參數(shù)資料
型號： LTC3878IGN#PBF
廠商： LINEAR TECHNOLOGY CORP
元件分類： 穩(wěn)壓器
英文描述： SWITCHING CONTROLLER, PDSO16
封裝： 0.150 INCH, LEAD FREE, PLASTIC, SSOP-16
文件頁數(shù)： 26/26頁
文件大?。?/td> 399K
代理商： LTC3878IGN#PBF
LTC3878
3878fa
operaTion
LTC1778Compatibility
TheLTC3878iscompatiblewiththeLTC1778inapplica-
tionswhichdonotusetheEXTVCCfunction.TheLTC3878
offersimprovedgatedriveandreduceddeadtime,which
allowshigherefficiencythantheLTC1778.OntheLTC1778
Pin9isEXTVCC,butontheLTC3878itisanoconnect.
Theothernotabledifferenceisthattheshutdownlatch-
offtimerisremoved.TheLTC3878shouldbeadropin,
pin-for-pinreplacementinmostapplicationsthatdonot
useEXTVCC.TheLTC3878shouldbetestedandverified
ineachapplicationwithoutassumingcompatibility.Con-
tactaLinearapplicationsexperttoansweranyquestions
regardingLTC3878/LTC1778compatibility.
MainControlLoop
TheLTC3878isavalleycurrentmodecontrollerICfor
useinDC/DCstep-downconverters.Innormalcontinu-
ousoperation,thetopMOSFETisturnedonforafixed
intervaldeterminedbyaone-shottimer,OST.Whenthe
topMOSFETisturnedoff,thebottomMOSFETisturned
onuntilthecurrentcomparator,ICMP,trips,restarting
theone-shottimerandinitiatingthenextcycle.Inductor
valleycurrentismeasuredbysensingthevoltagebetween
thePGNDandSWpinsusingthebottomMOSFETon-
resistance.ThevoltageontheITHpinsetsthecompara-
torthresholdcorrespondingtoinductorvalleycurrent.
TheerroramplifierEAadjuststhisvoltagebycomparing
thefeedbacksignalVFBfromtheoutputvoltagetothe
feedbackreferencevoltageVFBREF.Increasingtheload
currentcausesadropinthefeedbackvoltagerelative
to the reference. The EA senses the feedback voltage
dropandadjuststheITHvoltagehigheruntiltheaverage
inductorcurrentmatchestheloadcurrent.
WithDCcurrentloadslessthan1/2ofthepeak-to-peak
rippletheinductorcurrentcandroptozeroorbecome
negative.Indiscontinuousoperation,negativeinductor
currentisdetectedandpreventedbythecurrentreversal
comparator IREV, which shuts off MB. Both switches
remainoffwiththeoutputcapacitorsupplyingtheload
currentuntiltheEAmovestheITHvoltageabovethezero
currentlevel(0.8V)toinitiateanotherswitchingcycle.
WhentheFCB(forcedcontinuousbar)pinisbelowthe
internalFCBthresholdreference,VFCB,theregulatoris
forcedtooperateincontinuousmodebydisablingreversal
comparator,IREV,therebyallowingtheinductorcurrentto
becomenegative.
Thecontinuousmodeoperatingfrequencycanbedeter-
mined by dividing the calculated duty cycle, VOUT/VIN,
by the fixed on-time. The OST generates an on-time
proportional to the ideal duty cycle, thus holding the
frequencyapproximatelyconstantwithchangesinVIN.
Thenominalfrequencycanbeadjustedwithanexternal
resistor,RON.
Foldbackcurrentlimitingisprovidedtoprotectagainst
lowimpedanceshorts.Ifthecontrollerisincurrentlimit
andVOUTdropstoless50%ofregulation,thecurrentlimit
set-point“foldsback”toprogressivelylowervalues.To
recoverfromfoldbackcurrentlimit,theexcessiveloador
lowimpedanceshortneedstoberemoved.
PullingtheRUN/SSpinlowforcesthecontrollerintoits
shutdownstate,turningoffbothMTandMB.Releasing
thepinallowsaninternal1.2Acurrentsourcetocharge
upanexternalsoft-startcapacitor,CSS.WhentheRUN/
SSpinislessthan0.7V,thedeviceisinthelowpower
shutdownconditionwithanominalbiascurrentof18A.
WhenRUN/SSisgreaterthan0.7Vandlessthan1.5V,
INTVCCandallinternalcircuitryareenabledwhileMTand
MBareforcedoff.Current-limitedsoft-startbeginswhen
RUN/SSexceeds1.5V.Normaloperationatfullcurrent
limitisachievedatapproximately3VonRUN/SS.Foldback
currentlimitisdefeatedduringsoft-start.
相關(guān)PDF資料
PDF描述
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
LTC3879EMSE#PBF 功能描述:IC REG CTRLR BUCK PWM CM 16-MSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:96% 電源電壓:4 V ~ 36 V 降壓:無 升壓:是 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR)
LTC3879EMSE#TRPBF 功能描述:IC REG CTRLR BUCK PWM CM 16-MSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:96% 電源電壓:4 V ~ 36 V 降壓:無 升壓:是 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR)
LTC3879EUD#PBF 功能描述:IC REG CTRLR BUCK PWM CM 16-QFN RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:96% 電源電壓:4 V ~ 36 V 降壓:無 升壓:是 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR)
LTC3879EUD#TRPBF 功能描述:IC REG CTRLR BUCK PWM CM 16-QFN RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:96% 電源電壓:4 V ~ 36 V 降壓:無 升壓:是 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR)
LTC3879IMSE#PBF 功能描述:IC REG CTRLR BUCK PWM CM 16-MSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:96% 電源電壓:4 V ~ 36 V 降壓:無 升壓:是 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR)
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