)化的電壓升高比例，因此具有非常高的電源轉(zhuǎn)換效率。然而，由于外部元件的尺寸和成本，以及討厭的電磁干擾（EMI），基于電感的LED驅(qū)動器方案具有明顯的缺陷。體積龐大的儲能電感限制了這種方案在細長和低外觀的小型掌上設(shè)備中的應(yīng)用。另一方面，電荷泵型LED驅(qū)動器則提供了一個非常好的解決方案，其外部電路只需使用極小的電容即可。這使之成為進一步推動消費增長的更小更薄的便攜式設(shè)備的理想選擇

　　NS公司的LM3492是兩路單獨調(diào)光LED驅(qū)動器" title="LED驅(qū)動器">LED驅(qū)動器">LED驅(qū)動器，集成了升壓轉(zhuǎn)換器和快速電流穩(wěn)壓器?？删幊?a target="_blank">開關(guān)頻率從200 kHz到1 MHz,輸入電壓4.5V-65V,可編程LED電流從50 mA 到 200 mA,調(diào)光電壓達65V,總功率可達15W,主要應(yīng)用在超高對比度6.5"-10"難關(guān)LCD顯示屏背光以及汽車或航海GPS顯示器。本文介紹了LM3492主要特性， 簡化功能方框圖， 典型應(yīng)用電路圖以及LM3492評估板參考設(shè)計電路圖和評估板材料清單（BOM），PCB元件布局圖。

　　LM3492: Two-Channel Inpidual Dimmable LED Driver with Boost Converter and Fast Current Regulator

　　The LM3492 integrates a boost converter and a two-channel current regulator to implement a high efficient and cost effective LED driver for driving two inpidually dimmable LED strings with a maximum power of 15W and an output voltage of up to 65V. The boost converter employs a proprietary Projected- On-Time control method to give a fast transient response with no compensation required, and a nearly constant switching frequency programmable from 200 kHz to 1 MHz.

　　The application circuit is stable with ceramic capacitors and produces no audible noise on dimming. The programmable peak current limit and soft-start features reduce current surges at startup, and an integrated 190 mΩ， 3.9A N-Channel MOSFET switch minimizes the solution size. The fast slew rate current regulator allows high frequency and narrow pulse width dimming signals to achieve a very high contrast ratio of 1000:1 at a dimming frequency of more than 3 kHz. The LED current is programmable from 50 mA to 200 mA by a single resistor.

　　To maximize the efficiency, Dynamic Headroom Control （DHC） automatically adjusts the output voltage to a minimum. DHC also facilitates a single BOM for different number of LED in a string, which is required for backlight panels of different size, thereby reducing overall development time and cost.

　　The LM3492 comes with a versatile COMM pin which serves as a bi-directional I/O pin interfacing with an external MCU for the following functions: power-good, over-temperature, IOUT over- and under-voltage indications, switching frequency tuning, and channel 1 disabling. Other supervisory functions of the LM3492 include precise enable, VCC under-voltage lockout, current regulator over-power protection, and thermal shutdown protection. The LM3492 is available in the thermally enhanced eTSSOP-20 package.

　　LM3492主要特性：

　　Boost Converter:

　　■ Very wide input voltage ranged from 4.5V-65V

　　■ Programmable soft-start

　　■ No loop compensation required

　　■ Stable with ceramic and other low ESR capacitors with no audible noise

　　■ Nearly constant switching frequency programmable from 200 kHz to 1 MHz

　　Current Regulators:

　　■ Programmable LED current from 50 mA to 200 mA

　　■ 1000:1 contrast ratio at a dimming frequency of more than 3 kHz, minimum LED current pulse width is 300 ns

　　■ Two inpidual dimmable LED strings up to 65V, total 15W （typically 28 LEDs @ 150 mA）

　　■ Dynamic Headroom Control maximizes efficiency

　　■ Over-Power protection

　　■ ±3% current accuracy

　　Supervisory Functions:

　　■ Precision enable

　　■ COMM I/O pin for diagnostic and commands

　　■ Thermal shutdown protection

　　■ Thermally enhanced eTSSOP-20 package

　　LM3492應(yīng)用：

　　■ Ultra-high contrast ratio 6.5"-10" LCD display backlight up to 28 LEDs

　　■ Automotive or marine GPS display

　　圖1.LM3492簡化功能方框圖

　　圖2.LM3492典型應(yīng)用電路圖

　　LM3492評估板參考設(shè)計

　　LM3492 Evaluation Board Reference Design

　　The LM3492 integrates a boost converter and a two-channel current regulator to implement a high efficient and cost effective LED driver for driving two inpidually dimmable LED strings with a maximum power of 15W and an output voltage of up to 65V. The boost converter employs a proprietary Projected- On-Time control method to give a fast transient response with no compensation required, and a nearly constant switching frequency programmable from 200 kHz to 1 MHz.

　　The application circuit is stable with ceramic capacitors and produces no audible noise on dimming. The programmable peak current limit and soft-start features reduce current surges at startup, and an integrated 190 mΩ， 3.9A N-Channel MOSFET switch minimizes the solution size. The fast slew rate current regulator allows high frequency and narrow pulse width dimming signals to achieve a very high contrast ratio of 1000:1 at a dimming frequency of more than 3 kHz. The LED current is programmable from 50 mA to 200 mA by a single resistor.

　　To maximize the efficiency, Dynamic Headroom Control （DHC） automatically adjusts the output voltage to a minimum. DHC also facilitates a single BOM for different number of LED in a string, which is required for backlight panels of different size, thereby reducing overall development time and cost. The LM3492 comes with a versatile COMM pin which serves as a bi-directional I/O pin interfacing with an external MCU for the following functions: power-good, over-temperature, IOUT over- and under-voltage indications, switching frequency tuning, and channel 1 disabling. Other supervisory functions of the LM3492 include precise enable, VCC under-voltage lockout, current regulator Over-Power protection, and thermal shutdown protection. The LM3492 is available in the thermally enhanced eTSSOP-20 package.

　　This application note details the design of a LM3492 evaluation board which drives 2 LED strings, each of which consists of 10 LEDs running at 150 mA and the forward voltage of each LED is typically 3.8V. The input voltage is from 9V to 16V. The evaluation board schematic, PCB layout, Bill of Materials, and circuit design descriptions are shown. Typical performance and operating waveforms are also provided for reference.

　　圖3.LM3492評估板電路圖

　　評估板材料清單（BOM）：

　　圖4.評估板布局圖（頂層）