一個(gè)靈活的LED驅(qū)動(dòng)汽車照明應(yīng)用集成電路設(shè)計(jì)和實(shí)驗(yàn)特征 畢業(yè)設(shè)計(jì)文獻(xiàn)翻譯

1、畢業(yè)設(shè)計(jì)文獻(xiàn)翻譯院系： 電子電氣工程學(xué)院 學(xué) 號(hào)： 姓 名： 吳驍奕 指導(dǎo)教師： 曾國(guó)輝 完成時(shí)間： 2013/2/15 文獻(xiàn)翻譯 吳驍奕A Flexible LED Driver for Automotive Lighting Applications: IC Design and Experimental Characterization一個(gè)靈活的LED驅(qū)動(dòng)汽車照明應(yīng)用:集成電路設(shè)計(jì)和實(shí)驗(yàn)特征AbstractThis letter presents a smart driver for LEDs, particularly摘要：這文章提出了一個(gè)智能驅(qū)動(dòng)發(fā)光二極管，for automotiv

2、e lighting applications, which avoid ringing尤其是用于避免振蕩和超調(diào)現(xiàn)象的汽車照明應(yīng)用上，and overshoot phenomena. To this aim, advanced Soft Start and為了這個(gè)目的，在芯片上集成了優(yōu)化軟啟動(dòng)和電流升降控制技術(shù)。Current Slope Control techniques are integrated on-chip. This letter這篇文章討論了設(shè)計(jì)于集合于高電壓的互補(bǔ)金屬氧化半導(dǎo)體上的驅(qū)動(dòng)技術(shù)，discusses the driver design integrating in

3、 high voltage CMOStechnology, the digital circuitry for programming and electronic用于編程和電子控制單元連接的數(shù)字電路以及功率元件提高到10瓦特。control units interfacing, and the power devices up to 10W. Experimental同時(shí)也展示了不同功率等級(jí)使用的發(fā)光二極管和與不同類型的連接時(shí)的實(shí)驗(yàn)特征。characterizations with LEDs of different power levels andwith different types

4、of connections are showed. The smart driver這個(gè)智能的驅(qū)動(dòng)適用于可調(diào)節(jié)的溫度和電壓需求。sustains automotive temperature and voltage requirements; moreover此外，它有很高的功率效率，它是可編程的，還可以配置用于線性的調(diào)節(jié)器。it has high power efficiency, it is programmable, and can beconfigured to work as a linear regulator (for low current LEDs) orin switch

5、 mode (for higher power LEDs).（用于弱電流發(fā)光二極管）或轉(zhuǎn)換模式（用于高功率發(fā)光二極管）IndexTermsAutomotive electronics, high voltage (HV)CMOS,integrated circuit (IC), LED driver.關(guān)鍵詞汽車用電子設(shè)備，高電壓互補(bǔ)金屬氧化物半導(dǎo)體，集成電路LED驅(qū)動(dòng)I. INTRODUCTION1：介紹IN the last few years LED technology experienced a very fast在過(guò)去的幾年中，發(fā)光二極管技術(shù)在汽車照明應(yīng)用中替代普通燈泡經(jīng)歷了一個(gè)非常

6、快速的進(jìn)步時(shí)代，and important growth, superseding the bulb technology inautomotive lighting applications 1. To achieve the harsh requirementof CO2 emission and reduce the fuel consumption,car manufacturer must reduce the total power consumption. The為了實(shí)現(xiàn)了嚴(yán)格的二氧化碳排放要求和降低了燃料的消耗,汽車制造商必須減少總的功率消耗。adoption of LEDs

7、in place of bulbs permits to have about fivetimes less power consumption at equal output lighting intensity.采用發(fā)光二極管代替燈泡在同等輸出功率照明強(qiáng)度下?lián)p耗將降低五倍。LEDs have reached quality and reliability factors that permittheir use in automotive harsh environment and in addition發(fā)光二極管已達(dá)到質(zhì)量和可靠性因素,可保證他們可使用在汽車的嚴(yán)酷環(huán)境下并且他們的成本是降

8、低的。their cost is decreasing. However, LEDs are pretty difficult to事實(shí)上，發(fā)光二極管是很難驅(qū)動(dòng)，因此相比較普通燈泡，發(fā)光二極管驅(qū)動(dòng)要求更多的技巧和控制功能。drive and therefore LED-drivers require many tricks and controlfunctions compared to bulb drivers. Moreover, automotive而且，汽車應(yīng)用程序需要緊湊和低成本的解決方案,靈活足夠的數(shù)字電子控制單元界面， applications require compact a

9、nd low-cost solutions, flexibleenough to be interfaced to digital electronic control units (ECU)and to cope with different wiring configurations and relevant同時(shí)需要應(yīng)付不同的布線配置和相關(guān)拓展。parasitics 2. Automotive lighting systems should be also robust汽車照明系統(tǒng)也應(yīng)該對(duì)電磁干擾(EMI)和超溫、過(guò)流以及過(guò)電壓現(xiàn)象有應(yīng)變能力。with respect to electro

10、magnetic interference (EMI) andto overtemperature, overcurrent, and overvoltage phenomena,such as those due to ringing effects generated by resonance of例如那些由于激振效應(yīng)所產(chǎn)生的共振的線電感和連接器電容。wire inductance and connector capacitance. Usually, in car environment通常,在汽車環(huán)境中，幾米長(zhǎng)電線使用,就會(huì)生成強(qiáng)烈振蕩。few meters long wires ar

11、e used, generating dumpedoscillations. Such oscillations and the associated overcurrentand overvoltage levels reduce the LED life time and its efficiency這種振蕩和與之相關(guān)的過(guò)電流和過(guò)電壓會(huì)降低發(fā)光二極管壽命及其效率。3. To avoid or limit these effects the LED cannot bedriven by a mechanical relay but a smart driver is required toc

12、ontrol the slope of the LED current during transient, keeping it為了避免或限制這些影響發(fā)光二極管不能由一個(gè)機(jī)械繼電器控制但智能的驅(qū)動(dòng)被要求需要在瞬態(tài)控制LED電流的斜率，以保持它在電線的特征頻率以下。below the characteristic frequency of the wire. A compact andefficient LED driver is needed, overcoming the above issues andfeaturing a high flexibility to face differe

13、nt LED power levels,一個(gè)緊湊和高效的LED驅(qū)動(dòng)程序是必要的,是為了克服上述問(wèn)題和具有高靈活性，去面對(duì)不同的發(fā)光二極管功率級(jí)別，連接拓?fù)浜碗娋€寄生。connections topology, and wiring parasitics. Hereafter, Section此后，在第二部分，分析了振蕩和電磁干擾在放光二極管驅(qū)動(dòng)中的影響。II analyzes ringing and EMI problems in LED driving. SectionIII presents the design of the new LED smart driver focusing o

14、n第三部分介紹了一款新設(shè)計(jì)的智能發(fā)光二極管驅(qū)動(dòng)的顯著特征。its distinguishing features. Section IV presents its experimental第四部分介紹了發(fā)光二極管在不同功率等級(jí)下的實(shí)驗(yàn)特征，從幾十毫瓦特characterization with LEDs of different power levels, from tensof milliwatts to several watts, used stand-alone, or connected in到幾瓦特在獨(dú)立或幾個(gè)連接下的狀態(tài)。strings. Temperature and volt

15、age range operating conditions are溫度和電壓等級(jí)的工作條件也被測(cè)量判斷。also measured. Conclusions are drawn in Section V.第五部分將引出結(jié)論。II. RINGING AND EMI PROBLEMS IN LED DRIVING二.振蕩和電磁干擾在發(fā)光二極管驅(qū)動(dòng)中的影響At state-of-the-art LED, driving is implemented using lowdropout linear regulators, which are limited to LEDs of few tensof

16、 milliamperes, or more power-efficient switching solutions athigher current levels 在最開(kāi)始的LED,開(kāi)車是使用低輸出線性穩(wěn)壓器,僅限于幾十毫安級(jí)的發(fā)光二極管,或更省電轉(zhuǎn)換解決方案用在更高的電流水平。310. However, a compact solution integrating然而,一個(gè)緊湊的集成解決方案在一個(gè)單芯片數(shù)字ECU接口,on a single chip a digital ECU interface, a low-powerconfigurable logic core, a power p

17、art able to work in linear modeor switching one, as well as advanced techniques such as SoftStart and Current Slope Control, has not been proposed yet in一個(gè)低功耗可配置的邏輯核心,電源部分能夠工作在線性模式或轉(zhuǎn)換它,以及先進(jìn)的技術(shù),如軟開(kāi)始和電流升降調(diào)節(jié)，還沒(méi)有在文獻(xiàn)中被提出。the literature. The main difficulties in the design of a universal設(shè)計(jì)一個(gè)足夠的靈活的發(fā)光二極管驅(qū)動(dòng)應(yīng)

18、用在不同的接線配置最大的難題是振蕩和電磁干擾問(wèn)題。LED driver, flexible enough to be applied to different wiringconfigurations, are the ringing and EMI issues. These problems這些問(wèn)題取決于環(huán)境因素和寄生組件，這些因素很難去假設(shè)和模仿。depend on environmental and parasitic components that are difficultto predict and simulate.While bulbs are easily modeled

19、as而電燈泡卻很容易模仿因?yàn)樗芯€性的正溫度系數(shù)并且寄生成分對(duì)它的影響比較小。linear positive temperature coefficient (PTC) resistors, and areless sensitive to parasitic components, a LED is a special diode發(fā)光二極管是一種特殊的二極管，它滿足肖克利指數(shù)電流-電壓法。and follows the Shockley exponential IV law. A very smallfluctuation on the voltage across the LED can

20、generate a very一個(gè)很小的電壓起伏通過(guò)發(fā)光二極管可能引起一個(gè)很大的電流變化影響。high variation on its current affecting, as proved in 3, both efficiency經(jīng)證明，效率和照明設(shè)備的壽命都將被影響。and life time and creating lighting disturbs. This behavior如果發(fā)光二極管沒(méi)有恰當(dāng)?shù)谋或?qū)動(dòng)的話這個(gè)行為會(huì)導(dǎo)致振蕩和高強(qiáng)度的電流尖脈沖。can generate ringing and high current spikes if the LED is not pr

21、operly driven. By the same token, a bulb-designed driver, as出于同樣的原因，燈泡的驅(qū)動(dòng)，正如10-12中說(shuō)的，不能被直接用于驅(qū)動(dòng)發(fā)光二極管。shown in 1012, cannot be directly used to drive efficientlyLEDs. This is particularly true when the LED and the driver are這一點(diǎn)是完全正確的當(dāng)發(fā)光二極管和驅(qū)動(dòng)在汽車連接中被幾米的電纜分割的時(shí)候。separated by a few meter cables as in auto

22、motive connections.In this case, the wiring parasitics can generate ringing and EMI.出于這個(gè)原因，電線的寄生將引起振蕩和電磁干擾。A comparison based on experimental measurements, between一個(gè)在二瓦特的燈泡和0.1瓦特的連著很短的線（大概10厘米長(zhǎng)）發(fā)光二極管的比較實(shí)驗(yàn)中顯示在圖1和圖2中。a 2-W bulb lamp and a 0.1-W LED turn-on transient with veryshort wire (about 10 cm lo

23、ng) and with very long wire (about3m long) is shown, respectively, in Figs. 1 and 2. A simplerelay is used as a switch to highlight the different behavior一個(gè)簡(jiǎn)單的繼電器被用來(lái)切換到這些負(fù)載不同的狀態(tài)。of those loads. Those pictures show the necessity of using a這些圖片展示了使用一個(gè)設(shè)計(jì)良好的LED驅(qū)動(dòng)從而避免寄生電路的重要性。well-designed driver for LED

24、s, to avoid unwanted effects dueto wiring parasitics. In fact, the behavior of the current in the事實(shí)上，燈泡的電流狀態(tài)不隨著線的長(zhǎng)度而變化。從圖1a圖2a可以看出bulb does not change significantly with the wire length seeFigs. 1(a) and 2(a) while the transient of the current in the而發(fā)光二極管的瞬間電流缺有顯著的差異。從圖1b和2b可以看出LED shows significan

25、t differences see Figs. 1(b) and 2(b). Toovercome this issue we propose a compact solution, integrating為了解決這個(gè)問(wèn)題我們計(jì)劃了一個(gè)簡(jiǎn)潔的方案：in 0.35-mHVCMOStechnology the digital circuitry for driverinterfacing/configuration and power devices up to 10W, with采用高壓CMOS技術(shù)數(shù)字電路的驅(qū)動(dòng)程序，接口/配置和功率設(shè)備提高到10 瓦特HV protection up to 5

26、5V. The LED driver can be interfaced to同時(shí)高壓保護(hù)提高到55伏特。LED驅(qū)動(dòng)可以被顯示到數(shù)字電子控制單元，digital ECU 1315 and is able to cope with different wiring從而它可以處理各種長(zhǎng)度的電線配置和寄生電路。configurations some meters long and their parasitics 2, and to使其適應(yīng)作為線性穩(wěn)壓器和開(kāi)關(guān)的表現(xiàn)，取決于編程的精度。adapt its behavior working as linear regulator or as a swi

27、tchingone, depending on a programmable threshold.III. FLEXIBLE LED DRIVER IC三. 靈活的發(fā)光二極管驅(qū)動(dòng)集成電路With respect to the bulb lamp driver shown in 11, 12 the關(guān)于指示燈驅(qū)動(dòng)器了，智能LED驅(qū)動(dòng)必須滿足嚴(yán)酷的汽車環(huán)境約束。smart LED driver needs to fulfill the same harsh automotive environmentconstraints, as well as more power demanding load

28、s,同時(shí)也要滿足更多的功率負(fù)載需求用于串聯(lián)和并聯(lián)配置下的發(fā)光二極管。as series and parallel configuration of LEDs. Low power LEDs,like those employed in the car dashboard, absorbing 3050mW,像那些30-50毫瓦的用于汽車儀表盤(pán)的低功率發(fā)光二極管，包括那些排列在一起的總功率到10瓦特的發(fā)光二極管或燈泡，能被提議的設(shè)計(jì)驅(qū)動(dòng)。as well as arrays of power LEDs or lamps up to 10W, can bedriven properly by the

29、 proposed design. 圖1.（a）燈泡（b）發(fā)光二極管 在沒(méi)有任何電流電壓控制的10厘米電纜下?tīng)顟B(tài)圖2 （a）燈泡（b）發(fā)光二極管 在沒(méi)有任何電流電壓控制3厘米電纜下?tīng)顟B(tài)圖3. 方案一允許的負(fù)載配置,加強(qiáng)了布線寄生現(xiàn)象,發(fā)光二極管,和串聯(lián)的電池中的開(kāi)關(guān)。圖4.LED驅(qū)動(dòng)集成電路的體系結(jié)構(gòu)和詳細(xì)電路The driving of LEDs has required the implementation of specific techniques to limit the undesired effects of wiring parasitics, 發(fā)光二極管的驅(qū)動(dòng)要求實(shí)施特定的技

30、術(shù)來(lái)限制布線寄生現(xiàn)象帶來(lái)的不良影響。such as ringing andconsequent overshoots and undershoots如振蕩和隨之引起的超調(diào)量和脈沖信號(hào)。.In Fig. 3, the scheme of the wiring parasitic and of a possible connection betweenthe driver and the load is shown: the output pin of the driver,在圖三中，該計(jì)劃的布線寄生和可能的在驅(qū)動(dòng)和負(fù)載的連接中顯示:輸出的驅(qū)動(dòng)程序，其功能可以用一個(gè)簡(jiǎn)單的開(kāi)關(guān)描述，是連接發(fā)光二極管

31、，并且和汽車的whose functionality can be represented by a simple switch tothe ground, is connected to a LED, in series with the car batteryand another switch, controlled by the user through a button or電池和另外一個(gè)開(kāi)關(guān)連接，而用戶通過(guò)一個(gè)按鈕或點(diǎn)火鑰匙來(lái)控制它。the ignition key. The basic scheme of the flexible LED driveris shown in Fi

32、g. 4, together with circuit details of the operational這個(gè)靈活的發(fā)光二極管驅(qū)動(dòng)基本方案以及電路詳細(xì)的步驟和跨導(dǎo)放大器塊如圖四所示。transconductance amplifier (OTA) block: the architecture這個(gè)設(shè)計(jì)基于一個(gè)is based on a voltage regulation loop inserted inside a linear loopproviding the current control capability.插入在一個(gè)線性循環(huán)的電壓調(diào)節(jié)回路以提供當(dāng)前的控制能力。The volta

33、ge regulationloop forces the output on a reference voltage, Vref , when 電壓調(diào)節(jié)回路控制輸出的是參考電壓當(dāng)?shù)蛪簻y(cè)主電源開(kāi)關(guān)串聯(lián)二極管以提供反極性的容量給裝置，是開(kāi)啟了。the low side main power switch (power MOS in Fig. 4), in series withthe Diode that provides reverse polarity capability to the device,is turn ON. The LED driver has been integrated

34、 as hard macrocellLED驅(qū)動(dòng)程序已經(jīng)被集成在一個(gè)復(fù)雜的大容量的電池汽車控制單元集成電路中in a complex automotive control unit IC, implemented inAustria micro systems (AMS) 0.35 m CMOS technology. Fig 5被用在AMS0.35UM的互補(bǔ)金屬氧化物半導(dǎo)體技術(shù)中。從圖5中可以看出，shows the layout and the photo of the whole control unit IC,布局和圖片的整個(gè)控制單元集成在電路中，使得發(fā)光二極管驅(qū)動(dòng)電子電路增強(qiáng)。high

35、lighting the LED driver circuit, and particularly the powerMOS and its protection diode in Fig. 4, which occupy most ofthe LED driver area.特別的在圖四中的MOS材料和二極管的保護(hù)，占絕了絕大部分的發(fā)光二極管驅(qū)動(dòng)電路。By regulating the output voltage on a reference level the stateof the load and of the power switch can be easily detected.

36、通過(guò)調(diào)節(jié)輸出電壓在一個(gè)參考電平狀態(tài)的負(fù)載和電源開(kāi)關(guān)可以很容易地被檢測(cè)到。When the LED is ON (user switch and power switch in Fig. 3當(dāng)發(fā)光二極管打開(kāi)，（用開(kāi)關(guān)或者圖3的電源開(kāi)關(guān)都可以使運(yùn)轉(zhuǎn)）both enabled), the regulation loop is activated and the output調(diào)節(jié)回路是激活的，輸出電壓是控制為參考電壓的。Vo is forced on the reference voltage, Vref . If the user switch同時(shí)強(qiáng)制發(fā)光二極管也關(guān)閉，如果關(guān)閉開(kāi)關(guān),因此發(fā)光二極管也

37、關(guān)閉is OFF, and hence also the LED is OFF, the output pin of thedriver is pulled down even when the power switch is OFF, by輸出引線驅(qū)動(dòng)被損壞甚至電源總開(kāi)關(guān)也關(guān)掉，意味著編的程序沒(méi)有應(yīng)變能力。means of a programmable resistive path to ground. That pathis highly resistive to limit to very low value the current flowingthrough the LED. Fin

38、ally, if the user switch is ON but the這條道路的高電阻是用來(lái)限制非常低的電流來(lái)通過(guò)發(fā)光二極管，如果用戶開(kāi)關(guān)打開(kāi)但電源開(kāi)關(guān)關(guān)閉，那么輸出電壓將強(qiáng)迫輸出為電源的額定電壓。power switch is forced OFF, then the output Vo is pulled up tothe battery voltage, Vbatt , and the LED is OFF since no noticeable發(fā)光二極管也將關(guān)閉直到?jīng)]有明顯的電流通過(guò)。current is flowing. Summarizing, depending on th

39、e statusof the switch devices in Fig. 3, the output voltage Vo can bepulled down to ground, or pulled up to Vbatt or forced to Vref .根據(jù)不同開(kāi)關(guān)設(shè)備的狀態(tài)，如圖3所示,輸出電壓可以接地,或者強(qiáng)迫為電源的額定電壓。A comparator can reveal the status of the driver and also potentialovervoltage conditions by comparing the output voltageto pro

40、per thresholds. Similarly overcurrent and overtemperature一個(gè)比較器可以顯示驅(qū)的狀態(tài)和通過(guò)比較輸出電壓合適的閾值看出潛在的過(guò)壓條件。phenomena can be detected by comparing the measured currentand temperature values (through an on-chip temperature sensor)with proper thresholds. All reference and threshold levels are同樣的過(guò)電流和超溫現(xiàn)象是可以探測(cè)到的測(cè)量的電流

41、和溫度的值(通過(guò)一個(gè)芯片上的溫度傳感器)和適當(dāng)?shù)拈撝当容^。internally generated by a digital-programmable band-gap unit.所有的引用和閾值水平是由內(nèi)部產(chǎn)生的數(shù)字通過(guò)可編程的帶隙裝置。The measurements shown in this letter are obtained with a Vref這篇文章中的測(cè)量值是通過(guò)額定電壓獲得，1.2伏特。of 1.2V. The detected driver and load status are used by theinternal logic as feedback signal

42、s to properly drive the powerMOS in Fig. 4, acting as linear regulator or ONOFF switch,檢測(cè)到的驅(qū)動(dòng)和負(fù)載狀態(tài)使用內(nèi)部邏輯作為反饋信號(hào)正確驅(qū)動(dòng)動(dòng)力在圖四中的金屬氧化物半導(dǎo)體,是作為線性調(diào)節(jié)器或開(kāi)關(guān)and implementing advanced Soft Start or Current Slope Control techniques.和實(shí)施先進(jìn)的軟啟動(dòng)或電流升降控制技術(shù)The working mode of the LED driver, as linear regulator orONOFF swit

43、ch, is determined by the user by proper configuringthe Current level Iref in Fig. 4. The MOSMA mirrors a small工作模式的LED驅(qū)動(dòng),線性調(diào)節(jié)器或通斷開(kāi)關(guān),是由用戶通過(guò)適當(dāng)?shù)呐渲迷趫D4按圖四的電流是水平。fraction of the power MOS output current and, through the HVand Low-Voltage (LV) current mirrors in Fig. 4, MOSMA反射小部分功率從MOS輸出電流,如圖四通過(guò)高壓和低壓(LV)電

44、流反射鏡鏡，compares it to the Iref current value (generated through on-chip band-gap circuit).比較其當(dāng)前值(通過(guò)芯片上的帶隙電路生成Iref)。The HV PMOS current mirror is connected to the outputvoltage, which is up to 12V, while the LV PMOS current mirroris connected to Vdd = 3.3V. The difference between Imir and高壓PMOS的電流反射連接

45、到輸出電壓提高到12伏特,而低壓PMOS電流反射連接到Vdd是3伏特。Iref drives the gate of MOS MB : if Imir is lower than Iref , thenImir和Iref之間的在MOS驅(qū)動(dòng)上的區(qū)別是：如果Imir低于Irel，那么MB是關(guān)閉的MB is OFF and the power MOS, driven by the OTA in Fig. 4,并且MOS的能量是由如圖四中的OTA驅(qū)動(dòng)的，通過(guò)線性的電流調(diào)節(jié)器。acts as a linear current regulator. Otherwise, MB is ON and the反

46、之，如果MB是打開(kāi)的而電流環(huán)路控制開(kāi)關(guān)關(guān)閉，那么MOS MB將會(huì)被強(qiáng)制關(guān)閉。current loop control switches to the OFF state the power MOS.The MOS MB can be forced back in OFF state, and hence the同時(shí)強(qiáng)制電源MOS起作用，如圖四用來(lái)進(jìn)行邏輯控制。powerMOS reactived, by the control logic in Fig. 4. The controllogic determines the times Ton and Toff when MB is OFF (

47、i.e.,這個(gè)控制邏輯決定什么時(shí)候開(kāi)什么時(shí)候關(guān)分別當(dāng)MB關(guān)掉的時(shí)候（MOS開(kāi)著）power MOS is ON) or MB is ON (i.e., power MOS is OFF), respectively.或者M(jìn)B開(kāi)著（MOS關(guān)閉）In this case, the driver is working in ONOFF switch因此，這個(gè)驅(qū)動(dòng)工作在關(guān)或開(kāi)的模式為了滿足控制邏輯不停的變換開(kāi)關(guān)。mode with duty cycle and frequency depending on the Ton andToff times set by the control logic.S

48、ummarizing, in linear regulator mode Iref is configured sothat the current loop control is activated only for output currentsof several amperes, much higher than the operating load currents總結(jié),在線性調(diào)節(jié)器模式Iref是如此配置的為了電流環(huán)路控制輸出電流只有安培。foreseen for this LED driver (see Section IV). In linear mode,遠(yuǎn)高于操作負(fù)載電流的L

49、ED驅(qū)動(dòng)程序(見(jiàn)第四部分)。在線性莫模型中，Iref acts as a protection threshold: if Imir is over Iref then MB isIref擔(dān)當(dāng)著一個(gè)保護(hù)的臨界值：當(dāng)Imir超過(guò)了Iref，那么MB會(huì)打開(kāi)，電源MOS會(huì)關(guān)閉。switched ON and the power MOS is switched OFF.In ON/OFF switching mode, Iref is configured at levels lower在開(kāi)/關(guān)模式下，Iref是按從低到高電流等級(jí)配置的。than normal operating currents:

50、the power MOS is no directlydriven by the OTA and the combined action of the current loopcontrol and of the control logic on the MOS MB determines theTon and Toff periods (and hence the switching duty cycle andfrequency) of the power MOS. To be noted that in switching電源MOS沒(méi)有直接被OTA和聯(lián)合作用的電流環(huán)路控制。同時(shí)控制邏輯

51、在MOS MB上決定了開(kāi)或者關(guān)的周期(因此切換工作周期和頻率)。mode Iref is not acting as the sole current limitation level; thedetection of overcurrent phenomena is carried out by the Over-I and Over-V detect block in Fig. 4. The described approach注意,在切換模式Iref不是作為唯一的電流限制水平;檢測(cè)過(guò)流現(xiàn)象是被運(yùn)用于過(guò)壓過(guò)流檢測(cè)塊,如圖4所示。allows to implement two functio

52、ns in the same LED driver IC atminimal hardware overhead: linear regulator mode, useful for所述方法可以實(shí)現(xiàn)兩個(gè)功能相同的LED驅(qū)動(dòng)集成電路在最小的硬件開(kāi)銷:線性穩(wěn)壓器，用于瞬間的變化和低電流低功率LED，當(dāng)電源效率不是問(wèn)題的時(shí)候。fast transient and low-current/low-power LEDs, where powerefficiency is not an issue; switch driving mode, useful for higher開(kāi)關(guān)驅(qū)動(dòng)方式，用于高電流和高功

53、率LED，當(dāng)電源效率是關(guān)鍵問(wèn)題所以current and higher power LEDs where the power efficiency is akey issue and therefore a switching regulator has to be preferredto a linear one.線性的開(kāi)關(guān)穩(wěn)壓器將被成為首選。The driving of a LED calls also for specific strategies toavoid the ringing phenomenon on the connecting wire withthe conseque

54、nt current overshoot. The Soft Start and Current發(fā)光二極管的驅(qū)動(dòng)也要求具體策略在連接線上避免振蕩現(xiàn)象與隨之產(chǎn)生的電流超調(diào)。Slope Control techniques, proposed by the authors in 12 forbulb lamp driving (low-power dashboard indicator), have beenimproved to maintain the same proper behavior also with arraysof LEDs and high luminosity up to

55、10W. The design has taken軟啟動(dòng)和電流斜率控制技術(shù),作者在12中提出的燈泡驅(qū)動(dòng)(低功耗儀表板指示器),被用來(lái)保持適當(dāng)?shù)臓顟B(tài)，同時(shí)也排列二極管把光度提高到10瓦特。into account the variability of parasitic capacitors and inductors,設(shè)計(jì)已經(jīng)考慮到可變性的寄生電容和電感,as well as of the load and all process-voltage-temperature (PVT)以及負(fù)載和所有過(guò)程電壓溫度(PVT)的部分。corners. As shown in Fig. 6, by swe

56、eping through different如圖六所示，通過(guò)不同的布線寄生現(xiàn)象和等效電阻對(duì)不同負(fù)載配置的發(fā)光二極管，values of the wiring parasitics and of the equivalent resistancefor different LED-based load configurations, the phase margin電壓調(diào)節(jié)回路的相位補(bǔ)角,如圖4所示，在一個(gè)相關(guān)的方式下變化。of the voltage regulation loop in Fig. 4 changes in a relevantway.As a consequence, the susceptibility to instability of the overall因此，circuit varies, along with the entity of the ringing, as illustrated不穩(wěn)定的磁感系數(shù)的整體電路的變化,隨著實(shí)體振蕩，在圖7中闡述的那樣。in Fig. 7. To deal with