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)： 5/26頁
文件大小： 399K
代理商： LTC3878IGN#TRPBF
LTC3878
3878fa
applicaTions inForMaTion
Areasonablestartingpointistochoosearipplecurrent
thatisabout40%ofIOUT(MAX).Thelargestripplecurrent
occursatthehighestVIN.Toguaranteethatripplecurrent
doesnotexceedaspecifiedmaximum,theinductance
shouldbechosenaccordingto:
L
V
f
I
V
OUT
OP
IL MAX
OUT
IN MAX
=
–
(
)
(
)
1
OncethevalueforLisknown,thetypeofinductormust
beselected.Highefficiencyconvertersgenerallycannot
toleratethecorelossoflowcostpowderedironcores,
forcingtheuseofmoreexpensiveferritematerialssuch
asmolypermalloyorKoolMcores.Avarietyofinductors
designedforhighcurrent,lowvoltageapplicationsare
availablefrommanufacturerssuchasSumida,Panasonic,
Coiltronics,Coilcraft,Toko,Vishay,PulseandWurth.
InductorCoreSelection
Oncetheinductancevalueisdetermined,thetypeofin-
ductormustbeselected.Corelossisindependentofcore
sizeforafixedinductorvalue,butitisverydependent
on inductance selected. As inductance increases, core
losses go down. Unfortunately, increased inductance
requiresmoreturnsofwireandthereforecopperlosses
willincrease.
Ferritedesignshaveverylowcorelossandarepreferred
athighswitchingfrequencies,sodesigngoalscancon-
centrateoncopperlossandpreventingsaturation.Ferrite
corematerialsaturates“hard,”whichmeansthatinduc-
tancecollapsesabruptlywhenthepeakdesigncurrentis
exceeded.Thisresultsinanabruptincreaseininductor
ripplecurrentandconsequentoutputvoltageripple.Do
notallowthecoretosaturate!
CINandCOUTSelection
TheinputcapacitanceCINisrequiredtofilterthesquare
wavecurrentatthedrainofthetopMOSFET.UsealowESR
capacitorsizedtohandlethemaximumRMScurrent.
I
V
RMS
OUT MAX
OUT
IN
OUT
(
)
– 1
ThisformulahasamaximumatVIN=2VOUT,whereIRMS
=IOUT(MAX)/2.Thissimpleworst-caseconditioniscom-
monlyusedfordesignbecauseevensignificantdeviations
donotoffermuchrelief.Notethatripplecurrentratings
from capacitor manufacturers are often based on only
2000hoursoflife,whichmakesitadvisabletode-rate
thecapacitor.
TheselectionofCOUTisprimarilydeterminedbytheESR
requiredtominimizevoltagerippleandloadsteptransients.
The
VOUTisapproximatelyboundedby:
V
I ESR
f
C
OUT
L
OP
OUT
≤
+
1
8
Since
ILincreaseswithinputvoltage,theoutputripple
ishighestatmaximuminputvoltage.Typically,oncethe
ESRrequirementissatisfied,thecapacitanceisadequate
forfilteringandhasthenecessaryRMScurrentrating.
Multiplecapacitorsplacedinparallelmaybeneededto
meettheESRandRMScurrenthandlingrequirements.
Dry tantalum, specialty polymer, aluminum electrolytic
andceramiccapacitorsareallavailableinsurfacemount
packages. Specialty polymer capacitors offer very low
ESRbuthavelowerspecificcapacitancethanothertypes.
Tantalumcapacitorshavethehighestspecificcapacitance
butitisimportanttoonlyusetypesthathavebeensurge
tested for use in switching power supplies. Aluminum
electrolytic capacitors have significantly higher ESR,
butcanbeusedincost-sensitiveapplicationsproviding
thatconsiderationisgiventoripplecurrentratingsand
long-term reliability. Ceramic capacitors have excellent
lowESRcharacteristicsbutcanhaveahighvoltageco-
efficientandaudiblepiezoelectriceffects.ThehighQof
ceramiccapacitorswithtraceinductancecanalsoleadto
significantringing.Whenusedasinputcapacitors,care
mustbetakentoensurethatringingfrominrushcurrents
andswitchingdoesnotposeanovervoltagehazardtothe
powerswitchesandcontroller.Todampeninputvoltage
transients,addasmall5Fto40Faluminumelectrolytic
capacitorwithanESRintherangeof0.5Ωto2Ω.High
performancethough-holecapacitorsmayalsobeused,
butanadditionalceramiccapacitorinparallelisrecom-
mendedtoreducetheeffectofleadinductance.
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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)
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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)
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