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Linear公司的LT3791是同步的四開關(guān)升壓-降壓LED驅(qū)動控制器,可使VIN高于,低于或等于VOUT,效率高達(dá)98.5%,輸入電壓4.7V-60V,輸出電壓0-60V,LED電流精度±6%,真彩色PWM和模擬調(diào)光,每個IC輸入功率100W或大于100W,主要用于汽車前燈/行駛燈和通用照明.本文介紹了LT3791主要特性,方框圖,多種應(yīng)用電路以及演示板DC1666A主要特性,電路圖,材料清單和PCB元件布局圖,測試電路圖. The LT®3791 is a synchronous 4-switch buck-boost LED driver controller. The controller can regulate LED current up to 52V of LED string with input voltages above, below, or equal to the output voltage. The constant-frequency, forced-continuous current mode architecture allows its frequency to be adjusted or synchronized from 200kHz to 700kHz. No top MOSFET refresh switching cycle is needed in buck or boost operation. With 60V input, 60V output capability and seamless transitions between operating regions, the LT3791 is ideal for LED driver applications in automotive, industrial, and even battery-powered systems. The LT3791 provides input current monitor, LED current monitor, and open or shorted LED fault condition, during which the LT3791 either restarts or latches off. LT3791主要特性: 4-Switch Single Inductor Architecture Allows VIN Above, Below or Equal to VOUT Synchronous Switching: Up to 98.5% Efficiency Wide VIN Range: 4.7V to 60V Wide VOUT Range: 0V to 60V (52V LED) ±6% LED Current Accuracy: 0V ≤ VLED < 52V True Color PWM™ and Analog Dimming LED and Input Current Regulation with Current Monitor Outputs No Top MOSFET Refresh in Buck or Boost VOUT Disconnected From VIN During Shutdown Open or Shorted LED Fault Protection Capable of 100W or Greater per IC 38-Lead TSSOP with Exposed Pad LT3791應(yīng)用: Automotive Head Lamps/Running Lamps General Purpose Lighting 
圖1.LT3791方框圖
圖2.LT3791效率98% 50W(25V2A)升-降壓LED驅(qū)動電路圖
圖3.LT3791效率98.5% 100W(33.3V3A)升-降壓LED驅(qū)動電路圖 演示板DC1666A Demonstration circuit DC1666A is a synchronous fourswitch buck-boost LED driver controller. It accepts an input voltage from 4.7V to 60V, and drives up to 25V of LEDs at 2A. DC1666A features both PWM and analog dimming of the LED string. It has an OPENLED flag that indicates when the LED string has been removed and it has a SHORTLED flag that indicates that the output has been shorted to GND. In both cases, the IC remains in control and well protected. DC1666A features very high efficiency at 300kHz switching frequency and continuous conduction mode (CCM). The synchronous four-switch topology both steps up and steps down voltage while regulating up to 50W of constant LED output current at efficiencies up to 98%. The circuit can be altered for applications requiring over 100W of LEDs. An optional SYNC terminal is provided for synchronizing to an external clock and CLKOUT terminal provides asource to sync another converter to the internal clock of the LT®3791. Three sense resistors provide constant output current control and monitoring, peak switch current control, and DC input current limit and monitoring. The ISMON and IVINMON outputs tell the user how much current is flowing through the output and input sense resistors. Small ceramic input and output capacitors are used to save space and cost. The open LED overvoltage protection uses the ICs constant voltage regulation loop to limit the output to approximately 28.3V if the LED string is opened. For low input voltage operation, the CTRL pin voltage is reduced as the input voltage drops below 6.5V, reducing LED brightness and restraining the peak switch currents in order to limit inductor and switch size. UVLO turns the LEDs off when VIN drops below 4.7V. When input rises above 57.6V, overvoltage lockout turns the switches off to protect them and they turn back on when VIN drops below 56.2V. DC1666A PWM dimming is simple. The PWM dimming MOSFET turns the LED string on and off with an input to the PWM dimming terminal. For the highest PWM dimming ratio, it is recommended to use 100Hz as a PWM dimming frequency. Information regarding PWM dimming ratios and performance can be found in the Applications Information section of the LT3791 data sheet. Analog dimming is also simple with a simple voltage source on the CTRL terminal. Modifications can be made to DC1666A in order to convert the board to higher or lower power or from an LED driver to a constant voltage regulator or battery charger. Please consult the factory or the LT3791 data sheet for details. The LT3791 data sheet gives a complete description of the part, operation and applications information. The data sheet must be read in conjunction with this demo manual for demonstration circuit DC1666A. The LT3791 is assembled in a 38-lead plastic TSSOP package with a thermally enhanced ground pad. Proper board layout is essential for maximum thermal performance. See the Layout Considerations section in the data sheet.
圖4.演示板DC1666A電路圖 演示板DC1666A材料清單(BOM):
圖5.演示板DC1666A測試電路圖 詳情請見: 
3791fa[1].pdf
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dc1666af[1].pdf
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來源：網(wǎng)絡(luò) |
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LT3791：升降壓100W LED驅(qū)動方案 Linear公司的LT3791是同步的四開關(guān)升壓-降壓LED驅(qū)動控制器，可使VIN高于、低于或等于VOUT，效率高達(dá)98.5%，輸入電壓4.7V~60V，輸出電壓0V~60V，LED電流精度±6%，真彩色PWM和模擬調(diào)光，每個IC輸入功率100W或大于100W。主要用于汽車前燈/行駛燈和通用照明。 其連續(xù)恒定頻率和強(qiáng)制恒定電流模式架構(gòu)，使其可以進(jìn)行調(diào)整，或同步200kHz~700kHz的頻率。在降壓或升壓操作時(shí)無需頂部MOSFET開關(guān)循環(huán)周期。該器件為60V輸入，60V輸出。和工作區(qū)域之間的無縫轉(zhuǎn)換，使LT3791成為LED驅(qū)動器在汽車、工業(yè)、電池供電系統(tǒng)的較理想選擇。 LT3791在重新啟動或閉鎖時(shí)，具有輸入電流監(jiān)控器，LED電流監(jiān)控器，以及LED開路或短路保障。
圖1 LT3791方框圖 LT3791主要特性 • 4開關(guān)單電感器架構(gòu)允許VIN高于，低于或等于VOUT • 同步切換：效率高達(dá)98.5％ • 4.7V~60V的寬VIN范圍： • 寬VOUT范圍：0V~60V（52V LED） • ±6％的LED電流精度：0V≤VLED<52V • True Color PWM和模擬調(diào)光 • LED電流監(jiān)視器輸出和輸入電流調(diào)節(jié) • 在降壓或升壓時(shí)無Top MOSFET刷新 • 在關(guān)機(jī)時(shí)，VOUT與 VIN斷開 • 開路或短路LED故障保護(hù) • 每IC 100W或更高的 • 帶裸焊盤的38引腳TSSOP LT3791應(yīng)用 • 汽車頭燈/行車燈 • 通用照明
圖2 LT3791效率98% 50W(25V2A)升-降壓LED驅(qū)動電路圖
圖3 LT3791效率98.5% 100W(33.3V3A)升-降壓LED驅(qū)動電路圖
圖4 DC1666A演示板電路圖 演示板DC1666A DC1666A演示電路是一個同步四開關(guān)降壓-升壓型LED驅(qū)動器控制器。它的輸入電壓為4.7V~60V，最高驅(qū)動2A、25V的LED。 DC1666A具有LED串的PWM和模擬調(diào)光功能。當(dāng)LED串被移動時(shí)，它的OPENLED標(biāo)志顯示；當(dāng)輸出短路到GND時(shí)，它的SHORTLED標(biāo)志顯示。在這兩種情況下，該IC保持控制，并有良好的保護(hù)。 DC1666A具有非常高的效率，其開關(guān)頻率為300kHz，并具有連續(xù)導(dǎo)通模式（CCM）。其同步四開關(guān)拓?fù)浣Y(jié)構(gòu)，在調(diào)節(jié)50W恒定LED輸出電流時(shí)（升壓和降壓），效率高達(dá)98％。該電路可以變化，用于超過100W的LED的應(yīng)用。一個可選的SYNC端子，用于同步一個外部時(shí)鐘和CLKOUT終端，并提供了另一個轉(zhuǎn)換器和內(nèi)部時(shí)鐘（LT3791）的同步資源。三個檢測電阻器提供了恒定的輸出電流控制和監(jiān)測、峰值開關(guān)電流控制和DC輸入電流限制和監(jiān)控。其ISMON和IVINMON輸出可以告訴用戶有多少電流流經(jīng)輸出和輸入的感測電阻。小陶瓷輸入和輸出電容器，以節(jié)省空間和成本。 LED開路過壓保護(hù)采用了IC恒定電壓調(diào)節(jié)環(huán)路，以限制輸出（大約28.3V，如LED串被打開）。對于低輸入電壓操作，當(dāng)輸入電壓低于6.5V時(shí)，CTRL引腳電壓被降低，并降低了LED的亮度和限制峰值開關(guān)電流，以限制電感和開關(guān)的大小。 當(dāng)VIN降至低于4.7V時(shí)，UVLO將LED關(guān)閉。當(dāng)輸入上升到高于57.6V時(shí)，過壓閉鎖功能將開關(guān)關(guān)閉作為保護(hù)，當(dāng)VIN降至56.2V時(shí)，重新開啟。 DC1666A PWM調(diào)光則很簡單，PWM調(diào)光MOSFET利用PWM調(diào)光終端的輸入來導(dǎo)通和關(guān)閉LED串。對于最高的PWM調(diào)光比，建議使用100Hz作為PWM調(diào)光頻率。對于PWM調(diào)光比和性能的信息，可以參見應(yīng)用信息部分的LT3791數(shù)據(jù)表。模擬調(diào)光也很簡單，采用一個簡單的CTRL終端電壓源。 DC1666A可以作出修改，以轉(zhuǎn)換該板到更高或更低的功率，或者以一個LED驅(qū)動器到一個恒定的電壓調(diào)節(jié)器或電池充電器。 LT3791數(shù)據(jù)表給出了一個完整的，操作和應(yīng)用信息的描述。數(shù)據(jù)表必須和使用手冊一并閱讀，以了解DC1666A電路。LT3791組裝在一個38引腳塑料TSSOP封裝里，并具有耐熱增強(qiáng)型地墊。正確的電路板布局對熱性能是必不可少的。 （中電網(wǎng)、《世界電子元器件》） |
