參數(shù)資料
型號： LTC3878IGN#TRPBF
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)： 7/26頁
文件大?。?/td> 399K
代理商： LTC3878IGN#TRPBF
LTC3878
3878fa
applicaTions inForMaTion
FaultConditions:CurrentLimitandFoldback
Themaximuminductorcurrentisinherentlylimitedina
currentmodecontrollerbythemaximumsensevoltage.
IntheLTC3878,themaximumsensevoltageiscontrolled
bythevoltageontheVRNGpin.Withvalleycurrentmode
control,themaximumsensevoltageandthesensere-
sistancedeterminethemaximumallowedinductorvalley
current.Thecorrespondingoutputcurrentlimitis:
I
V
R
I
LIMIT
SNS MAX
DS ON
T
L
=
+
(
)
( )
ρ
1
2
Thecurrentlimitvalueshouldbecheckedtoensurethat
ILIMIT(MIN) > IOUT(MAX). The current limit value should
begreaterthantheinductorcurrentrequiredtoproduce
maximum output power at the worst-case efficiency.
Worst-caseefficiencytypicallyoccursatthehighestVIN
andhighestambienttemperature.Itisimportanttocheck
forconsistencybetweentheassumedMOSFETjunction
temperaturesandtheresultingvalueofILIMITwhichheats
theMOSFETswitches.
Cautionshouldbeusedwhensettingthecurrentlimitbased
ontheRDS(ON)oftheMOSFETs.Themaximumcurrent
limitisdeterminedbytheminimumMOSFETon-resistance.
Datasheetstypicallyspecifynominalandmaximumvalues
forRDS(ON)butnotaminimum.Areasonableassumption
isthattheminimumRDS(ON)liesthesameamountbelow
thetypicalvalueasthemaximumliesaboveit.Consultthe
MOSFETmanufacturerforfurtherguidelines.
Tofurtherlimitcurrentintheeventofashortcircuitto
ground,theLTC3878includesfoldbackcurrentlimiting.
Iftheoutputfallsbymorethan50%,thenthemaximum
sensevoltageisprogressivelyloweredtoaboutone-sixth
ofitsfullvalue.
INTVCCRegulator
AninternalP-channellowdropoutregulatorproducesthe
5.3Vsupplythatpowersthedriversandinternalcircuitry
withintheLTC3878.TheINTVCCpincansupplyupto50mA
RMSandmustbebypassedtogroundwithaminimumof
1FlowESRtantalumorceramiccapacitor(10V,X5Ror
X7R).Outputcapacitancegreaterthan10Fisdiscouraged.
Goodbypassingisnecessarytosupplythehightransient
currentsrequiredbytheMOSFETgatedrivers.
ApplicationsusinglargeMOSFETswithahighinputvoltage
andhighfrequencyofoperationmaycausetheLTC3878
to exceed its maximum junction temperature rating or
RMScurrentrating.Incontinuousmodeoperation,this
currentisIGATECHG=fOP(Qg(TOP)+Qg(BOT)).Thejunction
temperaturecanbeestimatedfromtheequationsgiven
inNote2oftheElectricalCharacteristics.Forexample,
witha30Vinputsupply,theLTC3878islimitedtoless
than16.5mA:
TJ=70°C+(16.5mA)(30)(110°C/W)=125°C
UsingtheINTVCCregulatortosupplyexternalloadsgreater
than5mAisdiscouraged.INTVCCisdesignedtosupply
theLTC3878withminimalexternalloading.Whenusing
the regulator to supply larger external loads, carefully
consideralloperatingloadconditions.Duringloadsteps
andsoft-start,transientcurrentrequirementssignificantly
exceedtheRMSvalues.AdditionalloadingonINTVCCtakes
awayfromthedriveavailabletosourcegatechargeduring
highfrequencytransientloadsteps.
Soft-StartwiththeRUN/SSPin
TheRUN/SSpinbothenablestheLTC3878andprovidesa
meansofprogrammablecurrentlimitedsoft-start.Pulling
theRUN/SSpinbelow0.7VputstheLTC3878intoalow
quiescentcurrentshutdown(IQ<15A).Releasingthe
pinallowsaninternal1.2Acurrentsourcetochargeup
theexternaltimingcapacitorCSS.IfRUN/SShasbeen
pulledallthewaytoground,thereisadelaybeforestart-
ing.ThisdelayiscreatedbychargingCSSfromground
to1.5Vthrougha1.2Acurrentsource.
t
V
A
C
s F C
DELAY
SS
=
(
)
1 5
1 2
1 3
.
. /
WhenthevoltageonRUN/SSreaches1.5V,theLTC3878
beginstoswitch.ITHisclampedtobenogreaterthan
RUN/SS–0.6V,andthedevicebeginsswitchingwhen
ITHexceeds0.9V.AstheRUN/SSvoltagerisesto3V,the
clamponITHincreasesuntilitreachesthefull-scale2.4V
limitafteranadditionaldelayof1.3s/F.Duringthistime,
thesoft-startcurrentlimitissetto:
I
RUN SS
V
LIMIT SS
LIMIT
( )
/
– .
.
– .
=
(
)
0 6
0 8
2 4
0 88V
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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:- 標準包裝: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:- 標準包裝: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:- 標準包裝: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:- 標準包裝: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:- 標準包裝: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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