LTC3858IUHPBF [Linear]
Low IQ, Dual 2-Phase Synchronous Step-Down Controller; 低IQ ，双两相同步降压型控制器
| 型号： | LTC3858IUHPBF |
| 厂家： | 
Linear |
| 描述： | Low IQ, Dual 2-Phase Synchronous Step-Down Controller |
| 文件： | 总38页 (文件大小：535K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LTC3858
Low I , Dual
Q
2-Phase Synchronous
Step-Down Controller
FeaTures
DescripTion
Theꢀ LTC®3858ꢀ isꢀ aꢀ highꢀ performanceꢀ dualꢀ step-downꢀ
switchingꢀregulatorꢀcontrollerꢀthatꢀdrivesꢀallꢀN-channelꢀ
synchronousꢀpowerꢀMOSFETꢀstages.ꢀAꢀconstantꢀfrequencyꢀ
currentꢀmodeꢀarchitectureꢀallowsꢀaꢀphase-lockableꢀfre-
quencyꢀofꢀupꢀtoꢀ850kHz.ꢀPowerꢀlossꢀandꢀnoiseꢀdueꢀtoꢀtheꢀ
inputꢀcapacitorꢀESRꢀareꢀminimizedꢀbyꢀoperatingꢀtheꢀtwoꢀ
controllerꢀoutputsꢀoutꢀofꢀphase.
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ꢀ Low Operating I : 170µA (One Channel On)
Q
n
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ꢀ Wide Output Voltage Range: 0.8V ≤ V
≤ 24V
OUT
ꢀ Wide V Range: 4V to 38V
IN
ꢀ R
or DCR Current Sensing
SENSE
ꢀ Out-of-PhaseꢀControllersꢀReduceꢀRequiredꢀInputꢀ
CapacitanceꢀandꢀPowerꢀSupplyꢀInducedꢀNoise
®
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ꢀ OPTI-LOOP ꢀCompensationꢀMinimizesꢀC
OUT
ꢀ Phase-LockableꢀFrequencyꢀ(75kHz-850kHz)
ꢀ ProgrammableꢀFixedꢀFrequencyꢀ(50kHz-900kHz)
ꢀ SelectableꢀContinuous,ꢀPulse-Skippingꢀorꢀ
BurstꢀMode®ꢀOperationꢀatꢀLightꢀLoads
Theꢀ170μAꢀno-loadꢀquiescentꢀcurrentꢀextendsꢀoperatingꢀ
lifeꢀinꢀbattery-poweredꢀsystems.ꢀOPTI-LOOPꢀcompensa-
tionꢀallowsꢀtheꢀtransientꢀresponseꢀtoꢀbeꢀoptimizedꢀoverꢀ
aꢀwideꢀrangeꢀofꢀoutputꢀcapacitanceꢀandꢀESRꢀvalues.ꢀTheꢀ
LTC3858ꢀfeaturesꢀaꢀprecisionꢀ0.8Vꢀreferenceꢀandꢀaꢀpowerꢀ
goodꢀoutputꢀindicator.ꢀAꢀwideꢀ4Vꢀtoꢀ38Vꢀinputꢀsupplyꢀrangeꢀ
encompassesꢀaꢀwideꢀrangeꢀofꢀintermediateꢀbusꢀvoltagesꢀ
andꢀbatteryꢀchemistries.
n
n
n
n
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n
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ꢀ VeryꢀLowꢀDropoutꢀOperation:ꢀ99%ꢀDutyꢀCycle
ꢀ AdjustableꢀOutputꢀVoltageꢀSoft-Start
ꢀ PowerꢀGoodꢀOutputꢀVoltageꢀMonitor
ꢀ OutputꢀOvervoltageꢀProtection
ꢀ OutputꢀLatch-OffꢀProtectionꢀDuringꢀShortꢀCircuit
Independentꢀsoft-startꢀpinsꢀforꢀeachꢀcontrollerꢀrampꢀtheꢀ
outputꢀvoltagesꢀduringꢀstart-up.ꢀTheꢀoutputꢀlatch-offꢀfeatureꢀ
protectsꢀtheꢀcircuitꢀinꢀshort-circuitꢀconditions.
ꢀ LowꢀShutdownꢀI :ꢀ8µA
Q
ꢀ InternalꢀLDOꢀPowersꢀGateꢀDriveꢀfromꢀV ꢀorꢀEXTV
IN
CC
ꢀ NoꢀCurrentꢀFoldbackꢀDuringꢀStart-Up
ꢀ Smallꢀ5mmꢀ×ꢀ5mmꢀQFNꢀPackage
Forꢀaꢀleadedꢀ28-leadꢀSSOPꢀpackageꢀwithꢀaꢀfixedꢀcurrentꢀ
limitꢀandꢀoneꢀPGOODꢀoutput,ꢀwithoutꢀphaseꢀmodulationꢀ
orꢀaꢀclockꢀoutput,ꢀseeꢀtheꢀLTC3858-1ꢀdataꢀsheet.
applicaTions
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L,ꢀLT,ꢀLTC,ꢀLTM,ꢀBurstꢀMode,ꢀOPTI-LOOP,ꢀµModule,ꢀPolyPhase,ꢀLinearꢀTechnologyꢀandꢀtheꢀLinearꢀ
ꢀ AutomotiveꢀSystems
logoꢀareꢀregisteredꢀtrademarksꢀandꢀNoꢀR ꢀandꢀUltraFastꢀareꢀtrademarksꢀofꢀLinearꢀTechnologyꢀ
SENSE
n
ꢀ BatteryꢀOperatedꢀDigitalꢀDevices
Corporation.ꢀAllꢀotherꢀtrademarksꢀareꢀtheꢀpropertyꢀofꢀtheirꢀrespectiveꢀowners.ꢀProtectedꢀbyꢀU.S.ꢀ
Patents,ꢀincludingꢀ5481178,ꢀ5705919,ꢀ5929620,ꢀ6100678,ꢀ6144194,ꢀ6177787,ꢀ6304066,ꢀ6580258.
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ꢀ DistributedꢀDCꢀPowerꢀSystems
Typical applicaTion
High Efficiency Dual 8.5V/3.3V Step-Down Converter
V
Efficiency and Power Loss
IN
9V TO 38V
22µF
50V
vs Load Current
4.7µF
V
INTV
CC
100
90
10000
1000
100
10
IN
TG1
TG2
0.1µF
0.1µF
BOOST1
SW1
BOOST2
SW2
3.3µH
7.2µH
80
EFFICIENCY
70
BG1
BG2
60
50
LTC3858
POWER LOSS
PGND
+
+
40
30
20
10
0
SENSE1
SENSE1
SENSE2
0.01Ω
193k
0.007Ω
–
1
–
V
8.5V
3.5A
SENSE2
OUT2
V
V
IN
V
= 12V
= 3.3V
OUT1
3.3V
5A
V
V
FB1
FB2
OUT
FIGURE 12 CIRCUIT
62.5k
I
I
TH2
TH1
SS1
0.1
150µF
680pF
15k
680pF
150µF
SGND
SS2
0.0001 0.001
0.01
0.1 10
1
20k
OUTPUT CURRENT (A)
20k
15k
0.1µF
0.1µF
3858 TA01b
3858 TA01
3858fa
ꢀ
LTC3858
absoluTe MaxiMuM raTings
pin conFiguraTion
(Note 1)
TOP VIEW
InputꢀSupplyꢀVoltageꢀ(V )ꢀ......................... –0.3Vꢀtoꢀ40V
IN
TopsideꢀDriverꢀVoltagesꢀ
ꢀ BOOST1,ꢀBOOST2ꢀꢀ................................. –0.3Vꢀtoꢀ46V
SwitchꢀVoltageꢀ(SW1,ꢀSW2)ꢀꢀ........................ –5Vꢀtoꢀ40V
(BOOST1-SW1),ꢀ(BOOST2-SW2)ꢀꢀ................ –0.3Vꢀtoꢀ6V
RUN1,ꢀRUN2ꢀꢀ............................................... –0.3Vꢀtoꢀ8V
ꢀ MaximumꢀCurrentꢀSourcedꢀintoꢀPinꢀ
32 31 30 29 28 27 26 25
–
SENSE1
FREQ
1
2
3
4
5
6
7
8
24 BOOST1
23 BG1
PHASMD
CLKOUT
PLLIN/MODE
SGND
V
IN
22
21
PGND
33
SGND
20 EXTV
ꢀ fromꢀSourceꢀ>8V...............................................100µA
CC
CC
+
–
+
–
INTV
19
18 BG2
17 BOOST2
SENSE1 ,ꢀSENSE2 ,ꢀSENSE1
RUN1
SENSE2 ꢀVoltagesꢀ...................................... –0.3Vꢀtoꢀ28V
RUN2
PLLIN/MODE,ꢀFREQꢀVoltagesꢀꢀ.............. –0.3VꢀtoꢀINTV
CC
CC
9
10 11 12 13 14 15 16
I
,ꢀPHASMDꢀVoltagesꢀꢀ....................... –0.3VꢀtoꢀINTV
LIM
EXTV ꢀꢀ...................................................... –0.3Vꢀtoꢀ14V
CC
I
,ꢀI ,V ,ꢀV ꢀVoltagesꢀ...................... –0.3Vꢀtoꢀ6V
TH1 TH2 FB1 FB2
UH PACKAGE
32-LEAD (5mm s 5mm) PLASTIC QFN
PGOOD1,ꢀPGOOD2ꢀVoltagesꢀꢀ....................... –0.3Vꢀtoꢀ6V
ꢀ
T ꢀ=ꢀ125°C,ꢀθ ꢀ=ꢀ34°C/W
JMAX JA
SS1,ꢀSS2,ꢀINTV ꢀVoltagesꢀꢀ......................... –0.3Vꢀtoꢀ6V
CC
EXPOSEDꢀPADꢀ(PINꢀ33)ꢀISꢀSGND,ꢀMUSTꢀBEꢀSOLDEREDꢀTOꢀPCB
OperatingꢀJunctionꢀTemperatureꢀRangeꢀ
(Noteꢀ2)ꢀ.................................................. –40°Cꢀtoꢀ125°C
MaximumꢀJunctionꢀTemperatureꢀ(Noteꢀ3)ꢀ............ 125°C
StorageꢀTemperatureꢀRangeꢀ................... –65°Cꢀtoꢀ150°C
orDer inForMaTion
LEAD FREE FINISH
LTC3858EUH#PBF
LTC3858IUH#PBF
TAPE AND REEL
PART MARKING*
3858
PACKAGE DESCRIPTION
TEMPERATURE RANGE
–40°Cꢀtoꢀ125°C
LTC3858EUH#TRPBF
LTC3858IUH#TRPBF
32-Leadꢀ(5mmꢀ×ꢀ5mm)ꢀPlasticꢀQFN
32-Leadꢀ(5mmꢀ×ꢀ5mm)ꢀPlasticꢀQFN
3858
–40°Cꢀtoꢀ125°C
ConsultꢀLTCꢀMarketingꢀforꢀpartsꢀspecifiedꢀwithꢀwiderꢀoperatingꢀtemperatureꢀranges.ꢀ*Theꢀtemperatureꢀgradeꢀisꢀidentifiedꢀbyꢀaꢀlabelꢀonꢀtheꢀshippingꢀcontainer.
ConsultꢀLTCꢀMarketingꢀforꢀinformationꢀonꢀnon-standardꢀleadꢀbasedꢀfinishꢀparts.
Forꢀmoreꢀinformationꢀonꢀleadꢀfreeꢀpartꢀmarking,ꢀgoꢀto:ꢀhttp://www.linear.com/leadfree/ꢀꢀ
Forꢀmoreꢀinformationꢀonꢀtapeꢀandꢀreelꢀspecifications,ꢀgoꢀto:ꢀhttp://www.linear.com/tapeandreel/
elecTrical characTerisTics The l denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at TA = 25°C. VIN = 12V, VRUN1,2 = 5V, EXTVCC = 0V unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
V
InputꢀSupplyꢀOperatingꢀVoltageꢀRange
RegulatedꢀFeedbackꢀVoltage
4
38
V
IN
(Noteꢀ4)ꢀI
ꢀ=ꢀ1.2Vꢀ
ꢀ
ꢀ
ꢀ
ꢀ
FB1,2
TH1,2
ꢀ–40°Cꢀtoꢀ125°Cꢀ
ꢀ–40°Cꢀtoꢀ85°C
l
0.788ꢀ
0.792
0.800ꢀ
0.800
0.812ꢀ
0.808
Vꢀ
V
I
FeedbackꢀCurrent
(Noteꢀ4)
5
50
nA
FB1,2
V
ReferenceꢀVoltageꢀLineꢀRegulation
(Noteꢀ4)ꢀV ꢀ=ꢀ4.5Vꢀtoꢀ38V
0.002
0.02
%/V
REFLNREG
IN
3858fa
ꢁ
LTC3858
elecTrical characTerisTics The l denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at TA = 25°C. VIN = 12V, VRUN1,2 = 5V, EXTVCC = 0V unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
OutputꢀVoltageꢀLoadꢀRegulation
(Note4)ꢀ
ꢀ
ꢀ
ꢀ
LOADREG
l
l
MeasuredꢀinꢀServoꢀLoop,ꢀꢀ
0.01
0.1
%
∆I ꢀVoltageꢀ=ꢀ1.2Vꢀtoꢀ0.7V
TH
(Note4)ꢀ
ꢀ
ꢀ
ꢀ
%
MeasuredꢀinꢀServoꢀLoop,ꢀꢀ
–0.01
–0.1
∆I ꢀVoltageꢀ=ꢀ1.2Vꢀtoꢀ2V
TH
g
ꢀ
TransconductanceꢀAmplifierꢀg
InputꢀDCꢀSupplyꢀCurrent
(Noteꢀ4)ꢀI
ꢀ=ꢀ1.2V,ꢀSink/Sourceꢀ=ꢀ5µA
TH1,2
2
mmho
mA
m1,2
m
I
(Noteꢀ5)
Q
PulseꢀSkipꢀorꢀForcedꢀContinuousꢀModeꢀ
(OneꢀChannelꢀOn)
RUN1ꢀ=ꢀ5VꢀandꢀRUN2ꢀ=ꢀ0Vꢀorꢀꢀ
RUN1ꢀ=ꢀ0VꢀandꢀRUN2ꢀ=ꢀ5V,ꢀꢀ
1.3
V
ꢀ=ꢀ0.83Vꢀ(NoꢀLoad)
FB1
PulseꢀSkipꢀorꢀForcedꢀContinuousꢀModeꢀ
(BothꢀChannelsꢀOn)
RUN1,2ꢀ=ꢀ5V,ꢀV
ꢀ=ꢀ0.83Vꢀ(NoꢀLoad)
2
mA
µA
FB1,2
SleepꢀModeꢀ(OneꢀChannelꢀOn)
RUN1ꢀ=ꢀ5VꢀandꢀRUN2ꢀ=ꢀ0Vꢀorꢀꢀ
RUN1ꢀ=ꢀ0VꢀandꢀRUN2ꢀ=ꢀ5V,ꢀꢀ
170
250
V
ꢀ=ꢀ0.83Vꢀ(NoꢀLoad)
FB1
SleepꢀModeꢀ(BothꢀChannelsꢀOn)
Shutdown
RUN1,2ꢀ=ꢀ5V,ꢀV
RUN1,2ꢀ=ꢀ0V
ꢀ=ꢀ0.83Vꢀ(NoꢀLoad)
FB1,2
300
8
450
20
µA
µA
l
l
UVLO
UndervoltageꢀLockout
INTV ꢀRampingꢀUpꢀ
ꢀ
4.0ꢀ
3.8
4.2ꢀ
4
Vꢀ
V
CC
INTV ꢀRampingꢀDown
3.6
CC
V
FeedbackꢀOvervoltageꢀProtection
MeasuredꢀatꢀV
EachꢀChannel
EachꢀChannelꢀ
,ꢀRelativeꢀtoꢀRegulatedꢀV
FB1,2
7
10
13
1
%
OVL
FB1,2
+
–
+
I
I
SENSE ꢀPinsꢀCurrent
µA
SENSE
SENSE
–
SENSE ꢀPinsꢀCurrent
ꢀ
ꢀ
ꢀ
ꢀ
µAꢀ
µA
V
V
ꢀ<ꢀINTV ꢀ–ꢀ0.5Vꢀ
1ꢀ
OUT1,2
OUT1,2
CC
CC
ꢀ>ꢀINTV ꢀ+ꢀ0.5V
540
700
DF
MaximumꢀDutyꢀFactor
InꢀDropout,ꢀFREQꢀ=ꢀ0V
98
0.7
99.4
1.0
1.28
50
%
µA
V
MAX
I
Soft-StartꢀChargeꢀCurrent
RUNꢀPinꢀOnꢀThresholdꢀVoltage
V ꢀ=ꢀ0V
SS1,2
1.4
SS1,2
l
V
V
V
V
ꢀOn
V
,ꢀV ꢀRising
RUN1 RUN2
1.23
1.33
RUN1,2
RUN1,2
SS1,2
ꢀHyst RUNꢀPinꢀHysteresisꢀVoltage
mV
V
ꢀLA
SSꢀPinꢀLatch-OffꢀArmingꢀThresholdꢀVoltage
SSꢀPinꢀLatch-OffꢀThresholdꢀVoltage
SSꢀDischargeꢀCurrent
V
V
,ꢀV ꢀRisingꢀfromꢀ1V
1.9
1.3
7
2
2.1
1.7
13
SS1 SS2
ꢀLT
,ꢀV ꢀFallingꢀfromꢀ2V
SS1 SS2
1.5
10
V
SS1,2
I
ꢀLT
Short-CircuitꢀConditionꢀV
ꢀ=ꢀ0.5V,ꢀꢀ
FB1,2
µA
DSC1,2
V
ꢀ=ꢀ4.5V
SS1,2
l
l
l
V
MaximumꢀCurrentꢀSenseꢀThresholdꢀVoltage
V
FB1,2
V
FB1,2
V
FB1,2
ꢀ=ꢀ0.7V,ꢀV
ꢀ=ꢀ0.7V,ꢀV
ꢀ=ꢀ0.7V,ꢀV
–, –ꢀ=ꢀ3.3V,ꢀI ꢀ=ꢀ0ꢀ
22ꢀ
43ꢀ
64
30ꢀ
50ꢀ
75
36ꢀ
57ꢀ
86
mVꢀ
mVꢀ
mV
SENSE(MAX)
SENSE1
SENSE1
SENSE1
2
LIM
–, –ꢀ=ꢀ3.3V,ꢀI ꢀ=ꢀFLOATꢀ
2
LIM
–, –ꢀ=ꢀ3.3V,ꢀI ꢀ=ꢀINTV
2
LIM
CC
Gate Driver
TG1,2
Pull-UpꢀOn-Resistanceꢀ
Pull-DownꢀOn-Resistance
2.5ꢀ
1.5
Ωꢀ
Ω
BG1,2
Pull-UpꢀOn-Resistanceꢀ
Pull-DownꢀOn-Resistance
2.4ꢀ
1.1
Ωꢀ
Ω
ꢀ
TGꢀTransistionꢀTime:ꢀ
ꢀRiseꢀTimeꢀ
ꢀFallꢀTime
(Noteꢀ6)ꢀ
ꢀ
ꢀ
nsꢀ
ns
TG1,2ꢀt ꢀ
C
C
ꢀ=ꢀ3300pFꢀ
25ꢀ
16
r
LOAD
LOAD
TG1,2ꢀt
ꢀ=ꢀ3300pF
f
ꢀ
BGꢀTransistionꢀTime:ꢀ
ꢀRiseꢀTimeꢀ
ꢀFallꢀTime
(Noteꢀ6)ꢀ
LOAD
LOAD
ꢀ
ꢀ
nsꢀ
ns
BG1,2ꢀt ꢀ
C
C
ꢀ=ꢀ3300pFꢀ
ꢀ=ꢀ3300pF
28ꢀ
13
r
BG1,2ꢀt
f
3858fa
ꢂ
LTC3858
elecTrical characTerisTics The l denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at TA = 25°C. VIN = 12V, VRUN1,2 = 5V, EXTVCC = 0V unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
TG/BGꢀt
TopꢀGateꢀOffꢀtoꢀBottomꢀGateꢀOnꢀDelayꢀ
SynchronousꢀSwitch-OnꢀDelayꢀTime
C ꢀ=ꢀ3300pFꢀEachꢀDriver
LOAD
30
ns
1D
BG/TGꢀt
BottomꢀGateꢀOffꢀtoꢀTopꢀGateꢀOnꢀDelayꢀ
TopꢀSwitch-OnꢀDelayꢀTime
C
ꢀ=ꢀ3300pFꢀEachꢀDriver
30
95
ns
ns
1D
LOAD
t
MinimumꢀOn-Time
(Noteꢀ7)
ON(MIN)
INTV Linear Regulator
CC
V
V
V
V
V
V
InternalꢀV ꢀVoltage
6Vꢀ<ꢀV ꢀ<ꢀ38V,ꢀV ꢀ=ꢀ0V
EXTVCC
4.85
4.85
4.5
5.1
0.7
5.1
0.6
4.7
250
5.35
1.1
V
%
V
INTVCCVIN
LDOVIN
CC
IN
INTV ꢀLoadꢀRegulation
I
ꢀ=ꢀ0mAꢀtoꢀ50mA,ꢀV
ꢀ=ꢀ0V
CC
CC
EXTVCC
InternalꢀV ꢀVoltage
6Vꢀ<ꢀV ꢀ<ꢀ13V
EXTVCC
5.35
1.1
INTVCCEXT
LDOEXT
CC
INTV ꢀLoadꢀRegulation
I
ꢀ=ꢀ0mAꢀtoꢀ50mA,ꢀV
CC
ꢀ=ꢀ8.5V
%
V
CC
EXTVCC
EXTV ꢀSwitchoverꢀVoltage
EXTV ꢀRampingꢀPositive
4.9
EXTVCC
CC
CC
EXTV ꢀHysteresisꢀVoltage
mV
LDOHYS
CC
Oscillator and Phase-Locked Loop
f
f
f
f
f
f
ProgrammableꢀFrequency
ProgrammableꢀFrequency
ProgrammableꢀFrequency
LowꢀFixedꢀFrequency
R
R
R
ꢀ=ꢀ25k,ꢀPLLIN/MODEꢀ=ꢀDCꢀVoltage
ꢀ=ꢀ65k,ꢀPLLIN/MODEꢀ=ꢀDCꢀVoltage
ꢀ=ꢀ105k,ꢀPLLIN/MODEꢀ=ꢀDCꢀVoltage
ꢀ=ꢀ0V,ꢀPLLIN/MODEꢀ=ꢀDCꢀVoltage
105
440
835
350
535
kHz
kHz
kHz
kHz
kHz
kHz
25kΩ
65kΩ
105kΩ
LOW
FREQ
FREQ
FREQ
FREQ
FREQ
375
505
V
V
320
485
75
380
585
850
HighꢀFixedꢀFrequency
ꢀ=ꢀINTV ,ꢀPLLIN/MODEꢀ=ꢀDCꢀVoltage
CC
HIGH
SYNC
l
SynchronizableꢀFrequency
PLLIN/MODEꢀ=ꢀExternalꢀClock
PGOOD1 and PGOOD2 Outputs
V
PGOODꢀVoltageꢀLow
PGOODꢀLeakageꢀCurrent
PGOODꢀTripꢀLevel
I
ꢀ=ꢀ2mA
0.2
0.4
1
V
PGL
PGOOD
I
V
ꢀ=ꢀ5V
PGOOD
µA
PGOOD
V
PG
V
ꢀwithꢀRespectꢀtoꢀSetꢀRegulatedꢀVoltageꢀ
FB
ꢀ
ꢀ
ꢀ
ꢀ
ꢀV ꢀRampingꢀNegativeꢀ
–13
–10ꢀ
2.5
–7
%ꢀ
%
FB
ꢀHysteresis
V
ꢀwithꢀRespectꢀtoꢀSetꢀRegulatedꢀVoltageꢀ
FB
ꢀ
7
ꢀ
ꢀ
ꢀ
FB
ꢀV ꢀRampingꢀPositiveꢀ
10ꢀ
2.5
13
%ꢀ
%
ꢀHysteresis
t
PG
DelayꢀforꢀReportingꢀaꢀFaultꢀ(PGOODꢀLow)
25
µs
Note 1:ꢀStressesꢀbeyondꢀthoseꢀlistedꢀunderꢀAbsoluteꢀMaximumꢀRatingsꢀ
mayꢀcauseꢀpermanentꢀdamageꢀtoꢀtheꢀdevice.ꢀExposureꢀtoꢀanyꢀAbsoluteꢀ
MaximumꢀRatingsꢀforꢀextendedꢀperiodsꢀmayꢀaffectꢀdeviceꢀreliabilityꢀandꢀ
lifetime.ꢀ
Note 4:ꢀTheꢀLTC3858ꢀisꢀtestedꢀinꢀaꢀfeedbackꢀloopꢀthatꢀservosꢀV
ꢀtoꢀaꢀ
ITH1,2
specifiedꢀvoltageꢀandꢀmeasuresꢀtheꢀresultantꢀV .ꢀTheꢀspecificationꢀatꢀ
FB1,2
85°Cꢀisꢀnotꢀtestedꢀinꢀproduction.ꢀThisꢀspecificationꢀisꢀassuredꢀbyꢀdesign,ꢀ
characterizationꢀandꢀcorrelationꢀtoꢀproductionꢀtestingꢀatꢀ125°C.
Note 2:ꢀTheꢀLTC3858Eꢀisꢀguaranteedꢀtoꢀmeetꢀperformanceꢀspecificationsꢀ
fromꢀ0°Cꢀtoꢀ85°C.ꢀSpecificationsꢀoverꢀtheꢀ–40°Cꢀtoꢀ125°Cꢀoperatingꢀ
junctionꢀtemperatureꢀrangeꢀareꢀassuredꢀbyꢀdesign,ꢀcharacterizationꢀandꢀ
correlationꢀwithꢀstatisticalꢀprocessꢀcontrols.ꢀTheꢀLTC3858Iꢀisꢀguaranteedꢀ
overꢀtheꢀfullꢀ–40°Cꢀtoꢀ125°Cꢀoperatingꢀjunctionꢀtemperatureꢀrange.
Note 5:ꢀDynamicꢀsupplyꢀcurrentꢀisꢀhigherꢀdueꢀtoꢀtheꢀgateꢀchargeꢀbeingꢀ
deliveredꢀatꢀtheꢀswitchingꢀfrequency.ꢀSeeꢀApplicationsꢀinformation.
Note 6:ꢀRiseꢀandꢀfallꢀtimesꢀareꢀmeasuredꢀusingꢀ10%ꢀandꢀ90%ꢀlevels.ꢀDelayꢀ
timesꢀareꢀmeasuredꢀusingꢀ50%ꢀlevels
Note 7:ꢀTheꢀminimumꢀon-timeꢀconditionꢀisꢀspecifiedꢀforꢀanꢀinductorꢀ
Note 3:ꢀT ꢀisꢀcalculatedꢀfromꢀtheꢀambientꢀtemperatureꢀT ꢀandꢀpowerꢀ
J
A
peak-to-peakꢀrippleꢀcurrentꢀ≥ꢀofꢀ40%ꢀI ꢀ(SeeꢀMinimumꢀOn-Timeꢀ
MAX
dissipationꢀP ꢀaccordingꢀtoꢀtheꢀfollowingꢀformula:
D
ConsiderationsꢀinꢀtheꢀApplicationsꢀInformationꢀsection).
ꢀ
T ꢀ=ꢀT ꢀ+ꢀ(P •ꢀ34°C/W)
J A Dꢀ
3858fa
ꢃ
LTC3858
Typical perForMance characTerisTics
Efficiency and Power Loss
vs Output Current
Efficiency vs Output Current
100
90
100
90
10000
1000
100
10
FIGURE 12 CIRCUIT
V
V
= 12V
IN
OUT
V
IN
= 5V
= 3.3V
80
80
70
70
V
IN
= 12V
60
50
60
50
Burst Mode
OPERATION
PULSE-
SKIPPING
MODE
FORCED
40
30
20
10
0
40
30
20
10
0
1
V
= 3.3V
CONTINUOUS
MODE
OUT
FIGURE 12 CIRCUIT
0.1
0.0001 0.001
0.01
0.1 10
1
0.0001 0.001
0.01
0.1
1
10
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
3858 G02
3858 G01
Load Step
(Forced Continuous Mode)
Efficiency vs Input Voltage
Load Step (Burst Mode Operation)
98
96
94
92
90
88
86
84
82
80
FIGURE 12 CIRCUIT
V
= 3.3V
OUT
OUT
V
V
OUT
OUT
I
= 4A
100mV/DIV
AC-
100mV/DIV
AC-
COUPLED
COUPLED
I
L
I
L
2A/DIV
2A/DIV
3858 G05
3858 G04
V
= 3.3V
20µs/DIV
20 25
INPUT VOLTAGE (V)
0
5
10 15
30 35 40
V
= 3.3V
20µs/DIV
OUT
OUT
FIGURE 12 CIRCUIT
FIGURE 12 CIRCUIT
3858 G03
Load Step (Pulse-Skipping Mode)
Inductor Current at Light Load
Soft-Start
V
OUT
FORCED
CONTINUOUS
MODE
V
OUT2
100mV/DIV
AC-
2V/DIV
COUPLED
Burst Mode
OPERATION
2A/DIV
V
OUT1
2V/DIV
I
L
2A/DIV
PULSE-
SKIPPING
MODE
3858 G07
3858 G08
3858 G06
V
I
= 3.3V
2µs/DIV
20ms/DIV
FIGURE 12 CIRCUIT
V
= 3.3V
20µs/DIV
OUT
LOAD
OUT
= 200µA
FIGURE 12 CIRCUIT
FIGURE 12 CIRCUIT
3858fa
ꢄ
LTC3858
Typical perForMance characTerisTics
Total Input Supply Current
vs Input Voltage
EXTVCC Switchover and INTVCC
Voltages vs Temperature
INTVCC Line Regulation
400
5.6
5.2
5.2
5.1
5.1
FIGURE 12 CIRCUIT
= 3.3V
V
OUT
350
300
5.4
5.2
ONE CHANNEL ON
INTV
CC
300µA LOAD
250
200
150
100
50
5.0
4.8
4.6
4.4
4.2
EXTV RISING
CC
NO LOAD
EXTV FALLING
CC
5.0
0
4.0
10
15
25
30
35
40
0
5
10 15 20 25 30 35 40
INPUT VOLTAGE (V)
5
20
–20
5
55
80 105 130
–45
30
INPUT VOLTAGE (V)
TEMPERATURE (°C)
3858 G12
3858 G10
3858 G11
Maximum Current Sense Voltage
vs ITH Voltage
Maximum Current Sense
Threshold vs Duty Cycle
SENSE– Pin Input Bias Current
80
60
40
20
80
60
40
20
0
0
–50
PULSE SKIPPING
FORCED CONTINUOUS
Burst Mode OPERATION
(FALLING)
Burst Mode OPERATION
(RISING)
I
= INTV
CC
LIM
–100
–150
–200
–250
–300
–350
–400
–450
–500
–550
–600
I
= FLOAT
LIM
I
= GND
LIM
I
= GND
LIM
0
–20
–40
I
= FLOAT
LIM
LIM
I
= INTV
CC
5% DUTY CYCLE
0
10
15
20
25
0.8
1.2 1.4
5
10 20
50
60 70 80 90 100
0
0.2 0.4 0.6
1.0
0
30 40
V
COMMON MODE VOLTAGE (V)
I
TH
PIN VOLTAGE
DUTY CYCLE (%)
SENSE
3858 G14
3858 G13
3858 G15
Shutdown Current vs Temperature
Foldback Current Limit
Quiescent Current vs Temperature
230
210
190
170
150
130
110
90
80
70
60
50
40
30
20
10
10
9
PLLIN/MODE = 0
I
= INTV
V
V
= 12V
LIM
CC
IN
OUT
= 3.3V
ONE CHANNEL ON
8
I
= FLOAT
LIM
7
I
= GND
LIM
6
5
4
0
–45 –20
5
30
55
80 105 130
–45
30
55
80
105 130
–20
5
0
0.1 0.2 0.3 0.4 0.5
0.9
0.6 0.7 0.8
TEMPERATURE (°C)
FEEDBACK VOLTAGE (V)
TEMPERATURE (°C)
3858 G17
3858 G18
3858 G16
3858fa
ꢅ
LTC3858
Typical perForMance characTerisTics
Regulated Feedback Voltage
vs Temperature
Soft-Start Pull-Up Current
vs Temperature
Shutdown (RUN) Threshold
vs Temperature
1.40
1.35
1.30
1.25
1.20
1.15
1.10
1.05
1.00
0.95
0.90
808
1.20
806
804
1.15
1.10
802
800
798
796
794
1.05
1.00
0.95
0.90
0.85
792
0.80
–20
5
55
80 105 130
–45
5
30
55
80 105 130
–45 –20
5
30
55
80 105 130
–45
30
–20
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
3858 G20
22554 G21
3858 G19
SENSE– Pin Input Current
vs Temperature
Shutdown Input Current
vs Input Voltage
Oscillator Frequency
vs Temperature
50
0
–50
14
12
800
V
OUT
= 3.3V
700
600
–100
–150
–200
–250
–300
–350
–400
–450
–500
–550
–600
FREQ = INTV
CC
10
8
500
400
300
200
100
FREQ = GND
6
4
2
V
= 28V
55
OUT
0
0
–45 –20
5
30
80 105 130
25
INPUT VOLTAGE (V)
35
40
–20
5
55
80 105 130
5
10
15
20
30
–45
30
TEMPERATURE (°C)
TEMPERATURE (°C)
3858 G22
3858 G23
3858 G24
Oscillator Frequency
vs Input Voltage
Undervoltage Lockout Threshold
vs Temperature
4.4
356
354
352
350
FREQ = GND
4.3
4.2
4.1
4.0
3.9
3.8
3.7
3.6
3.5
3.4
348
346
344
–45
5
30
55
80 105 130
–20
25
35
40
5
10
15
20
30
TEMPERATURE (°C)
INPUT VOLTAGE (V)
3858 G25
3858 G28
3858fa
ꢆ
LTC3858
Typical perForMance characTerisTics
Latch-Off Threshold Voltages
vs Temperature
INTVCC and EXTVCC
vs Load Current
2.3
2.2
2.1
2.0
1.9
1.8
1.7
1.6
1.5
1.4
1.3
1.2
5.20
5.15
5.10
V
= 12V
IN
ARMING THRESHOLD
EXTV = 0V
CC
5.05
5.00
4.95
LATCH-OFF THRESHOLD
EXTV = 8V
CC
0
20 40 60 80 100 120 140 160 180 200
–45
5
30
55
80
130
–20
105
TEMPERATURE (°C)
LOAD CURRENT (mA)
3858 G26
3858 G27
pin FuncTions
–
–
CLKOUT (Pin 4):ꢀOutputꢀclockꢀsignalꢀavailableꢀtoꢀdaisy-
SENSE1 , SENSE2 (Pin 1, Pin 9):ꢀTheꢀ(–)ꢀInputꢀtoꢀtheꢀ
chainꢀotherꢀcontrollerꢀICsꢀforꢀadditionalꢀMOSFETꢀdriverꢀ
Differentialꢀ Currentꢀ Comparators.ꢀ Whenꢀ greaterꢀ thanꢀ
–
stages/phases.ꢀTheꢀoutputꢀlevelsꢀswingꢀfromꢀINTV ꢀtoꢀ
INTV ꢀ–ꢀ0.5V,ꢀtheꢀSENSE ꢀpinꢀsuppliesꢀcurrentꢀtoꢀtheꢀ
CC
CC
ground.ꢀ
currentꢀcomparator.
PLLIN/MODE (Pin 5):ꢀExternalꢀSynchronizationꢀInputꢀtoꢀ
PhaseꢀDetectorꢀandꢀForcedꢀContinuousꢀModeꢀInput.ꢀWhenꢀ
anꢀexternalꢀclockꢀisꢀappliedꢀtoꢀthisꢀpin,ꢀtheꢀphase-lockedꢀ
loopꢀwillꢀforceꢀtheꢀrisingꢀTG1ꢀsignalꢀtoꢀbeꢀsynchronizedꢀ
withꢀtheꢀrisingꢀedgeꢀofꢀtheꢀexternalꢀclock.ꢀWhenꢀnotꢀsyn-
chronizingꢀtoꢀanꢀexternalꢀclock,ꢀthisꢀinput,ꢀwhichꢀactsꢀonꢀ
bothꢀcontrollers,ꢀdeterminesꢀhowꢀtheꢀLTC3858ꢀoperatesꢀatꢀ
lightꢀloads.ꢀPullingꢀthisꢀpinꢀtoꢀgroundꢀselectsꢀBurstꢀModeꢀ
operation.ꢀAnꢀinternalꢀ100kꢀresistorꢀtoꢀgroundꢀalsoꢀinvokesꢀ
BurstꢀModeꢀoperationꢀwhenꢀtheꢀpinꢀisꢀfloated.ꢀTyingꢀthisꢀpinꢀ
FREQ (Pin 2):ꢀTheꢀFrequencyꢀControlꢀPinꢀforꢀtheꢀInternalꢀ
Voltage-ControlledꢀOscillatorꢀ(VCO).ꢀConnectingꢀthisꢀpinꢀ
toꢀGNDꢀforcesꢀtheꢀVCOꢀtoꢀaꢀfixedꢀlowꢀfrequencyꢀofꢀ350kHz.ꢀ
ConnectingꢀthisꢀpinꢀtoꢀINTV ꢀforcesꢀtheꢀVCOꢀtoꢀaꢀfixedꢀ
CC
highꢀ frequencyꢀ ofꢀ 535kHz.ꢀ Otherꢀ frequenciesꢀ betweenꢀ
50kHzꢀandꢀ900kHzꢀcanꢀbeꢀprogrammedꢀusingꢀaꢀresistorꢀ
betweenꢀFREQꢀandꢀGND.ꢀAnꢀinternalꢀ20µAꢀpull-upꢀcurrentꢀ
developsꢀtheꢀvoltageꢀtoꢀbeꢀusedꢀbyꢀtheꢀVCOꢀtoꢀcontrolꢀtheꢀ
frequency
PHASMD (Pin 3):ꢀControlꢀinputꢀtoꢀphaseꢀselectorꢀwhichꢀ
determinesꢀtheꢀphaseꢀrelationshipsꢀbetweenꢀcontrollerꢀ1,ꢀ
controllerꢀ2ꢀandꢀtheꢀCLKOUTꢀsignal.ꢀPullingꢀthisꢀpinꢀtoꢀ
groundꢀforcesꢀTG2ꢀandꢀCLKOUTꢀtoꢀbeꢀoutꢀofꢀphaseꢀ180°ꢀ
toꢀINTV ꢀforcesꢀcontinuousꢀinductorꢀcurrentꢀoperation.ꢀ
CC
Tyingꢀthisꢀpinꢀtoꢀaꢀvoltageꢀgreaterꢀthanꢀ1.2Vꢀandꢀlessꢀthanꢀ
INTV ꢀ–ꢀ1.3Vꢀselectsꢀpulse-skippingꢀoperation.ꢀ
CC
SGND (Pin 6, Exposed Pad Pin 33):ꢀSmall-signalꢀgroundꢀ
commonꢀtoꢀbothꢀcontrollers,ꢀmustꢀbeꢀroutedꢀseparatelyꢀ
fromꢀhighꢀcurrentꢀgroundsꢀtoꢀtheꢀcommonꢀ(–)ꢀterminalsꢀ
andꢀ60°ꢀwithꢀrespectꢀtoꢀTG1.ꢀConnectingꢀthisꢀpinꢀtoꢀINTV ꢀ
CC
forcesꢀTG2ꢀandꢀCLKOUTꢀtoꢀbeꢀoutꢀofꢀphaseꢀ240°ꢀandꢀ120°ꢀ
withꢀ respectꢀ toꢀ TG1.ꢀ Floatingꢀ thisꢀ pinꢀ forcesꢀ TG2ꢀ andꢀ
CLKOUTꢀtoꢀbeꢀoutꢀofꢀphaseꢀ180°ꢀandꢀ90°ꢀwithꢀrespectꢀtoꢀ
TG1.ꢀReferꢀtoꢀtheꢀTableꢀ1.ꢀ
ofꢀtheꢀC ꢀcapacitors.ꢀTheꢀexposedꢀpadꢀmustꢀbeꢀsolderedꢀ
IN
toꢀtheꢀPCBꢀforꢀratedꢀthermalꢀperformance.
3858fa
ꢇ
LTC3858
pin FuncTions
RUN1, RUN2 (Pin 7, Pin 8):ꢀDigitalꢀRunꢀControlꢀInputsꢀforꢀ
EachꢀController.ꢀForcingꢀeitherꢀofꢀtheseꢀpinsꢀbelowꢀ1.2Vꢀ
shutsꢀdownꢀthatꢀcontroller.ꢀForcingꢀbothꢀofꢀtheseꢀpinsꢀbelowꢀ
0.7VꢀshutsꢀdownꢀtheꢀentireꢀLTC3858,ꢀreducingꢀquiescentꢀ
currentꢀtoꢀapproximatelyꢀ8µA.ꢀDoꢀNOTꢀfloatꢀtheseꢀpins.
SW1, SW2 (Pin 25, Pin 16):ꢀSwitchꢀNodeꢀConnectionsꢀ
toꢀInductors.ꢀ
TG1, TG2 (Pin 26, Pin 15):ꢀHighꢀCurrentꢀGateꢀDrivesꢀforꢀ
TopꢀN-ChannelꢀMOSFETs.ꢀTheseꢀareꢀtheꢀoutputsꢀofꢀfloat-
ingꢀdriversꢀwithꢀaꢀvoltageꢀswingꢀequalꢀtoꢀINTV ꢀ–ꢀ0.5Vꢀ
CC
I
(Pin 28):ꢀCurrentꢀComparatorꢀSenseꢀVoltageꢀRangeꢀ
superimposedꢀonꢀtheꢀswitchꢀnodeꢀvoltageꢀSW.
LIM
Inputs.ꢀTyingꢀthisꢀpinꢀtoꢀSGND,ꢀFLOATꢀorꢀINTV ꢀsetsꢀtheꢀ
CC
PGOOD1, PGOOD2 (Pin 27, Pin 14):ꢀOpen-DrainꢀLogicꢀ
maximumꢀcurrentꢀsenseꢀthresholdꢀtoꢀoneꢀofꢀthreeꢀdifferentꢀ
levelsꢀforꢀbothꢀcomparators.
Output.ꢀPGOOD1,2ꢀisꢀpulledꢀtoꢀgroundꢀwhenꢀtheꢀvoltageꢀ
onꢀtheꢀV ꢀpinꢀisꢀnotꢀwithinꢀ 10%ꢀofꢀitsꢀsetꢀpoint.
FB1,2
INTV (Pin19):ꢀOutputꢀofꢀtheꢀInternalꢀLinearꢀLowꢀDropoutꢀ
CC
SS1, SS2 (Pin 29, Pin 13):ꢀExternalꢀSoft-StartꢀInput.ꢀTheꢀ
LTC3858ꢀregulatesꢀtheꢀV ꢀvoltageꢀtoꢀtheꢀsmallerꢀofꢀ0.8Vꢀ
Regulator.ꢀTheꢀdriverꢀandꢀcontrolꢀcircuitsꢀareꢀpoweredꢀ
fromꢀthisꢀvoltageꢀsource.ꢀMustꢀbeꢀdecoupledꢀtoꢀpowerꢀ
groundꢀwithꢀaꢀminimumꢀofꢀ4.7µFꢀceramicꢀorꢀotherꢀlowꢀ
FB1,2
orꢀtheꢀvoltageꢀonꢀtheꢀSS1,2ꢀpin.ꢀAnꢀinternalꢀ1µAꢀpull-upꢀ
currentꢀsourceꢀisꢀconnectedꢀtoꢀthisꢀpin.ꢀAꢀcapacitorꢀtoꢀ
groundꢀatꢀthisꢀpinꢀsetsꢀtheꢀrampꢀtimeꢀtoꢀfinalꢀregulatedꢀ
outputꢀvoltage.ꢀThisꢀpinꢀisꢀalsoꢀusedꢀasꢀtheꢀshort-circuitꢀ
latchoffꢀtimer.
ESRꢀcapacitor.ꢀDoꢀnotꢀuseꢀtheꢀINTV ꢀpinꢀforꢀanyꢀotherꢀ
CC
purpose.
EXTV (Pin 20):ꢀExternalꢀPowerꢀInputꢀtoꢀanꢀInternalꢀLDOꢀ
CC
ConnectedꢀtoꢀINTV .ꢀThisꢀLDOꢀsuppliesꢀINTV ꢀpower,ꢀ
CC
CC
I , I
TH1 TH2
(Pin 30, Pin 12):ꢀErrorꢀAmplifierꢀOutputsꢀandꢀ
bypassingꢀtheꢀinternalꢀLDOꢀpoweredꢀfromꢀV ꢀwheneverꢀ
IN
SwitchingꢀRegulatorꢀCompensationꢀPoints.ꢀEachꢀassoci-
atedꢀchannel’sꢀcurrentꢀcomparatorꢀtripꢀpointꢀincreasesꢀ
withꢀthisꢀcontrolꢀvoltage.
EXTV ꢀisꢀhigherꢀthanꢀ4.7V.ꢀSeeꢀEXTV ꢀConnectionꢀinꢀ
CC
CC
theꢀApplicationsꢀInformationꢀsection.ꢀDoꢀnotꢀexceedꢀ14Vꢀ
onꢀthisꢀpin.
V
, V (Pin31, Pin11):ꢀReceivesꢀtheꢀremotelyꢀsensedꢀ
FB1 FB2
PGND (Pin 21):ꢀDriverꢀPowerꢀGround.ꢀConnectsꢀtoꢀtheꢀ
feedbackꢀ voltageꢀ forꢀ eachꢀ controllerꢀ fromꢀ anꢀ externalꢀ
sourcesꢀofꢀbottomꢀ(synchronous)ꢀN-channelꢀMOSFETsꢀ
resistiveꢀdividerꢀacrossꢀtheꢀoutput.
andꢀtheꢀ(–)ꢀterminal(s)ꢀofꢀC .
IN
+
+
SENSE1 , SENSE2 (Pin 32, Pin 10):ꢀTheꢀ(+)ꢀInputꢀtoꢀ
theꢀ differentialꢀ currentꢀ comparatorsꢀ thatꢀ areꢀ normallyꢀ
connectedꢀtoꢀinductorꢀDCRꢀsensingꢀnetworksꢀorꢀcurrentꢀ
V (Pin 22):ꢀMainꢀInputꢀSupplyꢀPin.ꢀAꢀbypassꢀcapacitorꢀ
IN
shouldꢀbeꢀtiedꢀbetweenꢀthisꢀpinꢀandꢀtheꢀsignalꢀgroundꢀ
pin.
sensingꢀresistors.ꢀTheꢀI ꢀpinꢀvoltageꢀandꢀcontrolledꢀoffsetsꢀ
TH
–
+
BG1, BG2 (Pin 23, Pin 18):ꢀHighꢀCurrentꢀGateꢀDrivesꢀ
betweenꢀtheꢀSENSE ꢀandꢀSENSE ꢀpinsꢀinꢀconjunctionꢀwithꢀ
forꢀBottomꢀ(Synchronous)ꢀN-ChannelꢀMOSFETs.ꢀVoltageꢀ
R
ꢀsetꢀtheꢀcurrentꢀtripꢀthreshold.
SENSE
swingꢀatꢀtheseꢀpinsꢀisꢀfromꢀgroundꢀtoꢀINTV .
CC
BOOST1,BOOST2(Pin24,Pin17):ꢀBootstrappedꢀSuppliesꢀ
toꢀtheꢀTopsideꢀFloatingꢀDrivers.ꢀCapacitorsꢀareꢀconnectedꢀ
betweenꢀtheꢀBOOSTꢀandꢀSWꢀpinsꢀandꢀSchottkyꢀdiodesꢀareꢀ
tiedꢀbetweenꢀtheꢀBOOSTꢀandꢀINTV ꢀpins.ꢀVoltageꢀswingꢀ
CC
atꢀtheꢀBOOSTꢀpinsꢀisꢀfromꢀINTV ꢀtoꢀ(V ꢀ+ꢀINTV ).
CC
IN
CC
3858fa
ꢈ
LTC3858
FuncTional DiagraM
INTV
CC
V
IN
DUPLICATE FOR SECOND
CONTROLLER CHANNEL
BOOST
24, 17
D
+
B
PHASMD
3
CLKOUT
4
PGOOD1
27
0.88V
V
–
TG
26, 15
C
B
FB1
+
–
DROP
OUT
TOP
BOT
C
IN
D
0.72V
0.88V
DET
BOT
SW
25, 16
TOP ON
+
–
S
R
Q
PGOOD2
14
INTV
CC
Q
BG
23, 18
SWITCH
LOGIC
V
FB2
SHDN
+
–
C
OUT
0.72V
PGND
21
20µA
FREQ
2
V
OUT
VCO
CLK2
+
–
R
SENSE
0.425V
SLEEP
CLK1
L
ICMP
IR
–
+
+
–
PFD
C
LP
+
+
–
–
+
SENSE
32, 10
3mV
SYNC
DET
2.7V
0.55V
–
PLLIN/MODE
5
SENSE
1, 9
100k
SLOPE COMP
V
FB
31, 11
I
LIM
R
B
CURRENT
LIMIT
+
28
0.80V
TRACK/SS
EA
–
V
R
A
IN
22
+
–
OV
EXTV
20
CC
I
TH
C
C
0.88V
30, 12
5.1V
LDO
EN
5.1V
LDO
EN
SHDN
RST
FB
C
C2
R
C
0.5µA
11V
FOLDBACK
2(V
)
SS
29, 13
+
–
1µA
4.7V
SHORT CKT
LATCH-OFF
C
SHDN
10µA
SS
RUN
7, 8
6
SGND
19 INTV
CC
3858 FD
3858fa
ꢀ0
LTC3858
operaTion (Refer to the Functional Diagram)
TheꢀLTC3858ꢀusesꢀaꢀconstantꢀfrequency,ꢀcurrentꢀmodeꢀ Shutdown and Start-Up (RUN1, RUN2
step-downꢀarchitectureꢀwithꢀtheꢀtwoꢀcontrollerꢀchannelsꢀ and SS1, SS2 Pins)
operatingꢀ180ꢀdegreesꢀoutꢀofꢀphase.ꢀDuringꢀnormalꢀop-
TheꢀtwoꢀchannelsꢀofꢀtheꢀLTC3858ꢀcanꢀbeꢀindependentlyꢀ
shutꢀdownꢀusingꢀtheꢀRUN1ꢀandꢀRUN2ꢀpins.ꢀPullingꢀeitherꢀofꢀ
theseꢀpinsꢀbelowꢀ1.26Vꢀshutsꢀdownꢀtheꢀmainꢀcontrolꢀloopꢀ
forꢀthatꢀcontroller.ꢀPullingꢀbothꢀpinsꢀbelowꢀ0.7Vꢀdisablesꢀ
bothꢀcontrollersꢀandꢀmostꢀinternalꢀcircuits,ꢀincludingꢀtheꢀ
eration,ꢀeachꢀexternalꢀtopꢀMOSFETꢀisꢀturnedꢀonꢀwhenꢀtheꢀ
clockꢀforꢀthatꢀchannelꢀsetsꢀtheꢀRSꢀlatch,ꢀandꢀisꢀturnedꢀoffꢀ
whenꢀtheꢀmainꢀcurrentꢀcomparator,ꢀICMP,ꢀresetsꢀtheꢀRSꢀ
latch.ꢀTheꢀpeakꢀinductorꢀcurrentꢀatꢀwhichꢀICMPꢀtripsꢀandꢀ
resetsꢀtheꢀlatchꢀisꢀcontrolledꢀbyꢀtheꢀvoltageꢀonꢀtheꢀI ꢀpin,ꢀ
TH
INTV ꢀLDOs.ꢀInꢀthisꢀstate,ꢀtheꢀLTC3858ꢀdrawsꢀonlyꢀ8µAꢀ
CC
whichꢀisꢀtheꢀoutputꢀofꢀtheꢀerrorꢀamplifier,ꢀEA.ꢀTheꢀerrorꢀ
ofꢀquiescentꢀcurrent.
amplifierꢀcomparesꢀtheꢀoutputꢀvoltageꢀfeedbackꢀsignalꢀatꢀ
TheꢀRUNꢀpinꢀmayꢀbeꢀexternallyꢀpulledꢀupꢀorꢀdrivenꢀdirectlyꢀ
byꢀlogic.ꢀWhenꢀdrivingꢀtheꢀRUNꢀpinꢀwithꢀaꢀlowꢀimpedanceꢀ
source,ꢀdoꢀnotꢀexceedꢀtheꢀabsoluteꢀmaximumꢀratingꢀofꢀ
8V.ꢀTheꢀRUNꢀpinꢀhasꢀanꢀinternalꢀ11Vꢀvoltageꢀclampꢀthatꢀ
allowsꢀtheꢀRUNꢀpinꢀtoꢀbeꢀconnectedꢀthroughꢀaꢀresistorꢀtoꢀaꢀ
theꢀV ꢀpinꢀ(whichꢀisꢀgeneratedꢀwithꢀanꢀexternalꢀresistorꢀ
FB
dividerꢀ connectedꢀ acrossꢀ theꢀ outputꢀ voltage,ꢀ V ,ꢀ toꢀ
OUTꢀ
ground)ꢀtoꢀtheꢀinternalꢀ0.800Vꢀreferenceꢀvoltage.ꢀWhenꢀtheꢀ
loadꢀcurrentꢀincreases,ꢀitꢀcausesꢀaꢀslightꢀdecreaseꢀinꢀV ꢀ
FB
relativeꢀtoꢀtheꢀreference,ꢀwhichꢀcausesꢀtheꢀEAꢀtoꢀincreaseꢀ
higherꢀvoltageꢀ(forꢀexample,ꢀV ),ꢀsoꢀlongꢀasꢀtheꢀmaximumꢀ
theꢀI ꢀvoltageꢀuntilꢀtheꢀaverageꢀinductorꢀcurrentꢀmatchesꢀ
IN
TH
currentꢀintoꢀtheꢀRUNꢀpinꢀdoesꢀnotꢀexceedꢀ100µA.
theꢀnewꢀloadꢀcurrent.
Theꢀstart-upꢀofꢀeachꢀcontroller’sꢀoutputꢀvoltage,ꢀV ,ꢀisꢀ
AfterꢀtheꢀtopꢀMOSFETꢀisꢀturnedꢀoffꢀeachꢀcycle,ꢀtheꢀbottomꢀ
MOSFETꢀisꢀturnedꢀonꢀuntilꢀeitherꢀtheꢀinductorꢀcurrentꢀstartsꢀ
toꢀreverse,ꢀasꢀindicatedꢀbyꢀtheꢀcurrentꢀcomparatorꢀIR,ꢀorꢀ
theꢀbeginningꢀofꢀtheꢀnextꢀclockꢀcycle.
OUTꢀ
controlledꢀbyꢀtheꢀvoltageꢀonꢀtheꢀSSꢀpinꢀforꢀthatꢀchannel.ꢀ
WhenꢀtheꢀvoltageꢀonꢀtheꢀSSꢀpinꢀisꢀlessꢀthanꢀtheꢀ0.8Vꢀinternalꢀ
reference,ꢀtheꢀLTC3858ꢀregulatesꢀtheꢀV ꢀvoltageꢀtoꢀtheꢀSSꢀ
FB
pinꢀvoltageꢀinsteadꢀofꢀtheꢀ0.8Vꢀreference.ꢀThisꢀallowsꢀtheꢀ
SSꢀpinꢀtoꢀbeꢀusedꢀtoꢀprogramꢀaꢀsoft-startꢀbyꢀconnectingꢀ
anꢀexternalꢀcapacitorꢀfromꢀtheꢀSSꢀpinꢀtoꢀSGND.ꢀAnꢀinternalꢀ
1µAꢀpull-upꢀcurrentꢀchargesꢀthisꢀcapacitorꢀcreatingꢀaꢀvolt-
ageꢀrampꢀonꢀtheꢀSSꢀpin.ꢀAsꢀtheꢀSSꢀvoltageꢀrisesꢀlinearlyꢀ
fromꢀ0Vꢀtoꢀ0.8Vꢀ(andꢀbeyondꢀupꢀtoꢀtheꢀabsoluteꢀmaximumꢀ
INTV /EXTV Power
CC
CC
PowerꢀforꢀtheꢀtopꢀandꢀbottomꢀMOSFETꢀdriversꢀandꢀmostꢀ
otherꢀinternalꢀcircuitryꢀisꢀderivedꢀfromꢀtheꢀINTV ꢀpin.ꢀWhenꢀ
CC
theꢀEXTV ꢀpinꢀisꢀleftꢀopenꢀorꢀtiedꢀtoꢀaꢀvoltageꢀlessꢀthanꢀ
CC
4.7V,ꢀtheꢀV ꢀLDOꢀ(lowꢀdropoutꢀlinearꢀregulator)ꢀsuppliesꢀ
IN
ratingꢀofꢀ6V),ꢀtheꢀoutputꢀvoltageꢀV ꢀrisesꢀsmoothlyꢀfromꢀ
OUT
5.1VꢀfromꢀV ꢀtoꢀINTV .ꢀIfꢀEXTV ꢀisꢀtakenꢀaboveꢀ4.7V,ꢀ
IN
CC
CC
zeroꢀtoꢀitsꢀfinalꢀvalue.
theꢀV ꢀLDOꢀisꢀturnedꢀoffꢀandꢀtheꢀEXTV ꢀLDOꢀisꢀturnedꢀon.ꢀ
IN
CC
Onceꢀenabled,ꢀtheꢀEXTV ꢀLDOꢀsuppliesꢀ5.1VꢀfromꢀEXTV ꢀ
CC
CC
Short-Circuit Latch-Off
toꢀINTV .ꢀUsingꢀtheꢀEXTV ꢀpinꢀallowsꢀtheꢀINTV ꢀpowerꢀ
CC
CC
CC
Afterꢀ theꢀ controllerꢀ hasꢀ beenꢀ startedꢀ andꢀ beenꢀ givenꢀ
adequateꢀ timeꢀ toꢀ rampꢀ upꢀ theꢀ outputꢀ voltage,ꢀ theꢀ SSꢀ
capacitorꢀisꢀusedꢀinꢀaꢀshort-circuitꢀtime-outꢀcircuit.ꢀSpe-
cifically,ꢀonceꢀtheꢀvoltageꢀonꢀtheꢀSSꢀpinꢀrisesꢀaboveꢀ2Vꢀ
(theꢀarmingꢀthreshold),ꢀtheꢀshort-circuitꢀtimeoutꢀcircuitꢀisꢀ
enabledꢀ(seeꢀFigureꢀ1).ꢀIfꢀtheꢀoutputꢀvoltageꢀfallsꢀbelowꢀ
70%ꢀofꢀitsꢀnominalꢀregulatedꢀvoltage,ꢀtheꢀSSꢀcapacitorꢀ
beginsꢀdischargingꢀwithꢀaꢀnetꢀ9µAꢀpull-downꢀcurrentꢀonꢀ
theꢀassumptionꢀthatꢀtheꢀoutputꢀisꢀinꢀanꢀovercurrentꢀand/orꢀ
short-circuitꢀcondition.ꢀIfꢀtheꢀconditionꢀlastsꢀlongꢀenoughꢀ
toꢀbeꢀderivedꢀfromꢀaꢀhighꢀefficiencyꢀexternalꢀsourceꢀsuchꢀ
asꢀoneꢀofꢀtheꢀLTC3858ꢀswitchingꢀregulatorꢀoutputs.
EachꢀtopꢀMOSFETꢀdriverꢀisꢀbiasedꢀfromꢀtheꢀfloatingꢀboot-
strapꢀcapacitor,ꢀC ,ꢀwhichꢀnormallyꢀrechargesꢀduringꢀeachꢀ
B
switchingꢀcycleꢀthroughꢀanꢀexternalꢀdiodeꢀwhenꢀtheꢀtopꢀ
MOSFETꢀturnsꢀoff.ꢀIfꢀtheꢀinputꢀvoltage,ꢀV ,ꢀdecreasesꢀtoꢀ
IN
aꢀvoltageꢀcloseꢀtoꢀV ,ꢀtheꢀloopꢀmayꢀenterꢀdropoutꢀandꢀ
OUTꢀ
attemptꢀtoꢀturnꢀonꢀtheꢀtopꢀMOSFETꢀcontinuously.ꢀTheꢀ
dropoutꢀdetectorꢀdetectsꢀthisꢀandꢀforcesꢀtheꢀtopꢀMOSFETꢀ
offꢀforꢀaboutꢀone-twelfthꢀofꢀtheꢀclockꢀperiodꢀeveryꢀtenthꢀ
cycleꢀtoꢀallowꢀC ꢀtoꢀrecharge.
B
3858fa
ꢀꢀ
LTC3858
operaTion (Refer to the Functional Diagram)
INTV
CC
limitꢀinꢀproportionꢀtoꢀtheꢀseverityꢀofꢀtheꢀovercurrentꢀorꢀ
short-circuitꢀcondition.ꢀEvenꢀifꢀaꢀshortꢀcircuitꢀisꢀpresentꢀ
andꢀ theꢀ short-circuitꢀ latch-offꢀ isꢀ notꢀ yetꢀ armedꢀ (whenꢀ
SSꢀvoltageꢀhasꢀnotꢀyetꢀreachedꢀ2V),ꢀaꢀsafe,ꢀlowꢀoutputꢀ
currentꢀisꢀprovidedꢀdueꢀtoꢀinternalꢀcurrentꢀfoldbackꢀandꢀ
actualꢀpowerꢀwastedꢀisꢀlowꢀdueꢀtoꢀtheꢀefficientꢀnatureꢀofꢀ
theꢀcurrentꢀmodeꢀswitchingꢀregulator.ꢀFoldbackꢀcurrentꢀ
limitingꢀisꢀdisabledꢀduringꢀtheꢀsoft-startꢀintervalꢀ(asꢀlongꢀ
SS VOLTAGE
2V
1.5V
0.8V
LATCH-OFF
COMMAND
0V
SS PIN
CURRENT
1µA
1µA
–9µA
asꢀtheꢀV ꢀvoltageꢀisꢀkeepingꢀupꢀwithꢀtheꢀSSꢀvoltage).ꢀ
FB
OUTPUT
VOLTAGE
Light Load Current Operation (Burst Mode Operation,
Pulse-Skipping or Forced Continuous)
(PLLIN/MODE Pin)
3858 F01
LATCH-OFF
ENABLE
ARMING
SOFT-START INTERVAL
t
LATCH
TheꢀLTC3858ꢀcanꢀbeꢀenabledꢀtoꢀenterꢀhighꢀefficiencyꢀ
BurstꢀModeꢀoperation,ꢀconstantꢀfrequencyꢀpulse-skip-
pingꢀmode,ꢀorꢀforcedꢀcontinuousꢀconductionꢀmodeꢀatꢀ
lowꢀloadꢀcurrents.ꢀToꢀselectꢀBurstꢀModeꢀoperation,ꢀtieꢀtheꢀ
PLLIN/ꢀMODEꢀpinꢀtoꢀground.ꢀToꢀselectꢀforcedꢀcontinuousꢀ
Figure 1. Latch-Off Timing Diagram
toꢀallowꢀtheꢀSSꢀpinꢀvoltageꢀtoꢀfallꢀbelowꢀ1.5Vꢀ(theꢀlatchoffꢀ
threshold),ꢀtheꢀcontrollerꢀwillꢀshutꢀdownꢀ(latchꢀoff)ꢀuntilꢀ
operation,ꢀtieꢀtheꢀPLLIN/MODEꢀpinꢀtoꢀINTV .ꢀToꢀselectꢀ
CC
theꢀRUNꢀpinꢀvoltageꢀorꢀtheꢀV ꢀvoltageꢀisꢀrecycled.
IN
pulse-skippingꢀmode,ꢀtieꢀtheꢀPLLIN/MODEꢀpinꢀtoꢀaꢀDCꢀ
Theꢀdelayꢀtimeꢀfromꢀwhenꢀaꢀshort-circuitꢀoccursꢀuntilꢀtheꢀ
controllerꢀlatchesꢀoffꢀcanꢀbeꢀcalculatedꢀusingꢀtheꢀfollow-
ingꢀequation
voltageꢀgreaterꢀthanꢀ1.2VꢀandꢀlessꢀthanꢀINTV ꢀ–ꢀ1.3V.
CC
WhenꢀaꢀcontrollerꢀisꢀenabledꢀforꢀBurstꢀModeꢀoperation,ꢀtheꢀ
minimumꢀpeakꢀcurrentꢀinꢀtheꢀinductorꢀisꢀsetꢀtoꢀapproxi-
matelyꢀ30%ꢀofꢀtheꢀmaximumꢀsenseꢀvoltageꢀevenꢀthoughꢀ
VSS – 1.5V
tLATCH ≈ CSS
9µA
theꢀvoltageꢀonꢀtheꢀI ꢀpinꢀindicatesꢀaꢀlowerꢀvalue.ꢀIfꢀtheꢀ
TH
ꢀ
averageꢀinductorꢀcurrentꢀisꢀhigherꢀthanꢀtheꢀloadꢀcurrent,ꢀ
whereꢀV ꢀisꢀtheꢀinitialꢀvoltageꢀ(mustꢀbeꢀgreaterꢀthanꢀ2V)ꢀ
SS
theꢀerrorꢀamplifierꢀEAꢀwillꢀdecreaseꢀtheꢀvoltageꢀonꢀtheꢀI ꢀ
TH
onꢀtheꢀSSꢀpinꢀatꢀtheꢀtimeꢀtheꢀshort-circuitꢀoccurs.ꢀNormallyꢀ
pin.ꢀWhenꢀtheꢀI ꢀvoltageꢀdropsꢀbelowꢀ0.425V,ꢀtheꢀinternalꢀ
TH
theꢀSSꢀpinꢀvoltageꢀwillꢀhaveꢀbeenꢀpulledꢀupꢀtoꢀtheꢀINTV ꢀ
CC
sleepꢀsignalꢀgoesꢀhighꢀ(enablingꢀ“sleep”ꢀmode)ꢀandꢀbothꢀ
voltageꢀ(5.1V)ꢀbyꢀtheꢀinternalꢀ1µAꢀpull-upꢀcurrent.
externalꢀMOSFETsꢀareꢀturnedꢀoff.ꢀ
NoteꢀthatꢀtheꢀtwoꢀcontrollersꢀonꢀtheꢀLTC3858ꢀhaveꢀseparate,ꢀ
independentꢀshort-circuitꢀlatchoffꢀcircuits.ꢀLatchoffꢀcanꢀbeꢀ
overridden/defeatedꢀbyꢀconnectingꢀaꢀresistorꢀ150kꢀorꢀlessꢀ
Inꢀsleepꢀmode,ꢀmuchꢀofꢀtheꢀinternalꢀcircuitryꢀisꢀturnedꢀoff,ꢀ
reducingꢀtheꢀquiescentꢀcurrent.ꢀIfꢀoneꢀchannelꢀisꢀshutꢀdownꢀ
andꢀtheꢀotherꢀchannelꢀisꢀinꢀsleepꢀmode,ꢀtheꢀLTC3858ꢀdrawsꢀ
onlyꢀ170µAꢀofꢀquiescentꢀcurrent.ꢀIfꢀbothꢀchannelsꢀareꢀinꢀ
sleepꢀmode,ꢀtheꢀLTC3858ꢀdrawsꢀonlyꢀ300µAꢀofꢀquiescentꢀ
current.ꢀInꢀsleepꢀmode,ꢀtheꢀloadꢀcurrentꢀisꢀsuppliedꢀbyꢀ
theꢀoutputꢀcapacitor.ꢀAsꢀtheꢀoutputꢀvoltageꢀdecreases,ꢀtheꢀ
EA’sꢀoutputꢀbeginsꢀtoꢀrise.ꢀWhenꢀtheꢀoutputꢀvoltageꢀdropsꢀ
fromꢀtheꢀSSꢀpinꢀtoꢀINTV .ꢀThisꢀresistorꢀprovidesꢀenoughꢀ
CC
pull-upꢀcurrentꢀtoꢀovercomeꢀtheꢀ9µAꢀpull-downꢀcurrentꢀ
presentꢀduringꢀaꢀshort-circuit.ꢀNoteꢀthatꢀthisꢀresistorꢀalsoꢀ
shortensꢀtheꢀsoft-startꢀperiod.
Foldback Current
enough,ꢀtheꢀI ꢀpinꢀisꢀreconnectedꢀtoꢀtheꢀoutputꢀofꢀtheꢀ
TH
EA,ꢀtheꢀsleepꢀsignalꢀgoesꢀlow,ꢀandꢀtheꢀcontrollerꢀresumesꢀ
normalꢀoperationꢀbyꢀturningꢀonꢀtheꢀtopꢀexternalꢀMOSFETꢀ
onꢀtheꢀnextꢀcycleꢀofꢀtheꢀinternalꢀoscillator.
Onꢀtheꢀotherꢀhand,ꢀwhenꢀtheꢀoutputꢀvoltageꢀfallsꢀtoꢀlessꢀ
thanꢀ70%ꢀofꢀitsꢀnominalꢀlevel,ꢀfoldbackꢀcurrentꢀlimitingꢀ
isꢀalsoꢀactivated,ꢀprogressivelyꢀloweringꢀtheꢀpeakꢀcurrentꢀ
3858fa
ꢀꢁ
LTC3858
operaTion (Refer to the Functional Diagram)
IfꢀtheꢀPLLIN/MODEꢀpinꢀisꢀnotꢀbeingꢀdrivenꢀbyꢀanꢀexternalꢀ
clockꢀsource,ꢀtheꢀFREQꢀpinꢀcanꢀbeꢀtiedꢀtoꢀSGND,ꢀtiedꢀtoꢀ
WhenꢀaꢀcontrollerꢀisꢀenabledꢀforꢀBurstꢀModeꢀoperation,ꢀ
theꢀinductorꢀcurrentꢀisꢀnotꢀallowedꢀtoꢀreverse.ꢀTheꢀreverseꢀ
currentꢀ comparator,ꢀ IR,ꢀ turnsꢀ offꢀ theꢀ bottomꢀ externalꢀ
MOSFETꢀjustꢀbeforeꢀtheꢀinductorꢀcurrentꢀreachesꢀzero,ꢀ
preventingꢀitꢀfromꢀreversingꢀandꢀgoingꢀnegative.ꢀThus,ꢀ
theꢀcontrollerꢀisꢀinꢀdiscontinuousꢀoperation.
INTV ꢀorꢀprogrammedꢀthroughꢀanꢀexternalꢀresistor.ꢀTyingꢀ
CC
FREQꢀtoꢀSGNDꢀselectsꢀ350kHzꢀwhileꢀtyingꢀFREQꢀtoꢀINTV ꢀ
CC
selectsꢀ535kHz.ꢀPlacingꢀaꢀresistorꢀbetweenꢀFREQꢀandꢀSGNDꢀ
allowsꢀtheꢀfrequencyꢀtoꢀbeꢀprogrammedꢀbetweenꢀ50kHzꢀ
andꢀ900kHz,ꢀasꢀshownꢀinꢀFigureꢀ9
Inꢀforcedꢀcontinuousꢀoperationꢀorꢀwhenꢀclockedꢀbyꢀanꢀ
externalꢀclockꢀsourceꢀtoꢀuseꢀtheꢀphase-lockedꢀloopꢀ(seeꢀ
FrequencyꢀSelectionꢀandꢀPhase-LockedꢀLoopꢀsection),ꢀ
theꢀinductorꢀcurrentꢀisꢀallowedꢀtoꢀreverseꢀatꢀlightꢀloadsꢀ
orꢀunderꢀlargeꢀtransientꢀconditions.ꢀTheꢀpeakꢀinductorꢀ
Aꢀphase-lockedꢀloopꢀ(PLL)ꢀisꢀavailableꢀonꢀtheꢀLTC3858ꢀ
toꢀsynchronizeꢀtheꢀinternalꢀoscillatorꢀtoꢀanꢀexternalꢀclockꢀ
sourceꢀthatꢀisꢀconnectedꢀtoꢀtheꢀPLLIN/MODEꢀpin.ꢀTheꢀ
phaseꢀdetectorꢀadjustsꢀtheꢀvoltageꢀ(throughꢀanꢀinternalꢀ
lowpassꢀfilter)ꢀofꢀtheꢀVCOꢀinputꢀtoꢀalignꢀtheꢀturn-onꢀofꢀ
controllerꢀ1’sꢀexternalꢀtopꢀMOSFETꢀtoꢀtheꢀrisingꢀedgeꢀofꢀ
theꢀsynchronizingꢀsignal.ꢀThus,ꢀtheꢀturn-onꢀofꢀcontrollerꢀ2’sꢀ
externalꢀtopꢀMOSFETꢀisꢀ180ꢀdegreesꢀoutꢀofꢀphaseꢀtoꢀtheꢀ
risingꢀedgeꢀofꢀtheꢀexternalꢀclockꢀsource.
currentꢀisꢀdeterminedꢀbyꢀtheꢀvoltageꢀonꢀtheꢀI ꢀpin,ꢀjustꢀ
TH
asꢀinꢀnormalꢀoperation.ꢀInꢀthisꢀmode,ꢀtheꢀefficiencyꢀatꢀlightꢀ
loadsꢀisꢀlowerꢀthanꢀinꢀBurstꢀModeꢀoperation.ꢀHowever,ꢀ
continuousꢀoperationꢀhasꢀtheꢀadvantagesꢀofꢀlowerꢀoutputꢀ
voltageꢀrippleꢀandꢀlessꢀinterferenceꢀtoꢀaudioꢀcircuitry.ꢀInꢀ
forcedꢀcontinuousꢀmode,ꢀtheꢀoutputꢀrippleꢀisꢀindependentꢀ
ofꢀloadꢀcurrent.
Theꢀ VCOꢀ inputꢀ voltageꢀ isꢀ pre-biasedꢀ toꢀ theꢀ operatingꢀ
frequencyꢀsetꢀbyꢀtheꢀFREQꢀpinꢀbeforeꢀtheꢀexternalꢀclockꢀ
isꢀapplied.ꢀIfꢀprebiasedꢀnearꢀtheꢀexternalꢀclockꢀfrequency,ꢀ
theꢀPLLꢀloopꢀonlyꢀneedsꢀtoꢀmakeꢀslightꢀchangesꢀtoꢀtheꢀ
VCOꢀinputꢀinꢀorderꢀtoꢀsynchronizeꢀtheꢀrisingꢀedgeꢀofꢀtheꢀ
externalꢀclock’sꢀtoꢀtheꢀrisingꢀedgeꢀofꢀTG1.ꢀTheꢀabilityꢀtoꢀ
pre-biasꢀtheꢀloopꢀfilterꢀallowsꢀtheꢀPLLꢀtoꢀlock-inꢀrapidlyꢀ
withoutꢀdeviatingꢀfarꢀfromꢀtheꢀdesiredꢀfrequency.
WhenꢀtheꢀPLLIN/MODEꢀpinꢀisꢀconnectedꢀforꢀpulse-skip-
pingꢀmode,ꢀtheꢀLTC3858ꢀoperatesꢀinꢀPWMꢀpulse-skippingꢀ
modeꢀatꢀlightꢀloads.ꢀInꢀthisꢀmode,ꢀconstantꢀfrequencyꢀ
operationꢀisꢀmaintainedꢀdownꢀtoꢀapproximatelyꢀ1%ꢀofꢀ
designedꢀmaximumꢀoutputꢀcurrent.ꢀAtꢀveryꢀlightꢀloads,ꢀtheꢀ
currentꢀcomparator,ꢀICMP,ꢀmayꢀremainꢀtrippedꢀforꢀseveralꢀ
cyclesꢀandꢀforceꢀtheꢀexternalꢀtopꢀMOSFETꢀtoꢀstayꢀoffꢀforꢀ
theꢀsameꢀnumberꢀofꢀcyclesꢀ(i.e.,ꢀskippingꢀpulses).ꢀTheꢀ
inductorꢀcurrentꢀisꢀnotꢀallowedꢀtoꢀreverseꢀ(discontinuousꢀ
operation).ꢀThisꢀmode,ꢀlikeꢀforcedꢀcontinuousꢀoperation,ꢀ
exhibitsꢀlowꢀoutputꢀrippleꢀasꢀwellꢀasꢀlowꢀaudioꢀnoiseꢀandꢀ
reducedꢀRFꢀinterferenceꢀwhenꢀcomparedꢀtoꢀBurstꢀModeꢀ
operation.ꢀ Itꢀ providesꢀ higherꢀ lightꢀ loadꢀ efficiencyꢀ thanꢀ
forcedꢀcontinuousꢀmode,ꢀbutꢀnotꢀnearlyꢀasꢀhighꢀasꢀBurstꢀ
Modeꢀoperation.
Theꢀtypicalꢀcaptureꢀrangeꢀofꢀtheꢀphase-lockedꢀloopꢀisꢀfromꢀ
approximatelyꢀ55kHzꢀtoꢀ1MHz,ꢀwithꢀaꢀguaranteeꢀoverꢀallꢀ
manufacturingꢀvariationsꢀtoꢀbeꢀbetweenꢀ75kHzꢀandꢀ850kHz.ꢀ
Inꢀotherꢀwords,ꢀtheꢀLTC3858’sꢀPLLꢀisꢀguaranteedꢀtoꢀlockꢀ
toꢀanꢀexternalꢀclockꢀsourceꢀwhoseꢀfrequencyꢀisꢀbetweenꢀ
75kHzꢀandꢀ850kHz.
TheꢀtypicalꢀinputꢀclockꢀthresholdsꢀonꢀtheꢀPLLIN/MODEꢀ
pinꢀareꢀ1.6Vꢀ(rising)ꢀandꢀ1.1Vꢀ(falling).
PolyPhase® Applications (CLKOUT and PHASMD Pins)
Frequency Selection and Phase-Locked Loop
(FREQ and PLLIN/MODE Pins)
TheꢀLTC3858ꢀfeaturesꢀtwoꢀpinsꢀ(CLKOUTꢀandꢀPHASMD)ꢀ
thatꢀallowꢀotherꢀcontrollerꢀICsꢀtoꢀbeꢀdaisy-chainedꢀwithꢀ
theꢀLTC3858ꢀinꢀPolyPhaseꢀapplications.ꢀTheꢀclockꢀoutputꢀ
signalꢀonꢀtheꢀCLKOUTꢀpinꢀcanꢀbeꢀusedꢀtoꢀsynchronizeꢀ
additionalꢀpowerꢀstagesꢀinꢀaꢀmultiphaseꢀpowerꢀsupplyꢀ
solutionꢀfeedingꢀaꢀsingle,ꢀhighꢀcurrentꢀoutputꢀorꢀmultipleꢀ
separateꢀoutputs.ꢀTheꢀPHASMDꢀpinꢀisꢀusedꢀtoꢀadjustꢀtheꢀ
phaseꢀofꢀtheꢀCLKOUTꢀsignalꢀasꢀwellꢀasꢀtheꢀrelativeꢀphasesꢀ
Theꢀselectionꢀofꢀswitchingꢀfrequencyꢀisꢀaꢀtradeoffꢀbetweenꢀ
efficiencyꢀ andꢀ componentꢀ size.ꢀ Lowꢀ frequencyꢀ opera-
tionꢀincreasesꢀefficiencyꢀbyꢀreducingꢀMOSFETꢀswitchingꢀ
losses,ꢀbutꢀrequiresꢀlargerꢀinductanceꢀand/orꢀcapacitanceꢀ
toꢀmaintainꢀlowꢀoutputꢀrippleꢀvoltage.
TheꢀswitchingꢀfrequencyꢀofꢀtheꢀLTC3858’sꢀcontrollersꢀcanꢀ
beꢀselectedꢀusingꢀtheꢀFREQꢀpin.
3858fa
ꢀꢂ
LTC3858
operaTion (Refer to the Functional Diagram)
Theory and Benefits of 2-Phase Operation
betweenꢀtheꢀtwoꢀinternalꢀcontrollers,ꢀasꢀsummarizedꢀinꢀ
Tableꢀ1.ꢀTheꢀphasesꢀareꢀcalculatedꢀrelativeꢀtoꢀtheꢀzeroꢀ
degreesꢀphaseꢀbeingꢀdefinedꢀasꢀtheꢀrisingꢀedgeꢀofꢀtheꢀtopꢀ
gateꢀdriverꢀoutputꢀofꢀcontrollerꢀ1ꢀ(TG1).
Whyꢀtheꢀneedꢀforꢀ2-phaseꢀoperation?ꢀUpꢀuntilꢀtheꢀ2-phaseꢀ
family,ꢀ constantꢀ frequencyꢀ dualꢀ switchingꢀ regulatorsꢀ
operatedꢀ bothꢀ channelsꢀ inꢀ phaseꢀ (i.e.,ꢀ singleꢀ phaseꢀ
operation).ꢀThisꢀmeansꢀthatꢀbothꢀswitchesꢀturnedꢀonꢀatꢀ
theꢀsameꢀtime,ꢀcausingꢀcurrentꢀpulsesꢀofꢀupꢀtoꢀtwiceꢀtheꢀ
amplitudeꢀofꢀthoseꢀforꢀoneꢀregulatorꢀtoꢀbeꢀdrawnꢀfromꢀtheꢀ
inputꢀcapacitorꢀandꢀbattery.ꢀTheseꢀlargeꢀamplitudeꢀcurrentꢀ
pulsesꢀincreasedꢀtheꢀtotalꢀRMSꢀcurrentꢀflowingꢀfromꢀtheꢀ
inputꢀcapacitor,ꢀrequiringꢀtheꢀuseꢀofꢀmoreꢀexpensiveꢀinputꢀ
capacitorsꢀandꢀincreasingꢀbothꢀEMIꢀandꢀlossesꢀinꢀtheꢀinputꢀ
capacitorꢀandꢀbattery.
Table 1
V
CONTROLLER 2 PHASE
CLKOUT PHASE
PHASMD
GND
180°
180°
240°
60°
90°
Floating
INTV
120°
CC
Output Overvoltage Protection
Anꢀovervoltageꢀcomparatorꢀguardsꢀagainstꢀtransientꢀover-
shootsꢀasꢀwellꢀasꢀotherꢀmoreꢀseriousꢀconditionsꢀthatꢀmayꢀ
Withꢀ 2-phaseꢀ operation,ꢀ theꢀ twoꢀ channelsꢀ ofꢀ theꢀ dualꢀ
switchingꢀregulatorꢀareꢀoperatedꢀ180ꢀdegreesꢀoutꢀofꢀphase.ꢀ
Thisꢀeffectivelyꢀinterleavesꢀtheꢀcurrentꢀpulsesꢀdrawnꢀbyꢀtheꢀ
switches,ꢀgreatlyꢀreducingꢀtheꢀoverlapꢀtimeꢀwhereꢀtheyꢀaddꢀ
together.ꢀTheꢀresultꢀisꢀaꢀsignificantꢀreductionꢀinꢀtotalꢀRMSꢀ
inputꢀcurrent,ꢀwhichꢀinꢀturnꢀallowsꢀlessꢀexpensiveꢀinputꢀ
capacitorsꢀtoꢀbeꢀused,ꢀreducesꢀshieldingꢀrequirementsꢀforꢀ
EMIꢀandꢀimprovesꢀrealꢀworldꢀoperatingꢀefficiency.
overvoltageꢀtheꢀoutput.ꢀWhenꢀtheꢀV ꢀpinꢀrisesꢀbyꢀmoreꢀ
FB
thanꢀ10%ꢀaboveꢀitsꢀregulationꢀpointꢀofꢀ0.800V,ꢀtheꢀtopꢀ
MOSFETꢀisꢀturnedꢀoffꢀandꢀtheꢀbottomꢀMOSFETꢀisꢀturnedꢀ
onꢀuntilꢀtheꢀovervoltageꢀconditionꢀisꢀcleared.
Power Good (PGOOD1 and PGOOD2) Pins
EachꢀPGOODꢀpinꢀisꢀconnectedꢀtoꢀanꢀopenꢀdrainꢀofꢀanꢀ
internalꢀN-channelꢀMOSFET.ꢀTheꢀMOSFETꢀturnsꢀonꢀandꢀ
Figureꢀ2ꢀcomparesꢀtheꢀinputꢀwaveformsꢀforꢀaꢀrepresenta-
tiveꢀsingle-phaseꢀdualꢀswitchingꢀregulatorꢀtoꢀtheꢀLTC3858ꢀ
2-phaseꢀdualꢀswitchingꢀregulator.ꢀAnꢀactualꢀmeasurementꢀofꢀ
theꢀRMSꢀinputꢀcurrentꢀunderꢀtheseꢀconditionsꢀshowsꢀthatꢀ
pullsꢀtheꢀPGOODꢀpinꢀlowꢀwhenꢀtheꢀcorrespondingꢀV ꢀpinꢀ
FB
voltageꢀisꢀnotꢀwithinꢀ 10%ꢀofꢀtheꢀ0.8Vꢀreferenceꢀvoltage.ꢀ
TheꢀPGOODꢀpinꢀisꢀalsoꢀpulledꢀlowꢀwhenꢀtheꢀcorrespondingꢀ
2-phaseꢀoperationꢀdroppedꢀtheꢀinputꢀcurrentꢀfromꢀ2.53A
ꢀ
RUNꢀpinꢀisꢀlowꢀ(shutꢀdown).ꢀWhenꢀtheꢀV ꢀpinꢀvoltageꢀ
RMS
FB
toꢀ1.55A
.ꢀWhileꢀthisꢀisꢀanꢀimpressiveꢀreductionꢀinꢀitself,ꢀ
isꢀwithinꢀtheꢀ 10%ꢀrequirement,ꢀtheꢀMOSFETꢀisꢀturnedꢀ
offꢀandꢀtheꢀpinꢀisꢀallowedꢀtoꢀbeꢀpulledꢀupꢀbyꢀanꢀexternalꢀ
resistorꢀtoꢀaꢀsourceꢀnoꢀgreaterꢀthanꢀ6V.
RMS
2
rememberꢀthatꢀtheꢀpowerꢀlossesꢀareꢀproportionalꢀtoꢀI
,ꢀ
RMS
meaningꢀthatꢀtheꢀactualꢀpowerꢀwastedꢀisꢀreducedꢀbyꢀaꢀ
5V SWITCH
20V/DIV
3.3V SWITCH
20V/DIV
INPUT CURRENT
5A/DIV
INPUT VOLTAGE
500mV/DIV
3858 F02
I
= 2.53A
I
= 1.55A
IN(MEAS) RMS
IN(MEAS)
RMS
Figure 2. Input Waveforms Comparing Single-Phase (a) and 2-Phase (b) Operation for Dual Switching Regulators
Converting 12V to 5V and 3.3V at 3A Each. The Reduced Input Ripple with the 2-Phase Regulator Allows
Less Expensive Input Capacitors, Reduces Shielding Requirements for EMI and Improves Efficiency
3858fa
ꢀꢃ
LTC3858
operaTion (Refer to the Functional Diagram)
factorꢀofꢀ2.66.ꢀTheꢀreducedꢀinputꢀrippleꢀvoltageꢀalsoꢀmeansꢀ voltageꢀV ꢀ(DutyꢀCycleꢀ=ꢀV /V ).ꢀFigureꢀ3ꢀshowsꢀhowꢀ
IN
OUT IN
lessꢀpowerꢀisꢀlostꢀinꢀtheꢀinputꢀpowerꢀpath,ꢀwhichꢀcouldꢀ theꢀRMSꢀinputꢀcurrentꢀvariesꢀforꢀsingleꢀphaseꢀandꢀ2-phaseꢀ
includeꢀbatteries,ꢀswitches,ꢀtrace/connectorꢀresistancesꢀ operationꢀforꢀ3.3Vꢀandꢀ5Vꢀregulatorsꢀoverꢀaꢀwideꢀinputꢀ
andꢀprotectionꢀcircuitry.ꢀImprovementsꢀinꢀbothꢀconductedꢀ voltageꢀrange.
andꢀradiatedꢀEMIꢀalsoꢀdirectlyꢀaccrueꢀasꢀaꢀresultꢀofꢀtheꢀ
Itꢀcanꢀreadilyꢀbeꢀseenꢀthatꢀtheꢀadvantagesꢀofꢀ2-phaseꢀop-
reducedꢀRMSꢀinputꢀcurrentꢀandꢀvoltage.
erationꢀareꢀnotꢀjustꢀlimitedꢀtoꢀaꢀnarrowꢀoperatingꢀrange,ꢀ
Ofꢀcourse,ꢀtheꢀimprovementꢀaffordedꢀbyꢀ2-phaseꢀopera-
forꢀmostꢀapplicationsꢀisꢀthatꢀ2-phaseꢀoperationꢀwillꢀreduceꢀ
tionꢀisꢀaꢀfunctionꢀofꢀtheꢀdualꢀswitchingꢀregulator’sꢀrelativeꢀ theꢀinputꢀcapacitorꢀrequirementꢀtoꢀthatꢀforꢀjustꢀoneꢀchannelꢀ
dutyꢀcyclesꢀwhich,ꢀinꢀturn,ꢀareꢀdependentꢀuponꢀtheꢀinputꢀ operatingꢀatꢀmaximumꢀcurrentꢀandꢀ50%ꢀdutyꢀcycle.
3.0
SINGLE PHASE
DUAL CONTROLLER
2.5
2.0
1.5
1.0
0.5
0
2-PHASE
DUAL CONTROLLER
V
O1
V
O2
= 5V/3A
= 3.3V/3A
0
10
20
30
40
INPUT VOLTAGE (V)
3858 F03
Figure 3. RMS Input Current Comparison
3858fa
ꢀꢄ
LTC3858
applicaTions inForMaTion
Filterꢀcomponentsꢀmutualꢀtoꢀtheꢀsenseꢀlinesꢀshouldꢀbeꢀ
placedꢀcloseꢀtoꢀtheꢀLTC3858,ꢀandꢀtheꢀsenseꢀlinesꢀshouldꢀ
runꢀcloseꢀtogetherꢀtoꢀaꢀKelvinꢀconnectionꢀunderneathꢀtheꢀ
currentꢀsenseꢀelementꢀ(shownꢀinꢀFigureꢀ4).ꢀSensingꢀcur-
rentꢀelsewhereꢀcanꢀeffectivelyꢀaddꢀparasiticꢀinductanceꢀ
andꢀcapacitanceꢀtoꢀtheꢀcurrentꢀsenseꢀelement,ꢀdegradingꢀ
theꢀinformationꢀatꢀtheꢀsenseꢀterminalsꢀandꢀmakingꢀtheꢀ
programmedꢀcurrentꢀlimitꢀunpredictable.ꢀIfꢀinductorꢀDCRꢀ
sensingꢀisꢀusedꢀ(Figureꢀ5b),ꢀresistorꢀR1ꢀshouldꢀbeꢀplacedꢀ
closeꢀtoꢀtheꢀswitchingꢀnode,ꢀtoꢀpreventꢀnoiseꢀfromꢀcouplingꢀ
intoꢀsensitiveꢀsmall-signalꢀnodes.
TheꢀTypicalꢀApplicationꢀonꢀtheꢀfirstꢀpageꢀisꢀaꢀbasicꢀLTC3858ꢀ
applicationꢀ circuit.ꢀ LTC3858ꢀ canꢀ beꢀ configuredꢀ toꢀ useꢀ
eitherꢀ DCRꢀ (inductorꢀ resistance)ꢀ sensingꢀ orꢀ lowꢀ valueꢀ
resistorꢀ sensing.ꢀ Theꢀ choiceꢀ betweenꢀ theꢀ twoꢀ currentꢀ
sensingꢀ schemesꢀ isꢀ largelyꢀ aꢀ designꢀ tradeoffꢀ betweenꢀ
cost,ꢀ powerꢀ consumptionꢀ andꢀ accuracy.ꢀ DCRꢀ sensingꢀ
isꢀbecomingꢀpopularꢀbecauseꢀitꢀsavesꢀexpensiveꢀcurrentꢀ
sensingꢀresistorsꢀandꢀisꢀmoreꢀpowerꢀefficient,ꢀespeciallyꢀ
inꢀ highꢀ currentꢀ applications.ꢀ However,ꢀ currentꢀ sensingꢀ
resistorsꢀprovideꢀtheꢀmostꢀaccurateꢀcurrentꢀlimitsꢀforꢀtheꢀ
controller.ꢀOtherꢀexternalꢀcomponentꢀselectionꢀisꢀdrivenꢀ
byꢀtheꢀloadꢀrequirement,ꢀandꢀbeginsꢀwithꢀtheꢀselectionꢀofꢀ
TO SENSE FILTER,
NEXT TO THE CONTROLLER
R ꢀ(ifꢀR
SENSE
ꢀisꢀused)ꢀandꢀinductorꢀvalue.ꢀNext,ꢀtheꢀ
SENSE
powerꢀMOSFETsꢀandꢀSchottkyꢀdiodesꢀareꢀselected.ꢀFinally,ꢀ
inputꢀandꢀoutputꢀcapacitorsꢀareꢀselected.
C
OUT
3858 F04
INDUCTOR OR R
SENSE
Current Limit Programming
Figure 4. Sense Lines Placement with Inductor or Sense Resistor
TheꢀI ꢀpinꢀisꢀaꢀtri-levelꢀlogicꢀinputꢀwhichꢀsetsꢀtheꢀmaximumꢀ
LIM
currentꢀlimitꢀofꢀtheꢀconverter.ꢀWhenꢀI ꢀisꢀgrounded,ꢀtheꢀ
LIM
Low Value Resistor Current Sensing
maximumꢀcurrentꢀlimitꢀthresholdꢀvoltageꢀofꢀtheꢀcurrentꢀ
comparatorꢀisꢀprogrammedꢀtoꢀbeꢀ30mV.ꢀWhenꢀI ꢀisꢀ
LIM
Aꢀtypicalꢀsensingꢀcircuitꢀusingꢀaꢀdiscreteꢀresistorꢀisꢀshownꢀ
floated,ꢀtheꢀmaximumꢀcurrentꢀlimitꢀthresholdꢀisꢀ50mV.ꢀ
inꢀ Figureꢀ 5a.ꢀ R
outputꢀcurrent.
ꢀ isꢀ chosenꢀ basedꢀ onꢀ theꢀ requiredꢀ
SENSE
WhenꢀI ꢀisꢀtiedꢀtoꢀINTV ,ꢀtheꢀmaximumꢀcurrentꢀlimitꢀ
LIM
CC
thresholdꢀisꢀsetꢀtoꢀ75mV.
Theꢀ currentꢀ comparatorꢀ hasꢀ aꢀ maximumꢀ thresholdꢀ
ꢀdeterminedꢀbyꢀtheꢀI ꢀsetting.ꢀTheꢀcurrentꢀ
+
–
V
SENSE and SENSE Pins
SENSE(MAX)
LIM
comparatorꢀthresholdꢀvoltageꢀsetsꢀtheꢀpeakꢀofꢀtheꢀinduc-
torꢀcurrent,ꢀyieldingꢀaꢀmaximumꢀaverageꢀoutputꢀcurrent,ꢀ
+
–
TheꢀSENSE ꢀandꢀSENSE ꢀpinsꢀareꢀtheꢀinputsꢀtoꢀtheꢀcur-
rentꢀcomparators.ꢀTheꢀcommonꢀmodeꢀvoltageꢀrangeꢀonꢀ
theseꢀpinsꢀisꢀ0Vꢀtoꢀ28Vꢀ(AbsꢀMax),ꢀenablingꢀtheꢀLTC3858ꢀ
toꢀregulateꢀoutputꢀvoltagesꢀupꢀtoꢀaꢀnominalꢀ24Vꢀ(allowingꢀ
marginꢀforꢀtolerancesꢀandꢀtransients).ꢀ
I
,ꢀequalꢀtoꢀtheꢀpeakꢀvalueꢀlessꢀhalfꢀtheꢀpeak-to-peakꢀ
MAX
rippleꢀcurrent,ꢀ∆I .ꢀToꢀcalculateꢀtheꢀsenseꢀresistorꢀvalue,ꢀ
L
useꢀtheꢀequation:
VSENSE(MAX)
+
TheꢀSENSE ꢀpinꢀisꢀhighꢀimpedanceꢀoverꢀtheꢀfullꢀcommonꢀ
RSENSE
=
∆IL
modeꢀrange,ꢀdrawingꢀatꢀmostꢀ 1µA.ꢀThisꢀhighꢀimpedanceꢀ
allowsꢀtheꢀcurrentꢀcomparatorsꢀtoꢀbeꢀusedꢀinꢀinductorꢀ
DCRꢀsensing.
IMAX
+
ꢀ
2
Whenꢀusingꢀtheꢀcontrollerꢀinꢀveryꢀlowꢀdropoutꢀconditions,ꢀ
theꢀmaximumꢀoutputꢀcurrentꢀlevelꢀwillꢀbeꢀreducedꢀdueꢀtoꢀtheꢀ
internalꢀcompensationꢀrequiredꢀtoꢀmeetꢀstabilityꢀcriterionꢀ
forꢀbuckꢀregulatorsꢀoperatingꢀatꢀgreaterꢀthanꢀ50%ꢀdutyꢀ
factor.ꢀAꢀcurveꢀisꢀprovidedꢀinꢀtheꢀTypicalꢀPerformanceꢀChar-
acteristicsꢀsectionꢀtoꢀestimateꢀthisꢀreductionꢀinꢀpeakꢀoutputꢀ
currentꢀdependingꢀuponꢀtheꢀoperatingꢀdutyꢀfactor.
–
TheꢀimpedanceꢀofꢀtheꢀSENSE ꢀpinꢀchangesꢀdependingꢀonꢀ
–
theꢀcommonꢀmodeꢀvoltage.ꢀWhenꢀSENSE ꢀisꢀlessꢀthanꢀ
INTV ꢀ–ꢀ0.5V,ꢀaꢀsmallꢀcurrentꢀofꢀlessꢀthanꢀ1µAꢀflowsꢀoutꢀ
CC
–
ofꢀtheꢀpin.ꢀWhenꢀSENSE ꢀisꢀaboveꢀINTV ꢀ+ꢀ0.5V,ꢀaꢀhigherꢀ
CC
currentꢀ(~550µA)ꢀflowsꢀintoꢀtheꢀpin.ꢀBetweenꢀINTV ꢀ–ꢀ0.5Vꢀ
CC
andꢀINTV ꢀ+ꢀ0.5V,ꢀtheꢀcurrentꢀtransitionsꢀfromꢀtheꢀsmallerꢀ
CC
currentꢀtoꢀtheꢀhigherꢀcurrent.
3858fa
ꢀꢅ
LTC3858
applicaTions inForMaTion
Inductor DCR Sensing
Toꢀensureꢀthatꢀtheꢀapplicationꢀwillꢀdeliverꢀfullꢀloadꢀcurrentꢀ
overꢀ theꢀ fullꢀ operatingꢀ temperatureꢀ range,ꢀ chooseꢀ theꢀ
minimumꢀvalueꢀforꢀtheꢀMaximumꢀCurrentꢀSenseꢀThresh-
Forꢀapplicationsꢀrequiringꢀtheꢀhighestꢀpossibleꢀefficiencyꢀ
atꢀhighꢀloadꢀcurrents,ꢀtheꢀLTC3850ꢀisꢀcapableꢀofꢀsensingꢀ
theꢀvoltageꢀdropꢀacrossꢀtheꢀinductorꢀDCR,ꢀasꢀshownꢀinꢀ
Figureꢀ5b.ꢀTheꢀDCRꢀofꢀtheꢀinductorꢀrepresentsꢀtheꢀsmallꢀ
amountꢀofꢀDCꢀresistanceꢀofꢀtheꢀcopperꢀwire,ꢀwhichꢀcanꢀbeꢀ
lessꢀthanꢀ1mΩꢀforꢀtoday’sꢀlowꢀvalue,ꢀhighꢀcurrentꢀinductors.ꢀ
Inꢀaꢀhighꢀcurrentꢀapplicationꢀrequiringꢀsuchꢀanꢀinductor,ꢀ
powerꢀlossꢀthroughꢀaꢀsenseꢀresistorꢀwouldꢀcostꢀseveralꢀ
pointsꢀofꢀefficiencyꢀcomparedꢀtoꢀinductorꢀDCRꢀsensing.
oldꢀVoltageꢀ(V
)ꢀinꢀtheꢀElectricalꢀCharacteristicsꢀ
SENSE(MAX)
tableꢀ(30mV,ꢀ50mVꢀorꢀ75mVꢀdependingꢀonꢀtheꢀstateꢀofꢀ
theꢀI ꢀpin).
LIM
Next,ꢀdetermineꢀtheꢀDCRꢀofꢀtheꢀinductor.ꢀWhenꢀprovided,ꢀ
useꢀtheꢀmanufacturer’sꢀmaximumꢀvalue,ꢀusuallyꢀgivenꢀatꢀ
20°C.ꢀIncreaseꢀthisꢀvalueꢀtoꢀaccountꢀforꢀtheꢀtemperatureꢀ
coefficientꢀofꢀcopper,ꢀwhichꢀisꢀapproximatelyꢀ0.4%/°C.ꢀAꢀ
conservativeꢀvalueꢀforꢀT
ꢀisꢀ100°C.
L(MAX)
IfꢀtheꢀexternalꢀR1||R2ꢀ•ꢀC1ꢀtimeꢀconstantꢀisꢀchosenꢀtoꢀbeꢀ
exactlyꢀequalꢀtoꢀtheꢀL/DCRꢀtimeꢀconstant,ꢀtheꢀvoltageꢀdropꢀ
acrossꢀtheꢀexternalꢀcapacitorꢀisꢀequalꢀtoꢀtheꢀdropꢀacrossꢀ
theꢀinductorꢀDCRꢀmultipliedꢀbyꢀR2/(R1ꢀ+ꢀR2).ꢀR2ꢀscalesꢀtheꢀ
voltageꢀacrossꢀtheꢀsenseꢀterminalsꢀforꢀapplicationsꢀwhereꢀ
theꢀDCRꢀisꢀgreaterꢀthanꢀtheꢀtargetꢀsenseꢀresistorꢀvalue.ꢀ
Toꢀproperlyꢀdimensionꢀtheꢀexternalꢀfilterꢀcomponents,ꢀtheꢀ
DCRꢀofꢀtheꢀinductorꢀmustꢀbeꢀknown.ꢀItꢀcanꢀbeꢀmeasuredꢀ
usingꢀaꢀgoodꢀRLCꢀmeter,ꢀbutꢀtheꢀDCRꢀtoleranceꢀisꢀnotꢀ
alwaysꢀtheꢀsameꢀandꢀvariesꢀwithꢀtemperature;ꢀconsultꢀtheꢀ
manufacturers’ꢀdataꢀsheetsꢀforꢀdetailedꢀinformation.
ToꢀscaleꢀtheꢀmaximumꢀinductorꢀDCRꢀtoꢀtheꢀdesiredꢀsenseꢀ
resistorꢀ(R )ꢀvalue,ꢀuseꢀtheꢀdividerꢀratio:
D
RSENSE(EQUIV)
RD =
DCRMAX atT
L(MAX)
ꢀ
C1ꢀisꢀusuallyꢀselectedꢀtoꢀbeꢀinꢀtheꢀrangeꢀofꢀ0.1µFꢀtoꢀ0.47µF.ꢀ
ThisꢀforcesꢀR1||R2ꢀtoꢀaroundꢀ2k,ꢀreducingꢀerrorꢀthatꢀmightꢀ
+
haveꢀbeenꢀcausedꢀbyꢀtheꢀSENSE ꢀpin’sꢀ 1µAꢀcurrent.
TheꢀequivalentꢀresistanceꢀR1||R2ꢀisꢀscaledꢀtoꢀtheꢀroomꢀ
temperatureꢀinductanceꢀandꢀmaximumꢀDCR:
UsingꢀtheꢀinductorꢀrippleꢀcurrentꢀvalueꢀfromꢀtheꢀInductorꢀ
ValueꢀCalculationꢀsection,ꢀtheꢀtargetꢀsenseꢀresistorꢀvalueꢀ
is:
L
R1||R2 =
DCR at 20°C •C1
ꢀ
VSENSE(MAX)
RSENSE(EQUIV)
=
∆IL
IMAX
+
ꢀ
2
V
V
IN
V
IN
V
IN
IN
INTV
INTV
CC
CC
INDUCTOR
DCR
BOOST
TG
BOOST
TG
R
SENSE
L
SW
V
OUT
SW
V
OUT
LTC3858
LTC3858
BG
BG
R1
C1* R2
+
+
SENSE
SENSE
PLACE CAPACITOR NEAR
SENSE PINS
–
–
SENSE
SGND
SENSE
SGND
3858 F05b
R2
R1 + R2
3858 F05a
L
DCR
||
(R1 R2) • C1 =
*PLACE C1 NEAR
SENSE PINS
R
= DCR
SENSE(EQ)
(5a) Using a Resistor to Sense Current
(5b) Using the Inductor DCR to Sense Current
Figure 5. Current Sensing Methods
3858fa
ꢀꢆ
LTC3858
applicaTions inForMaTion
Theꢀsenseꢀresistorꢀꢀvaluesꢀare:
settingꢀrippleꢀcurrentꢀisꢀ∆I ꢀ=ꢀ0.3(I
).ꢀTheꢀmaximumꢀ
MAX
L
∆I ꢀoccursꢀatꢀtheꢀmaximumꢀinputꢀvoltage.
L
R1•RD
1–RD
R1||R2
RD
R1=
; R2 =
Theꢀinductorꢀvalueꢀalsoꢀhasꢀsecondaryꢀeffects.ꢀTheꢀtran-
sitionꢀtoꢀBurstꢀModeꢀoperationꢀbeginsꢀwhenꢀtheꢀaverageꢀ
inductorꢀcurrentꢀrequiredꢀresultsꢀinꢀaꢀpeakꢀcurrentꢀbelowꢀ
ꢀ
TheꢀmaximumꢀpowerꢀlossꢀinꢀR1ꢀisꢀrelatedꢀtoꢀdutyꢀcycle,ꢀ
andꢀwillꢀoccurꢀinꢀcontinuousꢀmodeꢀatꢀtheꢀmaximumꢀinputꢀ
voltage:
30%ꢀofꢀtheꢀcurrentꢀlimitꢀdeterminedꢀbyꢀR
.ꢀLowerꢀ
SENSE
inductorꢀvaluesꢀ(higherꢀ∆I )ꢀwillꢀcauseꢀthisꢀtoꢀoccurꢀatꢀ
L
lowerꢀloadꢀcurrents,ꢀwhichꢀcanꢀcauseꢀaꢀdipꢀinꢀefficiencyꢀinꢀ
theꢀupperꢀrangeꢀofꢀlowꢀcurrentꢀoperation.ꢀInꢀBurstꢀModeꢀ
operation,ꢀlowerꢀinductanceꢀvaluesꢀwillꢀcauseꢀtheꢀburstꢀ
frequencyꢀtoꢀdecrease.
V
IN(MAX) – VOUT • V
(
)
OUT
P
R1=
LOSS
R1
ꢀ
EnsureꢀthatꢀR1ꢀhasꢀaꢀpowerꢀratingꢀhigherꢀthanꢀthisꢀvalue.ꢀ
Ifꢀ highꢀ efficiencyꢀ isꢀ necessaryꢀ atꢀ lightꢀ loads,ꢀ considerꢀ
thisꢀpowerꢀlossꢀwhenꢀdecidingꢀwhetherꢀtoꢀuseꢀinductorꢀ
DCRꢀsensingꢀorꢀsenseꢀresistors.ꢀLightꢀloadꢀpowerꢀlossꢀ
canꢀbeꢀmodestlyꢀhigherꢀwithꢀaꢀDCRꢀnetworkꢀthanꢀwithꢀaꢀ
senseꢀresistor,ꢀdueꢀtoꢀtheꢀextraꢀswitchingꢀlossesꢀincurredꢀ
throughꢀR1.ꢀHowever,ꢀDCRꢀsensingꢀeliminatesꢀaꢀsenseꢀ
resistor,ꢀreducesꢀconductionꢀlossesꢀandꢀprovidesꢀhigherꢀ
efficiencyꢀatꢀheavyꢀloads.ꢀPeakꢀefficiencyꢀisꢀaboutꢀtheꢀsameꢀ
withꢀeitherꢀmethod.
Inductor Core Selection
OnceꢀtheꢀvalueꢀforꢀLꢀisꢀknown,ꢀtheꢀtypeꢀofꢀinductorꢀmustꢀ
beꢀselected.ꢀHighꢀefficiencyꢀconvertersꢀgenerallyꢀcannotꢀ
affordꢀtheꢀcoreꢀlossꢀfoundꢀinꢀlowꢀcostꢀpowderedꢀironꢀcores,ꢀ
forcingꢀtheꢀuseꢀofꢀmoreꢀexpensiveꢀferriteꢀorꢀmolypermalloyꢀ
cores.ꢀActualꢀcoreꢀlossꢀisꢀindependentꢀofꢀcoreꢀsizeꢀforꢀaꢀ
fixedꢀinductorꢀvalue,ꢀbutꢀitꢀisꢀveryꢀdependentꢀonꢀinductanceꢀ
valueꢀselected.ꢀAsꢀinductanceꢀincreases,ꢀcoreꢀlossesꢀgoꢀ
down.ꢀUnfortunately,ꢀincreasedꢀinductanceꢀrequiresꢀmoreꢀ
turnsꢀofꢀwireꢀandꢀthereforeꢀcopperꢀlossesꢀwillꢀincrease.
Inductor Value Calculation
Ferriteꢀdesignsꢀhaveꢀveryꢀlowꢀcoreꢀlossꢀandꢀareꢀpreferredꢀ
forꢀhighꢀswitchingꢀfrequencies,ꢀsoꢀdesignꢀgoalsꢀcanꢀcon-
centrateꢀonꢀcopperꢀlossꢀandꢀpreventingꢀsaturation.ꢀFerriteꢀ
coreꢀmaterialꢀsaturatesꢀ“hard,”ꢀwhichꢀmeansꢀthatꢀinduc-
tanceꢀcollapsesꢀabruptlyꢀwhenꢀtheꢀpeakꢀdesignꢀcurrentꢀisꢀ
exceeded.ꢀThisꢀresultsꢀinꢀanꢀabruptꢀincreaseꢀinꢀinductorꢀ
rippleꢀcurrentꢀandꢀconsequentꢀoutputꢀvoltageꢀripple.ꢀDoꢀ
notꢀallowꢀtheꢀcoreꢀtoꢀsaturate!
Theꢀoperatingꢀfrequencyꢀandꢀinductorꢀselectionꢀareꢀinter-
relatedꢀinꢀthatꢀhigherꢀoperatingꢀfrequenciesꢀallowꢀtheꢀuseꢀ
ofꢀsmallerꢀinductorꢀandꢀcapacitorꢀvalues.ꢀSoꢀwhyꢀwouldꢀ
anyoneꢀeverꢀchooseꢀtoꢀoperateꢀatꢀlowerꢀfrequenciesꢀwithꢀ
largerꢀcomponents?ꢀTheꢀanswerꢀisꢀefficiency.ꢀAꢀhigherꢀ
frequencyꢀgenerallyꢀresultsꢀinꢀlowerꢀefficiencyꢀbecauseꢀ
ofꢀMOSFETꢀgateꢀchargeꢀlosses.ꢀInꢀadditionꢀtoꢀthisꢀbasicꢀ
tradeoff,ꢀtheꢀeffectꢀofꢀinductorꢀvalueꢀonꢀrippleꢀcurrentꢀandꢀ
lowꢀcurrentꢀoperationꢀmustꢀalsoꢀbeꢀconsidered.
Power MOSFET and Schottky Diode (Optional)
Selection
Theꢀinductorꢀvalueꢀhasꢀaꢀdirectꢀeffectꢀonꢀrippleꢀcurrent.ꢀTheꢀ
inductorꢀrippleꢀcurrentꢀ∆I ꢀdecreasesꢀwithꢀhigherꢀinduc-
L
TwoꢀexternalꢀpowerꢀMOSFETsꢀmustꢀbeꢀselectedꢀforꢀeachꢀ
controllerꢀinꢀtheꢀLTC3858:ꢀoneꢀN-channelꢀMOSFETꢀforꢀtheꢀ
topꢀ(main)ꢀswitch,ꢀandꢀoneꢀN-channelꢀMOSFETꢀforꢀtheꢀ
bottomꢀ(synchronous)ꢀswitch.
tanceꢀorꢀhigherꢀfrequencyꢀandꢀincreasesꢀwithꢀhigherꢀV :
IN
VOUT
1
∆IL =
VOUT 1–
V
f L
IN
ꢀ
Theꢀpeak-to-peakꢀdriveꢀlevelsꢀareꢀsetꢀbyꢀtheꢀINTV ꢀvoltage.ꢀ
CC
Acceptingꢀ largerꢀ valuesꢀ ofꢀ ∆I ꢀ allowsꢀ theꢀ useꢀ ofꢀ lowꢀ
L
Thisꢀvoltageꢀisꢀtypicallyꢀ5.2Vꢀduringꢀstart-upꢀ(seeꢀEXTV ꢀ
CC
inductances,ꢀbutꢀresultsꢀinꢀhigherꢀoutputꢀvoltageꢀrippleꢀ
Pinꢀ Connection).ꢀ Consequently,ꢀ logic-levelꢀ thresholdꢀ
andꢀgreaterꢀcoreꢀlosses.ꢀAꢀreasonableꢀstartingꢀpointꢀforꢀ
MOSFETsꢀmustꢀbeꢀusedꢀinꢀmostꢀapplications.ꢀTheꢀonlyꢀ
3858fa
ꢀꢇ
LTC3858
applicaTions inForMaTion
2
BothꢀMOSFETsꢀhaveꢀI RꢀlossesꢀwhileꢀtheꢀtopsideꢀN-channelꢀ
equationꢀincludesꢀanꢀadditionalꢀtermꢀforꢀtransitionꢀlosses,ꢀ
exceptionꢀisꢀifꢀlowꢀinputꢀvoltageꢀisꢀexpectedꢀ(V ꢀ<ꢀ4V);ꢀ
IN
GS(TH)
then,ꢀsub-logicꢀlevelꢀthresholdꢀMOSFETsꢀ(V
ꢀ<ꢀ3V)ꢀ
whichꢀareꢀhighestꢀatꢀhighꢀinputꢀvoltages.ꢀForꢀV ꢀ<ꢀ20Vꢀ
shouldꢀbeꢀused.ꢀPayꢀcloseꢀattentionꢀtoꢀtheꢀBV ꢀspeci-
IN
DSS
theꢀhighꢀcurrentꢀefficiencyꢀgenerallyꢀimprovesꢀwithꢀlargerꢀ
ficationꢀforꢀtheꢀMOSFETsꢀasꢀwell;ꢀmanyꢀofꢀtheꢀlogic-levelꢀ
MOSFETs,ꢀwhileꢀforꢀV ꢀ>ꢀ20Vꢀtheꢀtransitionꢀlossesꢀrapidlyꢀ
MOSFETsꢀareꢀlimitedꢀtoꢀ30Vꢀorꢀless.
IN
increaseꢀtoꢀtheꢀpointꢀthatꢀtheꢀuseꢀofꢀaꢀhigherꢀR
ꢀdeviceꢀ
DS(ON)
SelectionꢀcriteriaꢀforꢀtheꢀpowerꢀMOSFETsꢀincludeꢀtheꢀ“ON”ꢀ
withꢀlowerꢀC
ꢀactuallyꢀprovidesꢀhigherꢀefficiency.ꢀTheꢀ
MILLER
resistance,ꢀ R
,ꢀ Millerꢀ capacitance,ꢀ C ,ꢀ inputꢀ
DS(ON) MILLER
synchronousꢀMOSFETꢀlossesꢀareꢀgreatestꢀatꢀhighꢀinputꢀ
voltageꢀwhenꢀtheꢀtopꢀswitchꢀdutyꢀfactorꢀisꢀlowꢀorꢀduringꢀ
aꢀshort-circuitꢀwhenꢀtheꢀsynchronousꢀswitchꢀisꢀonꢀcloseꢀ
toꢀ100%ꢀofꢀtheꢀperiod.
voltageꢀandꢀmaximumꢀoutputꢀcurrent.ꢀMillerꢀcapacitance,ꢀ
,ꢀcanꢀbeꢀapproximatedꢀfromꢀtheꢀgateꢀchargeꢀcurveꢀ
C
MILLER
usuallyꢀ providedꢀ onꢀ theꢀ MOSFETꢀ manufacturers’ꢀ dataꢀ
sheet.ꢀC
ꢀisꢀequalꢀtoꢀtheꢀincreaseꢀinꢀgateꢀchargeꢀ
MILLER
Theꢀtermꢀ(1+ꢀδ)ꢀisꢀgenerallyꢀgivenꢀforꢀaꢀMOSFETꢀinꢀtheꢀ
alongꢀtheꢀhorizontalꢀaxisꢀwhileꢀtheꢀcurveꢀisꢀapproximatelyꢀ
formꢀofꢀaꢀnormalizedꢀR
ꢀvsꢀTemperatureꢀcurve,ꢀbutꢀ
DS(ON)
flatꢀdividedꢀbyꢀtheꢀspecifiedꢀchangeꢀinꢀV .ꢀThisꢀresultꢀisꢀ
DS
δꢀ=ꢀ0.005/°Cꢀcanꢀbeꢀusedꢀasꢀanꢀapproximationꢀforꢀlowꢀ
thenꢀmultipliedꢀbyꢀtheꢀratioꢀofꢀtheꢀapplicationꢀappliedꢀV ꢀ
DS
voltageꢀMOSFETs.
toꢀtheꢀgateꢀchargeꢀcurveꢀspecifiedꢀV .ꢀWhenꢀtheꢀICꢀisꢀ
DS
operatingꢀinꢀcontinuousꢀmodeꢀtheꢀdutyꢀcyclesꢀforꢀtheꢀtopꢀ
TheꢀoptionalꢀSchottkyꢀdiodesꢀD3ꢀandꢀD4ꢀshownꢀinꢀFigureꢀ12ꢀ
conductꢀduringꢀtheꢀdead-timeꢀbetweenꢀtheꢀconductionꢀofꢀ
theꢀtwoꢀpowerꢀMOSFETs.ꢀThisꢀpreventsꢀtheꢀbodyꢀdiodeꢀofꢀ
theꢀbottomꢀMOSFETꢀfromꢀturningꢀon,ꢀstoringꢀchargeꢀduringꢀ
theꢀdead-timeꢀandꢀrequiringꢀaꢀreverseꢀrecoveryꢀperiodꢀthatꢀ
andꢀbottomꢀMOSFETsꢀareꢀgivenꢀby:
VOUT
Main Switch Duty Cycle =
V
IN
V − VOUT
IN
couldꢀcostꢀasꢀmuchꢀasꢀ3%ꢀinꢀefficiencyꢀatꢀhighꢀV .ꢀAꢀ1Aꢀ
IN
Synchronous Switch Duty Cycle =
V
toꢀ3AꢀSchottkyꢀisꢀgenerallyꢀaꢀgoodꢀcompromiseꢀforꢀbothꢀ
regionsꢀofꢀoperationꢀdueꢀtoꢀtheꢀrelativelyꢀsmallꢀaverageꢀ
current.ꢀLargerꢀdiodesꢀresultꢀinꢀadditionalꢀtransitionꢀlossesꢀ
dueꢀtoꢀtheirꢀlargerꢀjunctionꢀcapacitance.
IN
ꢀ
Theꢀ MOSFETꢀ powerꢀ dissipationsꢀ atꢀ maximumꢀ outputꢀ
currentꢀareꢀgivenꢀby:
VOUT
2
C and C
Selection
PMAIN
=
I
1+ δ R
+
(
MAX) (
)
IN
OUT
DS(ON)
V
IN
TheꢀselectionꢀofꢀC ꢀisꢀsimplifiedꢀbyꢀtheꢀ2-phaseꢀarchitec-
IN
IMAX
2
2
tureꢀandꢀitsꢀimpactꢀonꢀtheꢀworst-caseꢀRMSꢀcurrentꢀdrawnꢀ
throughꢀtheꢀinputꢀnetworkꢀ(battery/fuse/capacitor).ꢀItꢀcanꢀbeꢀ
shownꢀthatꢀtheꢀworst-caseꢀcapacitorꢀRMSꢀcurrentꢀoccursꢀ
whenꢀonlyꢀoneꢀcontrollerꢀisꢀoperating.ꢀTheꢀcontrollerꢀwithꢀ
V
R
C
•
(
)
(
DR )(
)
IN
MILLER
1
1
+
f
( )
VINTVCC – VTHMIN VTHMIN
theꢀhighestꢀ(V )(I )ꢀproductꢀneedsꢀtoꢀbeꢀusedꢀinꢀtheꢀ
OUT OUT
formulaꢀshownꢀinꢀEquationꢀ1ꢀtoꢀdetermineꢀtheꢀmaximumꢀ
RMSꢀcapacitorꢀcurrentꢀrequirement.ꢀIncreasingꢀtheꢀout-
putꢀcurrentꢀdrawnꢀfromꢀtheꢀotherꢀcontrollerꢀwillꢀactuallyꢀ
decreaseꢀtheꢀinputꢀRMSꢀrippleꢀcurrentꢀfromꢀitsꢀmaximumꢀ
value.ꢀTheꢀout-of-phaseꢀtechniqueꢀtypicallyꢀreducesꢀtheꢀ
inputꢀcapacitor’sꢀRMSꢀrippleꢀcurrentꢀbyꢀaꢀfactorꢀofꢀ30%ꢀ
toꢀ70%ꢀwhenꢀcomparedꢀtoꢀaꢀsingleꢀphaseꢀpowerꢀsupplyꢀ
solution.
V – VOUT
2
IN
PSYNC
=
I
1+ δ R
(
MAX) (
)
DS(ON)
V
IN
ꢀ
whereꢀδꢀisꢀtheꢀtemperatureꢀdependencyꢀofꢀR
R ꢀ(approximatelyꢀ2Ω)ꢀisꢀtheꢀeffectiveꢀdriverꢀresistanceꢀ
atꢀtheꢀMOSFET’sꢀMillerꢀthresholdꢀvoltage.ꢀV
typicalꢀMOSFETꢀminimumꢀthresholdꢀvoltage.
ꢀandꢀ
DS(ON)
DR
ꢀisꢀtheꢀ
THMIN
3858fa
ꢀꢈ
LTC3858
applicaTions inForMaTion
Inꢀcontinuousꢀmode,ꢀtheꢀsourceꢀcurrentꢀofꢀtheꢀtopꢀMOSFETꢀ
isꢀaꢀsquareꢀwaveꢀofꢀdutyꢀcycleꢀ(V )/(V ).ꢀToꢀpreventꢀ
theꢀV ꢀpinꢀprovidesꢀfurtherꢀisolationꢀbetweenꢀtheꢀtwoꢀ
IN
channels.
OUT
IN
largeꢀvoltageꢀtransients,ꢀaꢀlowꢀESRꢀcapacitorꢀsizedꢀforꢀtheꢀ
maximumꢀRMSꢀcurrentꢀofꢀoneꢀchannelꢀmustꢀbeꢀused.ꢀTheꢀ
maximumꢀRMSꢀcapacitorꢀcurrentꢀisꢀgivenꢀby:
TheꢀselectionꢀofꢀC ꢀisꢀdrivenꢀbyꢀtheꢀeffectiveꢀseriesꢀ
OUT
resistanceꢀ(ESR).ꢀTypically,ꢀonceꢀtheꢀESRꢀrequirementꢀ
isꢀsatisfied,ꢀtheꢀcapacitanceꢀisꢀadequateꢀforꢀfiltering.ꢀTheꢀ
outputꢀrippleꢀ(∆V )ꢀisꢀapproximatedꢀby:
1/2
IMAX
OUT
CIN Required IRMS
≈
V
OUT )(
V – V
(1)
ꢀ
(
)
IN
OUT
V
IN
1
∆VOUT ≈ ∆IL ESR +
8 • f •C
OUT
ꢀ
Equationꢀ1ꢀhasꢀaꢀmaximumꢀatꢀV ꢀ=ꢀ2V ,ꢀwhereꢀI
ꢀ
IN
OUTꢀ
RMS
=ꢀI /2.ꢀThisꢀsimpleꢀworst-caseꢀconditionꢀisꢀcommonlyꢀ
OUT
whereꢀf ꢀisꢀtheꢀoperatingꢀfrequency,ꢀC ꢀisꢀtheꢀoutputꢀ
O
OUT
usedꢀforꢀdesignꢀbecauseꢀevenꢀsignificantꢀdeviationsꢀdoꢀnotꢀ
offerꢀmuchꢀrelief.ꢀNoteꢀthatꢀcapacitorꢀmanufacturers’ꢀrippleꢀ
currentꢀratingsꢀareꢀoftenꢀbasedꢀonꢀonlyꢀ2000ꢀhoursꢀofꢀlife.ꢀ
Thisꢀmakesꢀitꢀadvisableꢀtoꢀfurtherꢀderateꢀtheꢀcapacitor,ꢀorꢀ
toꢀchooseꢀaꢀcapacitorꢀratedꢀatꢀaꢀhigherꢀtemperatureꢀthanꢀ
required.ꢀSeveralꢀcapacitorsꢀmayꢀbeꢀparalleledꢀtoꢀmeetꢀ
sizeꢀorꢀheightꢀrequirementsꢀinꢀtheꢀdesign.ꢀDueꢀtoꢀtheꢀhighꢀ
operatingꢀfrequencyꢀofꢀtheꢀLTC3858,ꢀceramicꢀcapacitorsꢀ
capacitanceꢀandꢀ∆I ꢀisꢀtheꢀrippleꢀcurrentꢀinꢀtheꢀinductor.ꢀ
L
Theꢀoutputꢀrippleꢀisꢀhighestꢀatꢀmaximumꢀinputꢀvoltageꢀ
sinceꢀ∆I ꢀincreasesꢀwithꢀinputꢀvoltage.
L
Setting Output Voltage
TheꢀLTC3858ꢀoutputꢀvoltagesꢀareꢀeachꢀsetꢀbyꢀanꢀexternalꢀ
feedbackꢀresistorꢀdividerꢀcarefullyꢀplacedꢀacrossꢀtheꢀout-
put,ꢀasꢀshownꢀinꢀFigureꢀ6.ꢀTheꢀregulatedꢀoutputꢀvoltageꢀ
isꢀdeterminedꢀby:
canꢀalsoꢀbeꢀusedꢀforꢀC .ꢀAlwaysꢀconsultꢀtheꢀmanufacturerꢀ
IN
ifꢀthereꢀisꢀanyꢀquestion.
RB
R
Theꢀbenefitꢀofꢀ2-phaseꢀoperationꢀcanꢀbeꢀcalculatedꢀbyꢀ
usingꢀ Equationꢀ 1ꢀ forꢀ theꢀ higherꢀ powerꢀ controllerꢀ andꢀ
thenꢀcalculatingꢀtheꢀlossꢀthatꢀwouldꢀhaveꢀresultedꢀifꢀbothꢀ
controllerꢀchannelsꢀswitchedꢀonꢀatꢀtheꢀsameꢀtime.ꢀTheꢀ
totalꢀRMSꢀpowerꢀlostꢀisꢀlowerꢀwhenꢀbothꢀcontrollersꢀareꢀ
operatingꢀdueꢀtoꢀtheꢀreducedꢀoverlapꢀofꢀcurrentꢀpulsesꢀ
requiredꢀthroughꢀtheꢀinputꢀcapacitor’sꢀESR.ꢀThisꢀisꢀwhyꢀ
theꢀinputꢀcapacitor’sꢀrequirementꢀcalculatedꢀaboveꢀforꢀtheꢀ
worst-caseꢀcontrollerꢀisꢀadequateꢀforꢀtheꢀdualꢀcontrollerꢀ
design.ꢀAlso,ꢀtheꢀinputꢀprotectionꢀfuseꢀresistance,ꢀbatteryꢀ
resistance,ꢀandꢀPCꢀboardꢀtraceꢀresistanceꢀlossesꢀareꢀalsoꢀ
reducedꢀdueꢀtoꢀtheꢀreducedꢀpeakꢀcurrentsꢀinꢀaꢀ2-phaseꢀ
system.ꢀTheꢀoverallꢀbenefitꢀofꢀaꢀmultiphaseꢀdesignꢀwillꢀ
onlyꢀbeꢀfullyꢀrealizedꢀwhenꢀtheꢀsourceꢀimpedanceꢀofꢀtheꢀ
powerꢀsupply/batteryꢀisꢀincludedꢀinꢀtheꢀefficiencyꢀtesting.ꢀ
TheꢀdrainsꢀofꢀtheꢀtopꢀMOSFETsꢀshouldꢀbeꢀplacedꢀwithinꢀ
VOUT = 0.8V 1+
A
ꢀ
Toꢀimproveꢀtheꢀfrequencyꢀresponse,ꢀaꢀfeedforwardꢀca-
pacitor,ꢀC ,ꢀmayꢀbeꢀused.ꢀGreatꢀcareꢀshouldꢀbeꢀtakenꢀtoꢀ
FFꢀ
FB
routeꢀtheꢀV ꢀlineꢀawayꢀfromꢀnoiseꢀsources,ꢀsuchꢀasꢀtheꢀ
inductorꢀorꢀtheꢀSWꢀline.
V
OUT
R
C
FF
1/2 LTC3858
B
A
V
FB
R
3858 F06
Figure 6. Setting Output Voltage
Soft-Start (SS Pins)
1cmꢀofꢀeachꢀotherꢀandꢀshareꢀaꢀcommonꢀC ꢀ(s).ꢀSeparat-
IN
Theꢀstart-upꢀofꢀeachꢀV ꢀisꢀcontrolledꢀbyꢀtheꢀvoltageꢀonꢀ
OUT
ingꢀtheꢀsourcesꢀandꢀC ꢀmayꢀproduceꢀundesirableꢀvoltageꢀ
IN
theꢀrespectiveꢀSSꢀpin.ꢀWhenꢀtheꢀvoltageꢀonꢀtheꢀSSꢀpinꢀisꢀ
andꢀcurrentꢀresonancesꢀatꢀV .
IN
lessꢀthanꢀtheꢀinternalꢀ0.8Vꢀreference,ꢀtheꢀLTC3858ꢀregulatesꢀ
Aꢀsmallꢀ(0.1µFꢀtoꢀ1µF)ꢀbypassꢀcapacitorꢀbetweenꢀtheꢀchipꢀ
theꢀV ꢀpinꢀvoltageꢀtoꢀtheꢀvoltageꢀonꢀtheꢀSSꢀpinꢀinsteadꢀ
FB
V ꢀpinꢀandꢀground,ꢀplacedꢀcloseꢀtoꢀtheꢀLTC3858,ꢀisꢀalsoꢀ
ofꢀ0.8V.ꢀTheꢀSSꢀpinꢀcanꢀbeꢀusedꢀtoꢀprogramꢀanꢀexternalꢀ
IN
suggested.ꢀAꢀ10ΩꢀresistorꢀplacedꢀbetweenꢀC ꢀ(C1)ꢀandꢀ
soft-startꢀfunction.
IN
3858fa
ꢁ0
LTC3858
applicaTions inForMaTion
Soft-startꢀisꢀenabledꢀbyꢀsimplyꢀconnectingꢀaꢀcapacitorꢀfromꢀ
theꢀSSꢀpinꢀtoꢀground,ꢀasꢀshownꢀinꢀFigureꢀ7.ꢀAnꢀinternalꢀ1µAꢀ
currentꢀsourceꢀchargesꢀtheꢀcapacitor,ꢀprovidingꢀaꢀlinearꢀ
rampingꢀvoltageꢀatꢀtheꢀSSꢀpin.ꢀTheꢀLTC3858ꢀwillꢀregulateꢀ
theꢀV ꢀpinꢀ(andꢀhenceꢀV )ꢀaccordingꢀtoꢀtheꢀvoltageꢀonꢀ
asꢀ discussedꢀ inꢀ theꢀ Efficiencyꢀ Considerationsꢀ section.ꢀ
Theꢀjunctionꢀtemperatureꢀcanꢀbeꢀestimatedꢀbyꢀusingꢀtheꢀ
equationsꢀgivenꢀinꢀNoteꢀ3ꢀofꢀtheꢀElectricalꢀCharacteristics.ꢀ
Forꢀexample,ꢀtheꢀLTC3858ꢀINTV ꢀcurrentꢀisꢀlimitedꢀtoꢀlessꢀ
CC
thanꢀ32mAꢀfromꢀaꢀ40VꢀsupplyꢀwhenꢀnotꢀusingꢀtheꢀEXTV ꢀ
FB
OUT
CC
theꢀSSꢀpin,ꢀallowingꢀV ꢀtoꢀriseꢀsmoothlyꢀfromꢀ0Vꢀtoꢀ
supplyꢀatꢀ70°Cꢀambientꢀtemperature:
OUT
itsꢀfinalꢀregulatedꢀvalue.ꢀTheꢀtotalꢀsoft-startꢀtimeꢀwillꢀbeꢀ
approximately:
ꢀ T ꢀ=ꢀ70°Cꢀ+ꢀ(32mA)(40V)(43°C/W)ꢀ=ꢀ125°C
J
Toꢀpreventꢀtheꢀmaximumꢀjunctionꢀtemperatureꢀfromꢀbe-
ingꢀexceeded,ꢀtheꢀinputꢀsupplyꢀcurrentꢀmustꢀbeꢀcheckedꢀ
whileꢀoperatingꢀinꢀforcedꢀcontinuousꢀmodeꢀ(PLLIN/MODEꢀ
0.8V
1µA
tSS = CSS
•
ꢀ
=ꢀINTV )ꢀatꢀmaximumꢀV .
CC
IN
1/2 LTC3858
SS
WhenꢀtheꢀvoltageꢀappliedꢀtoꢀEXTV ꢀrisesꢀaboveꢀ4.7V,ꢀtheꢀ
CC
V ꢀLDOꢀisꢀturnedꢀoffꢀandꢀtheꢀEXTV ꢀLDOꢀisꢀenabled.ꢀTheꢀ
C
IN
CC
SS
EXTV ꢀLDOꢀremainsꢀonꢀasꢀlongꢀasꢀtheꢀvoltageꢀappliedꢀtoꢀ
SGND
CC
EXTV ꢀremainsꢀaboveꢀ4.5V.ꢀTheꢀEXTV ꢀLDOꢀattemptsꢀ
3858 F07
CC
CC
toꢀregulateꢀtheꢀINTV ꢀvoltageꢀtoꢀ5.1V,ꢀsoꢀwhileꢀEXTV ꢀ
CC
CC
Figure 7. Using the TRACK/SS Pin to Program Soft-Start
isꢀlessꢀthanꢀ5.1V,ꢀtheꢀLDOꢀisꢀinꢀdropoutꢀandꢀtheꢀINTV ꢀ
CC
voltageꢀisꢀapproximatelyꢀequalꢀtoꢀEXTV .ꢀWhenꢀEXTV ꢀ
CC
CC
INTV Regulators
CC
isꢀgreaterꢀthanꢀ5.1V,ꢀupꢀtoꢀanꢀabsoluteꢀmaximumꢀofꢀ14V,ꢀ
INTV ꢀisꢀregulatedꢀtoꢀ5.1V.
CC
TheꢀLTC3858ꢀfeaturesꢀtwoꢀseparateꢀinternalꢀP-channelꢀlowꢀ
dropoutꢀlinearꢀregulatorsꢀ(LDO)ꢀthatꢀsupplyꢀpowerꢀatꢀtheꢀ
UsingꢀtheꢀEXTVCCꢀLDOꢀallowsꢀtheꢀMOSFETꢀdriverꢀandꢀ
controlꢀpowerꢀtoꢀbeꢀderivedꢀfromꢀoneꢀofꢀtheꢀswitchingꢀ
regulatorꢀoutputsꢀ(4.7Vꢀ≤ꢀVOUTꢀ≤ꢀ14V)ꢀduringꢀnormalꢀ
operationꢀandꢀfromꢀtheꢀVINꢀLDOꢀwhenꢀtheꢀoutputꢀisꢀoutꢀ
ofꢀregulationꢀ(e.g.,ꢀstart-up,ꢀshort-circuit).ꢀIfꢀmoreꢀcurrentꢀ
isꢀrequiredꢀthroughꢀtheꢀEXTVCCꢀLDOꢀthanꢀisꢀspecified,ꢀanꢀ
externalꢀSchottkyꢀdiodeꢀcanꢀbeꢀaddedꢀbetweenꢀtheꢀEXTVCCꢀ
andꢀINTVCCꢀpins.ꢀInꢀthisꢀcase,ꢀdoꢀnotꢀapplyꢀmoreꢀthanꢀ6Vꢀ
toꢀtheꢀEXTVCCꢀpinꢀandꢀmakeꢀsureꢀthatꢀEXTVCCꢀ≤ꢀVIN.
INTV ꢀpinꢀfromꢀeitherꢀtheꢀV ꢀsupplyꢀpinꢀorꢀtheꢀEXTV ꢀ
CC
IN
CC
CC
pinꢀdependingꢀonꢀtheꢀconnectionꢀofꢀtheꢀEXTV ꢀpin.ꢀINTV ꢀ
CC
powersꢀtheꢀgateꢀdriversꢀandꢀmuchꢀofꢀtheꢀinternalꢀcircuitry.ꢀ
TheꢀV ꢀLDOꢀandꢀtheꢀEXTV ꢀLDOꢀregulateꢀINTV ꢀtoꢀ5.1V.ꢀ
IN
CC
CC
Eachꢀofꢀtheseꢀcanꢀsupplyꢀaꢀpeakꢀcurrentꢀofꢀ50mAꢀandꢀmustꢀ
beꢀbypassedꢀtoꢀgroundꢀwithꢀaꢀminimumꢀofꢀ4.7µFꢀlowꢀESRꢀ
capacitor.ꢀRegardlessꢀofꢀwhatꢀtypeꢀofꢀbulkꢀcapacitorꢀisꢀ
used,ꢀanꢀadditionalꢀ1µFꢀceramicꢀcapacitorꢀplacedꢀdirectlyꢀ
adjacentꢀtoꢀtheꢀINTV ꢀandꢀPGNDꢀpinsꢀisꢀhighlyꢀrecom-
CC
Significantꢀefficiencyꢀandꢀthermalꢀgainsꢀcanꢀbeꢀrealizedꢀ
mended.ꢀGoodꢀbypassingꢀisꢀneededꢀtoꢀsupplyꢀtheꢀhighꢀ
transientꢀcurrentsꢀrequiredꢀbyꢀtheꢀMOSFETꢀgateꢀdriversꢀ
andꢀtoꢀpreventꢀinteractionꢀbetweenꢀtheꢀchannels.
byꢀpoweringꢀINTV ꢀfromꢀtheꢀoutput,ꢀsinceꢀtheꢀV ꢀcur-
CC
IN
rentꢀresultingꢀfromꢀtheꢀdriverꢀandꢀcontrolꢀcurrentsꢀwillꢀbeꢀ
scaledꢀbyꢀaꢀfactorꢀofꢀ(DutyꢀCycle)/(SwitcherꢀEfficiency).ꢀ
Forꢀ5Vꢀtoꢀ14Vꢀregulatorꢀoutputs,ꢀthisꢀmeansꢀconnectingꢀ
HighꢀinputꢀvoltageꢀapplicationsꢀinꢀwhichꢀlargeꢀMOSFETsꢀareꢀ
beingꢀdrivenꢀatꢀhighꢀfrequenciesꢀmayꢀcauseꢀtheꢀmaximumꢀ
junctionꢀtemperatureꢀratingꢀforꢀtheꢀLTC3858ꢀtoꢀbeꢀexceeded.ꢀ
theꢀEXTV ꢀpinꢀdirectlyꢀtoꢀV .ꢀTyingꢀtheꢀEXTV ꢀpinꢀtoꢀ
CC
OUTꢀ
CC
anꢀ8.5Vꢀsupplyꢀreducesꢀtheꢀjunctionꢀtemperatureꢀinꢀtheꢀ
TheꢀINTV ꢀcurrent,ꢀwhichꢀisꢀdominatedꢀbyꢀtheꢀgateꢀchargeꢀ
CC
previousꢀexampleꢀfromꢀ125°Cꢀto:
current,ꢀmayꢀbeꢀsuppliedꢀbyꢀeitherꢀtheꢀV ꢀLDOꢀorꢀtheꢀ
IN
CC
ꢀ T ꢀ=ꢀ70°Cꢀ+ꢀ(32mA)(8.5V)(43°C/W)ꢀ=ꢀ82°C
J
EXTV ꢀLDO.ꢀWhenꢀtheꢀvoltageꢀonꢀtheꢀEXTV ꢀpinꢀisꢀlessꢀ
CC
thanꢀ4.7V,ꢀtheꢀV ꢀLDOꢀisꢀenabled.ꢀPowerꢀdissipationꢀforꢀtheꢀ
However,ꢀforꢀ3.3Vꢀandꢀotherꢀlowꢀvoltageꢀoutputs,ꢀaddi-
IN
ICꢀinꢀthisꢀcaseꢀisꢀhighestꢀandꢀisꢀequalꢀtoꢀV ꢀ•ꢀI
.ꢀTheꢀ
tionalꢀcircuitryꢀisꢀrequiredꢀtoꢀderiveꢀINTV ꢀpowerꢀfromꢀ
IN INTVCC
CC
gateꢀchargeꢀcurrentꢀisꢀdependentꢀonꢀoperatingꢀfrequencyꢀ
theꢀoutput.
3858fa
ꢁꢀ
LTC3858
applicaTions inForMaTion
Theꢀfollowingꢀlistꢀsummarizesꢀtheꢀfourꢀpossibleꢀconnec-
andꢀturnsꢀitꢀon.ꢀTheꢀswitchꢀnodeꢀvoltage,ꢀSW,ꢀrisesꢀtoꢀV ꢀ
IN
tionsꢀforꢀEXTV :
andꢀtheꢀBOOSTꢀpinꢀfollows.ꢀWithꢀtheꢀtopsideꢀMOSFETꢀ
CC
on,ꢀtheꢀboostꢀvoltageꢀisꢀaboveꢀtheꢀinputꢀsupply:ꢀV
ꢀ=ꢀ
BOOST
1.ꢀꢀEXTV ꢀLeftꢀOpenꢀ(orꢀGrounded).ꢀThisꢀwillꢀcauseꢀINTV ꢀ
CC
CC
V ꢀ+ꢀV
.ꢀTheꢀvalueꢀofꢀtheꢀboostꢀcapacitor,ꢀC ,ꢀneedsꢀ
IN
INTVCC
B
toꢀbeꢀpoweredꢀfromꢀtheꢀinternalꢀ5.1Vꢀregulatorꢀresult-
ingꢀinꢀanꢀefficiencyꢀpenaltyꢀofꢀupꢀtoꢀ10%ꢀatꢀhighꢀinputꢀ
voltages.
toꢀbeꢀ100ꢀtimesꢀthatꢀofꢀtheꢀtotalꢀinputꢀcapacitanceꢀofꢀtheꢀ
topsideꢀMOSFET(s).ꢀTheꢀreverseꢀbreakdownꢀofꢀtheꢀexternalꢀ
SchottkyꢀdiodeꢀmustꢀbeꢀgreaterꢀthanꢀV
.ꢀ
IN(MAX)
2.ꢀꢀEXTV ꢀConnectedꢀDirectlyꢀtoꢀV .ꢀThisꢀisꢀtheꢀnormalꢀ
CC
OUTꢀ
Whenꢀadjustingꢀtheꢀgateꢀdriveꢀlevel,ꢀtheꢀfinalꢀarbiterꢀisꢀtheꢀ
totalꢀinputꢀcurrentꢀforꢀtheꢀregulator.ꢀIfꢀaꢀchangeꢀisꢀmadeꢀ
andꢀtheꢀinputꢀcurrentꢀdecreases,ꢀthenꢀtheꢀefficiencyꢀhasꢀ
improved.ꢀIfꢀthereꢀisꢀnoꢀchangeꢀinꢀinputꢀcurrent,ꢀthenꢀthereꢀ
isꢀnoꢀchangeꢀinꢀefficiency.
connectionꢀforꢀaꢀ5Vꢀtoꢀ14Vꢀregulatorꢀandꢀprovidesꢀtheꢀ
highestꢀefficiency.
3.ꢀꢀEXTV ꢀConnectedꢀtoꢀanꢀExternalꢀSupply.ꢀIfꢀanꢀexternalꢀ
CC
supplyꢀisꢀavailableꢀinꢀtheꢀ5Vꢀtoꢀ14Vꢀrange,ꢀitꢀmayꢀbeꢀ
usedꢀtoꢀpowerꢀEXTV .ꢀEnsureꢀthatꢀEXTV ꢀ<ꢀV .
CC
CC
IN
Fault Conditions: Current Limit and Current Foldback
4.ꢀꢀEXTV ꢀConnectedꢀtoꢀanꢀOutput-DerivedꢀBoostꢀNetwork.ꢀ
CC
Forꢀ3.3Vꢀandꢀotherꢀlowꢀvoltageꢀregulators,ꢀefficiencyꢀ
Whenꢀtheꢀoutputꢀcurrentꢀhitsꢀtheꢀcurrentꢀlimit,ꢀtheꢀoutputꢀ
voltageꢀbeginsꢀtoꢀdrop.ꢀIfꢀtheꢀoutputꢀvoltageꢀfallsꢀbelowꢀ
70%ꢀ ofꢀ itsꢀ nominalꢀ outputꢀ level,ꢀ thenꢀ theꢀ maximumꢀ
senseꢀvoltageꢀisꢀprogressivelyꢀloweredꢀtoꢀaboutꢀhalfꢀofꢀ
itsꢀmaximumꢀselectedꢀvalue.ꢀUnderꢀshort-circuitꢀcondi-
tionsꢀwithꢀveryꢀlowꢀdutyꢀcycles,ꢀtheꢀLTC3858ꢀwillꢀbeginꢀ
cycleꢀskippingꢀinꢀorderꢀtoꢀlimitꢀtheꢀshort-circuitꢀcurrent.ꢀ
InꢀthisꢀsituationꢀtheꢀbottomꢀMOSFETꢀwillꢀbeꢀdissipatingꢀ
mostꢀofꢀtheꢀpowerꢀbutꢀlessꢀthanꢀinꢀnormalꢀoperation.ꢀTheꢀ
short-circuitꢀrippleꢀcurrentꢀisꢀdeterminedꢀbyꢀtheꢀminimumꢀ
gainsꢀcanꢀstillꢀbeꢀrealizedꢀbyꢀconnectingꢀEXTV ꢀtoꢀanꢀ
CC
output-derivedꢀvoltageꢀthatꢀhasꢀbeenꢀboostedꢀtoꢀgreaterꢀ
thanꢀ4.7V.ꢀThisꢀcanꢀbeꢀdoneꢀwithꢀtheꢀcapacitiveꢀchargeꢀ
pumpꢀshownꢀinꢀFigureꢀ8.ꢀEnsureꢀthatꢀEXTV ꢀ<ꢀV .
CC
IN
V
IN
C
IN
BAT85
BAT85
BAT85
V
IN
MTOP
MBOT
on-time,ꢀt
,ꢀofꢀtheꢀLTC3858ꢀ(≈95ns),ꢀtheꢀinputꢀvolt-
ON(MIN)
ageꢀandꢀinductorꢀvalue:
VN2222LL
TG1
1/2 LTC3858
L
R
SENSE
V
OUT
EXTV
SW
CC
IN
V
∆IL(SC) = tON(MIN)
L
ꢀ
C
OUT
D
BG1
Theꢀresultingꢀaverageꢀshort-circuitꢀcurrentꢀis:
3858 F08
PGND
50% •I
1
2
ISC =
LIM(MAX) – ∆IL(SC)
RSENSE
Figure 8. Capacitive Charge Pump for EXTVCC
ꢀ
Fault Conditions: Overvoltage Protection (Crowbar)
Topside MOSFET Driver Supply (C , D )
B
B
Theꢀovervoltageꢀcrowbarꢀisꢀdesignedꢀtoꢀblowꢀaꢀsystemꢀ
inputꢀfuseꢀwhenꢀtheꢀoutputꢀvoltageꢀofꢀtheꢀregulatorꢀrisesꢀ
muchꢀhigherꢀthanꢀnominalꢀlevels.ꢀTheꢀcrowbarꢀcausesꢀhugeꢀ
currentsꢀtoꢀflow,ꢀthatꢀblowꢀtheꢀfuseꢀtoꢀprotectꢀagainstꢀaꢀ
shortedꢀtopꢀMOSFETꢀifꢀtheꢀshortꢀoccursꢀwhileꢀtheꢀcontrol-
lerꢀisꢀoperating.
Externalꢀbootstrapꢀcapacitors,ꢀC ,ꢀconnectedꢀtoꢀtheꢀBOOSTꢀ
B
pinsꢀsupplyꢀtheꢀgateꢀdriveꢀvoltagesꢀforꢀtheꢀtopsideꢀMOSFETs.ꢀ
CapacitorꢀC ꢀinꢀtheꢀFunctionalꢀDiagramꢀisꢀchargedꢀthoughꢀ
B
externalꢀdiodeꢀD ꢀfromꢀINTV ꢀwhenꢀtheꢀSWꢀpinꢀisꢀlow.ꢀ
B
CC
Whenꢀ oneꢀ ofꢀ theꢀ topsideꢀ MOSFETsꢀ isꢀ turnedꢀ on,ꢀ theꢀ
driverꢀplacesꢀtheꢀC ꢀvoltageꢀacrossꢀtheꢀgate-sourceꢀofꢀtheꢀ
B
desiredꢀMOSFET.ꢀThisꢀenhancesꢀtheꢀtopꢀMOSFETꢀswitchꢀ
3858fa
ꢁꢁ
LTC3858
applicaTions inForMaTion
1000
900
800
700
600
500
400
300
200
100
0
Aꢀcomparatorꢀmonitorsꢀtheꢀoutputꢀforꢀovervoltageꢀcondi-
tions.ꢀTheꢀcomparatorꢀdetectsꢀfaultsꢀgreaterꢀthanꢀ10%ꢀ
aboveꢀtheꢀnominalꢀoutputꢀvoltage.ꢀWhenꢀthisꢀconditionꢀ
isꢀsensed,ꢀtheꢀtopꢀMOSFETꢀisꢀturnedꢀoffꢀandꢀtheꢀbottomꢀ
MOSFETꢀisꢀturnedꢀonꢀuntilꢀtheꢀovervoltageꢀconditionꢀisꢀ
cleared.ꢀTheꢀbottomꢀMOSFETꢀremainsꢀonꢀcontinuouslyꢀ
forꢀasꢀlongꢀasꢀtheꢀovervoltageꢀconditionꢀpersists;ꢀifꢀV
returnsꢀtoꢀaꢀsafeꢀlevel,ꢀnormalꢀoperationꢀautomaticallyꢀ
resumes.ꢀ
ꢀ
OUT
AꢀshortedꢀtopꢀMOSFETꢀwillꢀresultꢀinꢀaꢀhighꢀcurrentꢀconditionꢀ
whichꢀwillꢀopenꢀtheꢀsystemꢀfuse.ꢀTheꢀswitchingꢀregulatorꢀ
willꢀregulateꢀproperlyꢀwithꢀaꢀleakyꢀtopꢀMOSFETꢀbyꢀalteringꢀ
theꢀdutyꢀcycleꢀtoꢀaccommodateꢀtheꢀleakage.
15 25 35 45 55 65 75 85 95 105 115 125
FREQ PIN RESISTOR (kΩ)
3858 F09
Figure 9. Relationship Between Oscillator Frequency
and Resistor Value at the FREQ Pin
Phase-Locked Loop and Frequency Synchronization
TheꢀLTC3858ꢀhasꢀanꢀinternalꢀphase-lockedꢀloopꢀ(PLL)ꢀ
comprisedꢀofꢀaꢀphaseꢀfrequencyꢀdetector,ꢀaꢀlowpassꢀfilter,ꢀ
andꢀaꢀvoltage-controlledꢀoscillatorꢀ(VCO).ꢀThisꢀallowsꢀtheꢀ
turn-onꢀofꢀtheꢀtopꢀMOSFETꢀofꢀcontrollerꢀ1ꢀtoꢀbeꢀlockedꢀtoꢀ
theꢀrisingꢀedgeꢀofꢀanꢀexternalꢀclockꢀsignalꢀappliedꢀtoꢀtheꢀ
PLLIN/MODEꢀpin.ꢀTheꢀturn-onꢀofꢀcontrollerꢀ2’sꢀtopꢀMOSFETꢀ
isꢀthusꢀ180ꢀdegreesꢀoutꢀofꢀphaseꢀwithꢀtheꢀexternalꢀclock.ꢀ
Theꢀphaseꢀdetectorꢀisꢀanꢀedgeꢀsensitiveꢀdigitalꢀtypeꢀthatꢀ
providesꢀzeroꢀdegreesꢀphaseꢀshiftꢀbetweenꢀtheꢀexternalꢀ
andꢀinternalꢀoscillators.ꢀThisꢀtypeꢀofꢀphaseꢀdetectorꢀdoesꢀ
notꢀexhibitꢀfalseꢀlockꢀtoꢀharmonicsꢀofꢀtheꢀexternalꢀclock.
NoteꢀthatꢀtheꢀLTC3858ꢀcanꢀonlyꢀbeꢀsynchronizedꢀtoꢀanꢀ
externalꢀ clockꢀ whoseꢀ frequencyꢀ isꢀ withinꢀ rangeꢀ ofꢀ theꢀ
LTC3858’sꢀinternalꢀVCO,ꢀwhichꢀisꢀnominallyꢀ55kHzꢀtoꢀ1MHz.ꢀ
Thisꢀisꢀguaranteedꢀtoꢀbeꢀbetweenꢀ75kHzꢀandꢀ850kHz.ꢀ
Typically,ꢀ theꢀ externalꢀ clockꢀ (onꢀ theꢀ PLLIN/MODEꢀ pin)ꢀ
inputꢀhighꢀthresholdꢀisꢀ1.6V,ꢀwhileꢀtheꢀinputꢀlowꢀthresholdꢀ
isꢀ1.1V.
RapidꢀphaseꢀlockingꢀcanꢀbeꢀachievedꢀbyꢀusingꢀtheꢀFREQꢀ
pinꢀ toꢀ setꢀ aꢀ free-runningꢀ frequencyꢀ nearꢀ theꢀ desiredꢀ
synchronizationꢀfrequency.ꢀTheꢀVCO’sꢀinputꢀvoltageꢀisꢀ
prebiasedꢀatꢀaꢀfrequencyꢀcorrespondingꢀtoꢀtheꢀfrequencyꢀ
setꢀbyꢀtheꢀFREQꢀpin.ꢀOnceꢀprebiased,ꢀtheꢀPLLꢀonlyꢀneedsꢀ
toꢀadjustꢀtheꢀfrequencyꢀslightlyꢀtoꢀachieveꢀphaseꢀlockꢀ
andꢀsynchronization.ꢀAlthoughꢀitꢀisꢀnotꢀrequiredꢀthatꢀtheꢀ
free-runningꢀfrequencyꢀbeꢀnearꢀexternalꢀclockꢀfrequency,ꢀ
doingꢀsoꢀwillꢀpreventꢀtheꢀoperatingꢀfrequencyꢀfromꢀpassingꢀ
throughꢀaꢀlargeꢀrangeꢀofꢀfrequenciesꢀasꢀtheꢀPLLꢀlocks.
Whenꢀnotꢀprebiased,ꢀapplyingꢀanꢀexternalꢀclockꢀwillꢀinvokeꢀ
traditionalꢀPLLꢀoperation.ꢀIfꢀtheꢀexternalꢀclockꢀfrequencyꢀisꢀ
greaterꢀthanꢀtheꢀinternalꢀoscillator’sꢀfrequency,ꢀf ,ꢀthenꢀ
OSC
currentꢀisꢀsourcedꢀcontinuouslyꢀfromꢀtheꢀphaseꢀdetectorꢀ
output,ꢀpullingꢀupꢀtheꢀVCOꢀinput.ꢀWhenꢀtheꢀexternalꢀclockꢀ
frequencyꢀisꢀlessꢀthanꢀf ,ꢀcurrentꢀisꢀsunkꢀcontinuously,ꢀ
OSC
pullingꢀdownꢀtheꢀVCOꢀinput.ꢀIfꢀtheꢀexternalꢀandꢀinternalꢀ
frequenciesꢀareꢀtheꢀsameꢀbutꢀexhibitꢀaꢀphaseꢀdifference,ꢀ
theꢀcurrentꢀsourcesꢀturnꢀonꢀforꢀanꢀamountꢀofꢀtimeꢀcor-
respondingꢀtoꢀtheꢀphaseꢀdifference.ꢀTheꢀvoltageꢀatꢀtheꢀ
VCOꢀinputꢀisꢀadjustedꢀuntilꢀtheꢀphaseꢀandꢀfrequencyꢀofꢀ
theꢀinternalꢀandꢀexternalꢀoscillatorsꢀareꢀidentical.ꢀAtꢀtheꢀ
stableꢀoperatingꢀpoint,ꢀtheꢀphaseꢀdetectorꢀoutputꢀisꢀhighꢀ
Tableꢀ2ꢀsummarizesꢀtheꢀdifferentꢀstatesꢀinꢀwhichꢀtheꢀFREQꢀ
pinꢀcanꢀbeꢀused.
Table 2
FREQ PIN
PLLIN/MODE PIN
DCꢀVoltage
FREQUENCY
350kHz
0V
INTV
DCꢀVoltage
535kHz
CC
impedanceꢀandꢀtheꢀinternalꢀfilterꢀcapacitor,ꢀC ,ꢀholdsꢀtheꢀ
LPꢀ
Resistor
DCꢀVoltage
50kHz–900kHz
voltageꢀatꢀtheꢀVCOꢀinput.
AnyꢀofꢀtheꢀAbove
ExternalꢀClock
Phase–Lockedꢀtoꢀ
ExternalꢀClock
3858fa
ꢁꢂ
LTC3858
applicaTions inForMaTion
Minimum On-Time Considerations
1.ꢀTheꢀV ꢀcurrentꢀisꢀtheꢀDCꢀinputꢀsupplyꢀcurrentꢀgivenꢀ
IN
inꢀtheꢀElectricalꢀCharacteristicsꢀtable,ꢀwhichꢀexcludesꢀ
Minimumꢀon-time,ꢀt
,ꢀisꢀtheꢀsmallestꢀtimeꢀdurationꢀ
ON(MIN)
MOSFETꢀdriverꢀandꢀcontrolꢀcurrents.ꢀV ꢀcurrentꢀtypi-
IN
thatꢀtheꢀLTC3858ꢀisꢀcapableꢀofꢀturningꢀonꢀtheꢀtopꢀMOSFET.ꢀ
callyꢀresultsꢀinꢀaꢀsmallꢀ(<0.1%)ꢀloss.
Itꢀisꢀdeterminedꢀbyꢀinternalꢀtimingꢀdelaysꢀandꢀtheꢀgateꢀ
chargeꢀrequiredꢀtoꢀturnꢀonꢀtheꢀtopꢀMOSFET.ꢀLowꢀdutyꢀ 2.ꢀINTV ꢀcurrentꢀisꢀtheꢀsumꢀofꢀtheꢀMOSFETꢀdriverꢀandꢀ
CC
cycleꢀapplicationsꢀmayꢀapproachꢀthisꢀminimumꢀon-timeꢀ
limitꢀandꢀcareꢀshouldꢀbeꢀtakenꢀtoꢀensureꢀthat:
controlꢀcurrents.ꢀTheꢀMOSFETꢀdriverꢀcurrentꢀresultsꢀ
fromꢀ switchingꢀ theꢀ gateꢀ capacitanceꢀ ofꢀ theꢀ powerꢀ
MOSFETs.ꢀ Eachꢀ timeꢀ aꢀ MOSFETꢀ gateꢀ isꢀ switchedꢀ
fromꢀlowꢀtoꢀhighꢀtoꢀlowꢀagain,ꢀaꢀpacketꢀofꢀcharge,ꢀdQ,ꢀ
VOUT
tON(MIN)
<
V
f
IN
movesꢀfromꢀINTV ꢀtoꢀground.ꢀTheꢀresultingꢀdQ/dtꢀisꢀ
CC
ꢀ
aꢀcurrentꢀoutꢀofꢀINTV ꢀthatꢀisꢀtypicallyꢀmuchꢀlargerꢀ
CC
Ifꢀtheꢀdutyꢀcycleꢀfallsꢀbelowꢀwhatꢀcanꢀbeꢀaccommodatedꢀ
byꢀtheꢀminimumꢀon-time,ꢀtheꢀcontrollerꢀwillꢀbeginꢀtoꢀskipꢀ
cycles.ꢀTheꢀoutputꢀvoltageꢀwillꢀcontinueꢀtoꢀbeꢀregulated,ꢀ
butꢀtheꢀrippleꢀvoltageꢀandꢀcurrentꢀwillꢀincrease.
thanꢀtheꢀcontrolꢀcircuitꢀcurrent.ꢀInꢀcontinuousꢀmode,ꢀ
I
ꢀ=ꢀf(Q ꢀ+ꢀQ ),ꢀwhereꢀQ ꢀandꢀQ ꢀareꢀtheꢀgateꢀ
GATECHG
T B T B
chargesꢀofꢀtheꢀtopsideꢀandꢀbottomꢀsideꢀMOSFETs.
ꢀ SupplyingꢀINTV ꢀfromꢀanꢀoutput-derivedꢀpowerꢀsourceꢀ
CC
Theꢀminimumꢀon-timeꢀforꢀtheꢀLTC3858ꢀisꢀapproximatelyꢀ
95ns.ꢀHowever,ꢀasꢀtheꢀpeakꢀsenseꢀvoltageꢀdecreasesꢀtheꢀ
minimumꢀon-timeꢀgraduallyꢀincreasesꢀupꢀtoꢀaboutꢀ130ns.ꢀ
Thisꢀisꢀofꢀparticularꢀconcernꢀinꢀforcedꢀcontinuousꢀapplica-
tionsꢀwithꢀlowꢀrippleꢀcurrentꢀatꢀlightꢀloads.ꢀIfꢀtheꢀdutyꢀcycleꢀ
dropsꢀbelowꢀtheꢀminimumꢀon-timeꢀlimitꢀinꢀthisꢀsituation,ꢀ
aꢀsignificantꢀamountꢀofꢀcycleꢀskippingꢀcanꢀoccurꢀwithꢀcor-
respondinglyꢀlargerꢀcurrentꢀandꢀvoltageꢀripple.
throughꢀ EXTV ꢀ willꢀ scaleꢀ theꢀ V ꢀ currentꢀ requiredꢀ
CC
IN
forꢀtheꢀdriverꢀandꢀcontrolꢀcircuitsꢀbyꢀaꢀfactorꢀofꢀ(Dutyꢀ
Cycle)/(Efficiency).ꢀForꢀexample,ꢀinꢀaꢀ20Vꢀtoꢀ5Vꢀapplica-
tion,ꢀ10mAꢀofꢀINTV ꢀcurrentꢀresultsꢀinꢀapproximatelyꢀ
CC
2.5mAꢀofꢀV ꢀcurrent.ꢀThisꢀreducesꢀtheꢀmidcurrentꢀlossꢀ
IN
fromꢀ10%ꢀorꢀmoreꢀ(ifꢀtheꢀdriverꢀwasꢀpoweredꢀdirectlyꢀ
fromꢀV )ꢀtoꢀonlyꢀaꢀfewꢀpercent.
IN
2
3.ꢀI RꢀlossesꢀareꢀpredictedꢀfromꢀtheꢀDCꢀresistancesꢀofꢀtheꢀ
fuseꢀ(ifꢀused),ꢀMOSFET,ꢀinductor,ꢀcurrentꢀsenseꢀresis-
tor,ꢀandꢀinputꢀandꢀoutputꢀcapacitorꢀESR.ꢀInꢀcontinuousꢀ
modeꢀtheꢀaverageꢀoutputꢀcurrentꢀflowsꢀthroughꢀLꢀandꢀ
Efficiency Considerations
Theꢀpercentꢀefficiencyꢀofꢀaꢀswitchingꢀregulatorꢀisꢀequalꢀtoꢀ
theꢀoutputꢀpowerꢀdividedꢀbyꢀtheꢀinputꢀpowerꢀtimesꢀ100%.ꢀ
Itꢀisꢀoftenꢀusefulꢀtoꢀanalyzeꢀindividualꢀlossesꢀtoꢀdetermineꢀ
whatꢀisꢀlimitingꢀtheꢀefficiencyꢀandꢀwhichꢀchangeꢀwouldꢀ
produceꢀtheꢀmostꢀimprovement.ꢀPercentꢀefficiencyꢀcanꢀ
beꢀexpressedꢀas:
R
,ꢀbutꢀisꢀ“chopped”ꢀbetweenꢀtheꢀtopsideꢀMOSFETꢀ
SENSE
andꢀtheꢀsynchronousꢀMOSFET.ꢀIfꢀtheꢀtwoꢀMOSFETsꢀhaveꢀ
approximatelyꢀtheꢀsameꢀR
,ꢀthenꢀtheꢀresistanceꢀ
DS(ON)
ofꢀoneꢀMOSFETꢀcanꢀsimplyꢀbeꢀsummedꢀwithꢀtheꢀresis-
2
tancesꢀofꢀL,ꢀR
ꢀandꢀESRꢀtoꢀobtainꢀI Rꢀlosses.ꢀForꢀ
DS(ON)
SENSE
example,ꢀifꢀeachꢀR
ꢀ=ꢀ30mΩ,ꢀR ꢀ=ꢀ50mΩ,ꢀR
ꢀ
ꢀ %Efficiencyꢀ=ꢀ100%ꢀ–ꢀ(L1ꢀ+ꢀL2ꢀ+ꢀL3ꢀ+ꢀ...)
L
SENSE
=ꢀ10mΩꢀandꢀR ꢀ=ꢀ40mΩꢀ(sumꢀofꢀbothꢀinputꢀandꢀ
ESR
whereꢀL1,ꢀL2,ꢀetc.ꢀareꢀtheꢀindividualꢀlossesꢀasꢀaꢀpercent-
ageꢀofꢀinputꢀpower.
outputꢀcapacitanceꢀlosses),ꢀthenꢀtheꢀtotalꢀresistanceꢀ
isꢀ130mΩ.ꢀThisꢀresultsꢀinꢀlossesꢀrangingꢀfromꢀ3%ꢀtoꢀ
13%ꢀasꢀtheꢀoutputꢀcurrentꢀincreasesꢀfromꢀ1Aꢀtoꢀ5Aꢀforꢀ
aꢀ5Vꢀoutput,ꢀorꢀaꢀ4%ꢀtoꢀ20%ꢀlossꢀforꢀaꢀ3.3Vꢀoutput.ꢀ
Althoughꢀallꢀdissipativeꢀelementsꢀinꢀtheꢀcircuitꢀproduceꢀ
losses,ꢀfourꢀmainꢀsourcesꢀusuallyꢀaccountꢀforꢀmostꢀofꢀtheꢀ
lossesꢀinꢀLTC3858ꢀcircuits:ꢀ1)ꢀICꢀV ꢀcurrent,ꢀ2)ꢀINTV ꢀ
EfficiencyꢀvariesꢀasꢀtheꢀinverseꢀsquareꢀofꢀV ꢀforꢀtheꢀ
IN
CC
OUT
2
regulatorꢀ current,ꢀ 3)ꢀ I Rꢀ losses,ꢀ 4)ꢀ topsideꢀ MOSFETꢀ
sameꢀexternalꢀcomponentsꢀandꢀoutputꢀpowerꢀlevel.ꢀTheꢀ
transitionꢀlosses.
3858fa
ꢁꢃ
LTC3858
applicaTions inForMaTion
it also provides a DC coupled and AC filtered closed-loop
response test point. The DC step, rise time and settling
at this test point truly reflects the closed-loop response.ꢀ
Assumingꢀaꢀpredominantlyꢀsecondꢀorderꢀsystem,ꢀphaseꢀ
marginꢀand/orꢀdampingꢀfactorꢀcanꢀbeꢀestimatedꢀusingꢀtheꢀ
percentageꢀofꢀovershootꢀseenꢀatꢀthisꢀpin.ꢀTheꢀbandwidthꢀ
canꢀalsoꢀbeꢀestimatedꢀbyꢀexaminingꢀtheꢀriseꢀtimeꢀatꢀtheꢀ
pin.ꢀTheꢀITHꢀexternalꢀcomponentsꢀshownꢀinꢀFigureꢀ12ꢀ
circuitꢀwillꢀprovideꢀanꢀadequateꢀstartingꢀpointꢀforꢀmostꢀ
applications.
combinedꢀeffectsꢀofꢀincreasinglyꢀlowerꢀoutputꢀvoltagesꢀ
andꢀhigherꢀcurrentsꢀrequiredꢀbyꢀhighꢀperformanceꢀdigitalꢀ
systemsꢀisꢀnotꢀdoublingꢀbutꢀquadruplingꢀtheꢀimportanceꢀ
ofꢀlossꢀtermsꢀinꢀtheꢀswitchingꢀregulatorꢀsystem!
4.ꢀꢀTransitionꢀlossesꢀapplyꢀonlyꢀtoꢀtheꢀtopsideꢀMOSFET(s),ꢀ
andꢀbecomeꢀsignificantꢀonlyꢀwhenꢀoperatingꢀatꢀhighꢀ
inputꢀ voltagesꢀ (typicallyꢀ 15Vꢀ orꢀ greater).ꢀ Transitionꢀ
lossesꢀcanꢀbeꢀestimatedꢀfrom:
ꢀ ꢀ TransitionꢀLossꢀ=ꢀ(1.7)ꢀ•ꢀV ꢀ•ꢀ2ꢀ•ꢀI
ꢀ•ꢀC ꢀ•ꢀf
O(MAX) RSS
IN
ꢀ Otherꢀ“hidden”ꢀlossesꢀsuchꢀasꢀcopperꢀtraceꢀandꢀinternalꢀ
batteryꢀresistancesꢀcanꢀaccountꢀforꢀanꢀadditionalꢀ5%ꢀtoꢀ
10%ꢀefficiencyꢀdegradationꢀinꢀportableꢀsystems.ꢀItꢀisꢀ
veryꢀimportantꢀtoꢀincludeꢀtheseꢀ“system”ꢀlevelꢀlossesꢀ
duringꢀtheꢀdesignꢀphase.ꢀTheꢀinternalꢀbatteryꢀandꢀfuseꢀ
resistanceꢀlossesꢀcanꢀbeꢀminimizedꢀbyꢀmakingꢀsureꢀthatꢀ
TheꢀI ꢀseriesꢀR -C ꢀfilterꢀsetsꢀtheꢀdominantꢀpole-zeroꢀ
TH
C
C
loopꢀcompensation.ꢀTheꢀvaluesꢀcanꢀbeꢀmodifiedꢀslightlyꢀ
(fromꢀ0.5ꢀtoꢀ2ꢀtimesꢀtheirꢀsuggestedꢀvalues)ꢀtoꢀoptimizeꢀ
transientꢀresponseꢀonceꢀtheꢀfinalꢀPCꢀlayoutꢀisꢀdoneꢀandꢀ
theꢀparticularꢀoutputꢀcapacitorꢀtypeꢀandꢀvalueꢀhaveꢀbeenꢀ
determined.ꢀTheꢀoutputꢀcapacitorsꢀneedꢀtoꢀbeꢀselectedꢀ
becauseꢀtheꢀvariousꢀtypesꢀandꢀvaluesꢀdetermineꢀtheꢀloopꢀ
gainꢀandꢀphase.ꢀAnꢀoutputꢀcurrentꢀpulseꢀofꢀ20%ꢀtoꢀ80%ꢀ
ofꢀfull-loadꢀcurrentꢀhavingꢀaꢀriseꢀtimeꢀofꢀ1µsꢀtoꢀ10µsꢀwillꢀ
C ꢀhasꢀadequateꢀchargeꢀstorageꢀandꢀveryꢀlowꢀESRꢀatꢀ
IN
theꢀswitchingꢀfrequency.ꢀAꢀ25Wꢀsupplyꢀwillꢀtypicallyꢀ
requireꢀ aꢀ minimumꢀ ofꢀ 20µFꢀ toꢀ 40µFꢀ ofꢀ capacitanceꢀ
havingꢀaꢀmaximumꢀofꢀ20mΩꢀtoꢀ50mΩꢀofꢀESR.ꢀTheꢀ
LTC3858ꢀ2-phaseꢀarchitectureꢀtypicallyꢀhalvesꢀthisꢀinputꢀ
capacitanceꢀ requirementꢀ overꢀ competingꢀ solutions.ꢀ
Otherꢀ lossesꢀ includingꢀ Schottkyꢀ conductionꢀ lossesꢀ
duringꢀdead-timeꢀandꢀinductorꢀcoreꢀlossesꢀgenerallyꢀ
accountꢀforꢀlessꢀthanꢀ2%ꢀtotalꢀadditionalꢀloss.
produceꢀoutputꢀvoltageꢀandꢀI ꢀpinꢀwaveformsꢀthatꢀwillꢀ
TH
giveꢀaꢀsenseꢀofꢀtheꢀoverallꢀloopꢀstabilityꢀwithoutꢀbreakingꢀ
theꢀfeedbackꢀloop.ꢀ
Placingꢀ aꢀ resistiveꢀ loadꢀ andꢀ aꢀ powerꢀ MOSFETꢀ directlyꢀ
acrossꢀtheꢀoutputꢀcapacitorꢀandꢀdrivingꢀtheꢀgateꢀwithꢀanꢀ
appropriateꢀsignalꢀgeneratorꢀisꢀaꢀpracticalꢀwayꢀtoꢀproduceꢀ
aꢀrealisticꢀloadꢀstepꢀcondition.ꢀTheꢀinitialꢀoutputꢀvoltageꢀ
stepꢀresultingꢀfromꢀtheꢀstepꢀchangeꢀinꢀoutputꢀcurrentꢀmayꢀ
notꢀbeꢀwithinꢀtheꢀbandwidthꢀofꢀtheꢀfeedbackꢀloop,ꢀsoꢀthisꢀ
signalꢀcannotꢀbeꢀusedꢀtoꢀdetermineꢀphaseꢀmargin.ꢀThisꢀ
Checking Transient Response
Theꢀregulatorꢀloopꢀresponseꢀcanꢀbeꢀcheckedꢀbyꢀlookingꢀatꢀ
theꢀloadꢀcurrentꢀtransientꢀresponse.ꢀSwitchingꢀregulatorsꢀ
takeꢀseveralꢀcyclesꢀtoꢀrespondꢀtoꢀaꢀstepꢀinꢀDCꢀ(resistive)ꢀ
loadꢀcurrent.ꢀWhenꢀaꢀloadꢀstepꢀoccurs,ꢀVOUTꢀshiftsꢀbyꢀ
anꢀamountꢀequalꢀtoꢀ∆ILOADꢀ(ESR),ꢀwhereꢀESRꢀisꢀtheꢀef-
fectiveꢀseriesꢀresistanceꢀofꢀCOUTꢀ.ꢀ∆ILOADꢀalsoꢀbeginsꢀtoꢀ
chargeꢀorꢀdischargeꢀCOUTꢀgeneratingꢀtheꢀfeedbackꢀerrorꢀ
signalꢀthatꢀforcesꢀtheꢀregulatorꢀtoꢀadaptꢀtoꢀtheꢀcurrentꢀ
changeꢀandꢀreturnꢀVOUTꢀtoꢀitsꢀsteady-stateꢀvalue.ꢀDuringꢀ
thisꢀrecoveryꢀtimeꢀVOUTꢀcanꢀbeꢀmonitoredꢀforꢀexcessiveꢀ
overshootꢀorꢀ ringing,ꢀ whichꢀ wouldꢀindicateꢀ aꢀ stabilityꢀ
problem.ꢀOPTI-LOOPꢀcompensationꢀallowsꢀtheꢀtransientꢀ
responseꢀtoꢀbeꢀoptimizedꢀoverꢀaꢀwideꢀrangeꢀofꢀoutputꢀ
capacitanceꢀandꢀESRꢀvalues.ꢀThe availability of the ITH pin
not only allows optimization of control loop behavior, but
isꢀwhyꢀitꢀisꢀbetterꢀtoꢀlookꢀatꢀtheꢀI ꢀpinꢀsignalꢀwhichꢀisꢀinꢀ
TH
theꢀfeedbackꢀloopꢀandꢀisꢀtheꢀfilteredꢀandꢀcompensatedꢀ
controlꢀloopꢀresponse.ꢀ
TheꢀgainꢀofꢀtheꢀloopꢀwillꢀbeꢀincreasedꢀbyꢀincreasingꢀR ꢀ
C
andꢀtheꢀbandwidthꢀofꢀtheꢀloopꢀwillꢀbeꢀincreasedꢀbyꢀde-
creasingꢀC .ꢀIfꢀR ꢀisꢀincreasedꢀbyꢀtheꢀsameꢀfactorꢀthatꢀC ꢀ
C
C
C
isꢀdecreased,ꢀtheꢀzeroꢀfrequencyꢀwillꢀbeꢀkeptꢀtheꢀsame,ꢀ
therebyꢀkeepingꢀtheꢀphaseꢀshiftꢀtheꢀsameꢀinꢀtheꢀmostꢀ
criticalꢀfrequencyꢀrangeꢀofꢀtheꢀfeedbackꢀloop.ꢀTheꢀoutputꢀ
voltageꢀsettlingꢀbehaviorꢀisꢀrelatedꢀtoꢀtheꢀstabilityꢀofꢀtheꢀ
closed-loopꢀsystemꢀandꢀwillꢀdemonstrateꢀtheꢀactualꢀoverallꢀ
supplyꢀperformance.
3858fa
ꢁꢄ
LTC3858
applicaTions inForMaTion
Aꢀsecond,ꢀmoreꢀsevereꢀtransientꢀisꢀcausedꢀbyꢀswitchingꢀ
inꢀloadsꢀwithꢀlargeꢀ(>1µF)ꢀsupplyꢀbypassꢀcapacitors.ꢀTheꢀ
dischargedꢀbypassꢀcapacitorsꢀareꢀeffectivelyꢀputꢀinꢀparallelꢀ
Choosingꢀ0.5%ꢀresistors:ꢀR ꢀ=ꢀ24.9kꢀandꢀR ꢀ=ꢀ77.7kꢀyieldsꢀ
A
B
anꢀoutputꢀvoltageꢀofꢀ3.296V.
TheꢀpowerꢀdissipationꢀonꢀtheꢀtopsideꢀMOSFETꢀcanꢀbeꢀeasilyꢀ
estimated.ꢀChoosingꢀaꢀFairchildꢀFDS6982SꢀdualꢀMOSFETꢀ
withꢀC ,ꢀcausingꢀaꢀrapidꢀdropꢀinꢀV .ꢀNoꢀregulatorꢀcanꢀ
OUTꢀ
OUTꢀ
alterꢀitsꢀdeliveryꢀofꢀcurrentꢀquicklyꢀenoughꢀtoꢀpreventꢀthisꢀ
suddenꢀstepꢀchangeꢀinꢀoutputꢀvoltageꢀifꢀtheꢀloadꢀswitchꢀ
resistanceꢀisꢀlowꢀandꢀitꢀisꢀdrivenꢀquickly.ꢀIfꢀtheꢀratioꢀofꢀ
resultsꢀin:ꢀR
ꢀ=ꢀ0.035Ω/0.022Ω,ꢀC
ꢀ=ꢀ215pF.ꢀAtꢀ
DS(ON)
MILLER
maximumꢀinputꢀvoltageꢀwithꢀT(estimated)ꢀ=ꢀ50°C:
2
C
LOAD
ꢀtoꢀC ꢀisꢀgreaterꢀthanꢀ1:50,ꢀtheꢀswitchꢀriseꢀtimeꢀ
3.3V
22V
OUT
PMAIN
=
5A 1+ 0.005 50°C – 25°C
(
)
(
)(
)
shouldꢀbeꢀcontrolledꢀsoꢀthatꢀtheꢀloadꢀriseꢀtimeꢀisꢀlimitedꢀ
toꢀapproximatelyꢀ25ꢀ•ꢀC .ꢀThusꢀaꢀ10µFꢀcapacitorꢀwouldꢀ
LOAD
2 5A
0.035Ω + 22V
2.5Ω 215pF •
(
) (
)
1
(
)(
)
requireꢀaꢀ250µsꢀriseꢀtime,ꢀlimitingꢀtheꢀchargingꢀcurrentꢀ
toꢀaboutꢀ200mA.
2
1
+
350kHz = 331mW
(
)
5V – 2.3V 2.3V
Design Example
ꢀ
Asꢀ aꢀ designꢀ exampleꢀ forꢀ oneꢀ channel,ꢀ assumeꢀ V ꢀ =ꢀ
IN
Aꢀshort-circuitꢀtoꢀgroundꢀwillꢀresultꢀinꢀaꢀfoldedꢀbackꢀcur-
rentꢀof:
12V(nominal),ꢀV ꢀ=ꢀ22Vꢀ(max),ꢀV ꢀ=ꢀ3.3V,ꢀI ꢀ=ꢀ5A,ꢀ
IN
OUT
MAX
V
ꢀ=ꢀ75mVꢀandꢀfꢀ=ꢀ350kHz.
SENSE(MAX)
95ns 22V
(
)
32mV
0.015Ω 2
1
Theꢀinductanceꢀvalueꢀisꢀchosenꢀfirstꢀbasedꢀonꢀaꢀ30%ꢀrippleꢀ
currentꢀassumption.ꢀTheꢀhighestꢀvalueꢀofꢀrippleꢀcurrentꢀ
occursꢀatꢀtheꢀmaximumꢀinputꢀvoltage.ꢀTieꢀtheꢀFREQꢀpinꢀ
toꢀ GND,ꢀ generatingꢀ 350kHzꢀ operation.ꢀ Theꢀ minimumꢀ
inductanceꢀforꢀ30%ꢀrippleꢀcurrentꢀis:
ISC =
–
= 2.98A
4.7µH
ꢀ
withꢀaꢀtypicalꢀvalueꢀofꢀR
ꢀandꢀδꢀ=ꢀ(0.005/°C)(25°C)ꢀ
DS(ON)
=ꢀ0.125.ꢀTheꢀresultingꢀpowerꢀdissipatedꢀinꢀtheꢀbottomꢀ
MOSFETꢀis:
VOUT
f L
VOUT
∆IL =
1–
2
V
PSYNC = 2.98A 1.125 0.022Ω = 220mW
IN
ꢀ
ꢀ
whichꢀisꢀlessꢀthanꢀfull-loadꢀconditions.
Aꢀ4.7µHꢀinductorꢀwillꢀproduceꢀ29%ꢀrippleꢀcurrent.ꢀTheꢀ
peakꢀinductorꢀcurrentꢀwillꢀbeꢀtheꢀmaximumꢀDCꢀvalueꢀplusꢀ
oneꢀhalfꢀtheꢀrippleꢀcurrent,ꢀorꢀ5.73A.ꢀIncreasingꢀtheꢀrippleꢀ
currentꢀwillꢀalsoꢀhelpꢀensureꢀthatꢀtheꢀminimumꢀon-timeꢀ
ofꢀ95nsꢀisꢀnotꢀviolated.ꢀTheꢀminimumꢀon-timeꢀoccursꢀatꢀ
C ꢀisꢀchosenꢀforꢀanꢀRMSꢀcurrentꢀratingꢀofꢀatꢀleastꢀ3Aꢀatꢀ
IN
temperatureꢀassumingꢀonlyꢀthisꢀchannelꢀisꢀon.ꢀC ꢀisꢀ
OUT
chosenꢀwithꢀanꢀESRꢀofꢀ0.02Ωꢀforꢀlowꢀoutputꢀrippleꢀvolt-
age.ꢀTheꢀoutputꢀrippleꢀinꢀcontinuousꢀmodeꢀwillꢀbeꢀhighestꢀ
atꢀtheꢀmaximumꢀinputꢀvoltage.ꢀTheꢀoutputꢀvoltageꢀrippleꢀ
dueꢀtoꢀESRꢀisꢀapproximately:
maximumꢀV :
IN
VOUT
3.3V
tON(MIN)
=
=
= 429ns
V
f
22V 350kHz
ꢀ V ꢀ=ꢀR ꢀ(∆I )ꢀ=ꢀ0.02Ω(1.45A)ꢀ=ꢀ29mV
ORIPPLE ESR L P-P
IN
ꢀ
TheꢀequivalentꢀR
ꢀresistorꢀvalueꢀcanꢀbeꢀcalculatedꢀbyꢀ
SENSE
usingꢀtheꢀminimumꢀvalueꢀforꢀtheꢀmaximumꢀcurrentꢀsenseꢀ
thresholdꢀ(64mV):
64mV
5.73A
RSENSE
≤
= 0.011Ω
ꢀ
3858fa
ꢁꢅ
LTC3858
applicaTions inForMaTion
PC Board Layout Checklist
6.ꢀKeepꢀtheꢀswitchingꢀnodesꢀ(SW1,ꢀSW2),ꢀtopꢀgateꢀnodesꢀ
(TG1,ꢀTG2),ꢀandꢀboostꢀnodesꢀ(BOOST1,ꢀBOOST2)ꢀawayꢀ
fromꢀ sensitiveꢀ small-signalꢀ nodes,ꢀ especiallyꢀ fromꢀ
theꢀoppositesꢀchannel’sꢀvoltageꢀandꢀcurrentꢀsensingꢀ
feedbackꢀpins.ꢀAllꢀofꢀtheseꢀnodesꢀhaveꢀveryꢀlargeꢀandꢀ
fastꢀmovingꢀsignalsꢀandꢀthereforeꢀshouldꢀbeꢀkeptꢀonꢀ
theꢀ“outputꢀside”ꢀofꢀtheꢀLTC3858ꢀandꢀoccupyꢀminimumꢀ
PCꢀtraceꢀarea.
Whenꢀlayingꢀoutꢀtheꢀprintedꢀcircuitꢀboard,ꢀtheꢀfollowingꢀ
checklistꢀshouldꢀbeꢀusedꢀtoꢀensureꢀproperꢀoperationꢀofꢀ
theꢀIC.ꢀTheseꢀitemsꢀareꢀalsoꢀillustratedꢀgraphicallyꢀinꢀtheꢀ
layoutꢀdiagramꢀofꢀFigureꢀ10.ꢀFigureꢀ11ꢀillustratesꢀtheꢀcurrentꢀ
waveformsꢀpresentꢀinꢀtheꢀvariousꢀbranchesꢀofꢀtheꢀ2-phaseꢀ
synchronousꢀregulatorsꢀoperatingꢀinꢀtheꢀcontinuousꢀmode.ꢀ
Checkꢀtheꢀfollowingꢀinꢀyourꢀlayout:
7.ꢀUseꢀaꢀmodifiedꢀ“starꢀground”ꢀtechnique:ꢀaꢀlowꢀimped-
ance,ꢀ largeꢀ copperꢀ areaꢀ centralꢀ groundingꢀ pointꢀ onꢀ
theꢀsameꢀsideꢀofꢀtheꢀPCꢀboardꢀasꢀtheꢀinputꢀandꢀoutputꢀ
1.ꢀꢀAreꢀtheꢀtopꢀN-channelꢀMOSFETsꢀMTOP1ꢀandꢀMTOP2ꢀ
locatedꢀwithinꢀ1cmꢀofꢀeachꢀotherꢀwithꢀaꢀcommonꢀdrainꢀ
connectionꢀatꢀC ?ꢀDoꢀnotꢀattemptꢀtoꢀsplitꢀtheꢀinputꢀ
IN
capacitorsꢀwithꢀtie-insꢀforꢀtheꢀbottomꢀofꢀtheꢀINTV ꢀ
CC
decouplingꢀforꢀtheꢀtwoꢀchannelsꢀasꢀitꢀcanꢀcauseꢀaꢀlargeꢀ
resonantꢀloop.
decouplingꢀcapacitor,ꢀtheꢀbottomꢀofꢀtheꢀvoltageꢀfeedbackꢀ
resistiveꢀdividerꢀandꢀtheꢀSGNDꢀpinꢀofꢀtheꢀIC.
2.ꢀꢀAreꢀtheꢀsignalꢀandꢀpowerꢀgroundsꢀkeptꢀseparate?ꢀTheꢀ
combinedꢀICꢀsignalꢀgroundꢀpinꢀandꢀtheꢀgroundꢀreturnꢀ
PC Board Layout Debugging
ofꢀC
ꢀmustꢀreturnꢀtoꢀtheꢀcombinedꢀC ꢀ(–)ꢀter-
INTVCC
OUT
Startꢀwithꢀoneꢀcontrollerꢀonꢀatꢀaꢀtime.ꢀItꢀisꢀhelpfulꢀtoꢀuseꢀ
aꢀDC-50MHzꢀcurrentꢀprobeꢀtoꢀmonitorꢀtheꢀcurrentꢀinꢀtheꢀ
inductorꢀ whileꢀ testingꢀ theꢀ circuit.ꢀ Monitorꢀ theꢀ outputꢀ
switchingꢀnodeꢀ(SWꢀpin)ꢀtoꢀsynchronizeꢀtheꢀoscilloscopeꢀ
toꢀ theꢀ internalꢀ oscillatorꢀ andꢀ probeꢀ theꢀ actualꢀ outputꢀ
voltageꢀasꢀwell.ꢀCheckꢀforꢀproperꢀperformanceꢀoverꢀtheꢀ
operatingꢀvoltageꢀandꢀcurrentꢀrangeꢀexpectedꢀinꢀtheꢀap-
plication.ꢀTheꢀfrequencyꢀofꢀoperationꢀshouldꢀbeꢀmaintainedꢀ
overꢀtheꢀinputꢀvoltageꢀrangeꢀdownꢀtoꢀdropoutꢀandꢀuntilꢀ
theꢀoutputꢀloadꢀdropsꢀbelowꢀtheꢀlowꢀcurrentꢀoperationꢀ
threshold—typicallyꢀ 10%ꢀ ofꢀ theꢀ maximumꢀ designedꢀ
currentꢀlevelꢀinꢀBurstꢀModeꢀoperation.
minals.ꢀTheꢀpathꢀformedꢀbyꢀtheꢀtopꢀN-channelꢀMOSFET,ꢀ
SchottkyꢀdiodeꢀandꢀtheꢀC ꢀcapacitorꢀshouldꢀhaveꢀshortꢀ
IN
leadsꢀandꢀPCꢀtraceꢀlengths.ꢀTheꢀoutputꢀcapacitorꢀ(–)ꢀ
terminalsꢀshouldꢀbeꢀconnectedꢀasꢀcloseꢀasꢀpossibleꢀ
toꢀtheꢀ(–)ꢀterminalsꢀofꢀtheꢀinputꢀcapacitorꢀbyꢀplacingꢀ
theꢀcapacitorsꢀnextꢀtoꢀeachꢀotherꢀandꢀawayꢀfromꢀtheꢀ
Schottkyꢀloopꢀdescribedꢀabove.
3.ꢀꢀDoꢀtheꢀLTC3858ꢀV ꢀpins’ꢀresistiveꢀdividersꢀconnectꢀtoꢀ
FB
theꢀ(+)ꢀterminalsꢀofꢀC ?ꢀTheꢀresistiveꢀdividerꢀmustꢀbeꢀ
OUT
connectedꢀbetweenꢀtheꢀ(+)ꢀterminalꢀofꢀC ꢀandꢀsignalꢀ
OUT
ground.ꢀTheꢀfeedbackꢀresistorꢀconnectionsꢀshouldꢀnotꢀ
beꢀalongꢀtheꢀhighꢀcurrentꢀinputꢀfeedsꢀfromꢀtheꢀinputꢀ
capacitor(s).
Theꢀdutyꢀcycleꢀpercentageꢀshouldꢀbeꢀmaintainedꢀfromꢀcycleꢀ
toꢀcycleꢀinꢀaꢀwell-designed,ꢀlowꢀnoiseꢀPCBꢀimplementation.ꢀ
Variationꢀinꢀtheꢀdutyꢀcycleꢀatꢀaꢀsubharmonicꢀrateꢀcanꢀsug-
gestꢀnoiseꢀpickupꢀatꢀtheꢀcurrentꢀorꢀvoltageꢀsensingꢀinputsꢀ
orꢀinadequateꢀloopꢀcompensation.ꢀOvercompensationꢀofꢀ
theꢀloopꢀcanꢀbeꢀusedꢀtoꢀtameꢀaꢀpoorꢀPCꢀlayoutꢀifꢀregula-
torꢀ bandwidthꢀ optimizationꢀ isꢀ notꢀ required.ꢀ Onlyꢀ afterꢀ
eachꢀcontrollerꢀisꢀcheckedꢀforꢀitsꢀindividualꢀperformanceꢀ
shouldꢀbothꢀcontrollersꢀbeꢀturnedꢀonꢀatꢀtheꢀsameꢀtime.ꢀ
Aꢀparticularlyꢀdifficultꢀregionꢀofꢀoperationꢀisꢀwhenꢀoneꢀ
controllerꢀchannelꢀisꢀnearingꢀitsꢀcurrentꢀcomparatorꢀtripꢀ
pointꢀwhenꢀtheꢀotherꢀchannelꢀisꢀturningꢀonꢀitsꢀtopꢀMOSFET.ꢀ
Thisꢀoccursꢀaroundꢀ50%ꢀdutyꢀcycleꢀonꢀeitherꢀchannelꢀdueꢀ
toꢀtheꢀphasingꢀofꢀtheꢀinternalꢀclocksꢀandꢀmayꢀcauseꢀminorꢀ
dutyꢀcycleꢀjitter.
–
+
4.ꢀꢀAreꢀtheꢀSENSE ꢀandꢀSENSE ꢀleadsꢀroutedꢀtogetherꢀwithꢀ
minimumꢀPCꢀtraceꢀspacing?ꢀTheꢀfilterꢀcapacitorꢀbetweenꢀ
+
–
SENSE ꢀandꢀSENSE ꢀshouldꢀbeꢀasꢀcloseꢀasꢀpossibleꢀ
toꢀtheꢀIC.ꢀEnsureꢀaccurateꢀcurrentꢀsensingꢀwithꢀKelvinꢀ
connectionsꢀatꢀtheꢀSENSEꢀresistor.
5.ꢀIsꢀtheꢀINTV ꢀdecouplingꢀcapacitorꢀconnectedꢀcloseꢀ
CC
toꢀtheꢀIC,ꢀbetweenꢀtheꢀINTV ꢀandꢀtheꢀpowerꢀgroundꢀ
CC
pins?ꢀThisꢀcapacitorꢀcarriesꢀtheꢀMOSFETꢀdrivers’ꢀcur-
rentꢀpeaks.ꢀAnꢀadditionalꢀ1µFꢀceramicꢀcapacitorꢀplacedꢀ
immediatelyꢀnextꢀtoꢀtheꢀINTV ꢀandꢀPGNDꢀpinsꢀcanꢀhelpꢀ
CC
improveꢀnoiseꢀperformanceꢀsubstantially.
3858fa
ꢁꢆ
LTC3858
applicaTions inForMaTion
R
SS1
PU2
V
PULL-UP
LTC3858
(<6V)
PGOOD2
I
PGOOD2
PGOOD1
TG1
R
TH1
PU1
V
PULL-UP
(<6V)
V
PGOOD1
FB1
L1
R
SENSE
+
–
V
SENSE1
SENSE1
FREQ
OUT1
SW1
C
B1
M1
M2
D1
BOOST1
BG1
PHASMD
CLKOUT
PLLIN/MODE
RUN1
C
C
OUT1
V
IN
f
1µF
CERAMIC
IN
R
C
VIN
IN
PGND
GND
RUN2
EXTV
CC
V
OUT1
C
IN
C
SGND
INTVCC
V
IN
–
INTV
CC
SENSE2
OUT2
D2
1µF
CERAMIC
+
BG2
SENSE2
M4
M3
BOOST2
V
FB2
TH2
C
B2
SW2
TG2
I
R
SENSE
V
OUT2
SS2
L2
3858 F10
Figure 10. Recommended Printed Circuit Layout Diagram
Reduceꢀ V ꢀ fromꢀ itsꢀ nominalꢀ levelꢀ toꢀ verifyꢀ operationꢀ andꢀpossiblyꢀBGꢀconnectionsꢀandꢀtheꢀsensitiveꢀvoltageꢀ
IN
ofꢀtheꢀregulatorꢀinꢀdropout.ꢀCheckꢀtheꢀoperationꢀofꢀtheꢀ andꢀcurrentꢀpins.ꢀTheꢀcapacitorꢀplacedꢀacrossꢀtheꢀcurrentꢀ
undervoltageꢀlockoutꢀcircuitꢀbyꢀfurtherꢀloweringꢀV ꢀwhileꢀ sensingꢀpinsꢀneedsꢀtoꢀbeꢀplacedꢀimmediatelyꢀadjacentꢀtoꢀ
IN
monitoringꢀtheꢀoutputsꢀtoꢀverifyꢀoperation.
theꢀpinsꢀofꢀtheꢀIC.ꢀThisꢀcapacitorꢀhelpsꢀtoꢀminimizeꢀtheꢀ
effectsꢀofꢀdifferentialꢀnoiseꢀinjectionꢀdueꢀtoꢀhighꢀfrequencyꢀ
capacitiveꢀ coupling.ꢀ Ifꢀ problemsꢀ areꢀ encounteredꢀ withꢀ
highꢀcurrentꢀoutputꢀloadingꢀatꢀlowerꢀinputꢀvoltages,ꢀlookꢀ
Investigateꢀwhetherꢀanyꢀproblemsꢀexistꢀonlyꢀatꢀhigherꢀout-
putꢀcurrentsꢀorꢀonlyꢀatꢀhigherꢀinputꢀvoltages.ꢀIfꢀproblemsꢀ
coincideꢀwithꢀhighꢀinputꢀvoltagesꢀandꢀlowꢀoutputꢀcurrents,ꢀ
lookꢀforꢀcapacitiveꢀcouplingꢀbetweenꢀtheꢀBOOST,ꢀSW,ꢀTG,ꢀ
forꢀinductiveꢀcouplingꢀbetweenꢀC ,ꢀSchottkyꢀandꢀtheꢀtopꢀ
IN
3858fa
ꢁꢇ
LTC3858
applicaTions inForMaTion
SW1
L1
R
SENSE1
V
OUT1
D1
C
R
L1
OUT1
V
IN
R
IN
C
IN
SW2
L2
R
SENSE2
V
OUT2
D2
C
R
L2
OUT2
BOLD LINES INDICATE
HIGH SWITCHING
CURRENT. KEEP LINES
TO A MINIMUM LENGTH.
3858 F11
Figure 11. Branch Current Waveforms
MOSFETꢀcomponentsꢀtoꢀtheꢀsensitiveꢀcurrentꢀandꢀvoltageꢀ Theꢀoutputꢀvoltageꢀunderꢀthisꢀimproperꢀhookupꢀwillꢀstillꢀ
sensingꢀtraces.ꢀInꢀaddition,ꢀinvestigateꢀcommonꢀgroundꢀ beꢀmaintainedꢀbutꢀtheꢀadvantagesꢀofꢀcurrentꢀmodeꢀcontrolꢀ
pathꢀvoltageꢀpickupꢀbetweenꢀtheseꢀcomponentsꢀandꢀtheꢀ willꢀnotꢀbeꢀrealized.ꢀCompensationꢀofꢀtheꢀvoltageꢀloopꢀwillꢀ
SGNDꢀpinꢀofꢀtheꢀIC.
beꢀ muchꢀ moreꢀ sensitiveꢀ toꢀ componentꢀ selection.ꢀ Thisꢀ
behaviorꢀcanꢀbeꢀinvestigatedꢀbyꢀtemporarilyꢀshortingꢀoutꢀ
theꢀcurrentꢀsensingꢀresistor—don’tꢀworry,ꢀtheꢀregulatorꢀ
willꢀstillꢀmaintainꢀcontrolꢀofꢀtheꢀoutputꢀvoltage.
Anꢀembarrassingꢀproblem,ꢀwhichꢀcanꢀbeꢀmissedꢀinꢀanꢀ
otherwiseꢀproperlyꢀworkingꢀswitchingꢀregulator,ꢀresultsꢀ
whenꢀtheꢀcurrentꢀsensingꢀleadsꢀareꢀhookedꢀupꢀbackwards.ꢀ
3858fa
ꢁꢈ
LTC3858
Typical applicaTions
R
B1
INTV
215k
CC
LTC3858
+
100k
C
15pF
SENSE1
F1
PGOOD2
C1
1nF
100k
–
R
A1
68.1k
SENSE1
PGOOD1
BG1
L1
3.3µH
MBOT1
MTOP1
V
FB1
V
3.3V
5A
OUT1
C
ITH1A
150pF
SW1
R
C
C
SENSE1
7mΩ
OUT1
B1
0.47µF
BOOST1
TG1
150µF
R
ITH1
15k
I
TH1
D1
D2
C
ITH1
820pF
C
SS1
0.1µF
V
IN
V
IN
9V TO 38V
C
IN
22µF
SS1
I
INTV
CC
LIM
PHSMD
C
INT
4.7µF
CLKOUT
PLLIN/MODE
SGND
PGND
MTOP2
MBOT2
EXTV
TG2
CC
RUN1
RUN2
FREQ
C
B2
0.47µF
BOOST2
L2
7.2µH
R
SENSE2
10mΩ
C
0.1µF
SS2
V
8.5V
3A
OUT2
SW2
BG2
SS2
C
C
680pF
OUT2
ITH2
R
27k
150µF
ITH2
I
TH2
C
100pF
C2
ITH2A
V
FB2
R
A2
44.2k
–
+
SENSE2
C
1nF
F2
39pF
SENSE2
R
B2
422k
3858 F12
C
, C : SANYO 10TPD150M
OUT1 OUT2
L1: SUMIDA CDEP105-3R2M
L2: SUMIDA CDEP105-7R2M
MTOP1, MTOP2, MBOT1, MBOT2: VISHAY Si7848DP
Efficiency vs Output Current
Start-Up
SW Node Waveforms
100
90
V
80
OUT2
V
OUT
= 8.5V
V
OUT
= 3.3V
2V/DIV
70
SW1
5V/DIV
60
50
V
OUT1
2V/DIV
40
30
20
10
0
SW2
5V/DIV
V
= 12V
IN
Burst Mode OPERATION
0.1 10
OUTPUT CURRENT (A)
3858 F12c
3858 F12d
20ms/DIV
1µs/DIV
0.000010.0001 0.001 0.01
1
3858 F12b
Figure 12. High Efficiency Dual 8.5V/3.3V Step-Down Converter
3858fa
ꢂ0
LTC3858
Typical applicaTions
High Efficiency Dual 2.5V/3.3V Step-Down Converter
R
B1
INTV
143k
CC
LTC3858
+
100k
C
22pF
SENSE1
F1
PGOOD2
C1
1nF
100k
–
R
A1
68.1k
SENSE1
PGOOD1
BG1
L1
2.4µH
MBOT1
MTOP1
V
FB1
V
OUT1
2.5V
5A
C
100pF
ITH1A
SW1
R
C
C
SENSE1
7mΩ
OUT1
B1
0.47µF
BOOST1
TG1
150µF
R
ITH1
22k
I
TH1
D1
D2
C
ITH1
820pF
C
SS1
0.01µF
V
IN
V
IN
4V TO 38V
C
IN
22µF
SS1
I
INTV
CC
LIM
PHSMD
C
INT
4.7µF
CLKOUT
PLLIN/MODE
SGND
PGND
MTOP2
MBOT2
EXTV
TG2
CC
RUN1
RUN2
FREQ
C
B2
0.47µF
BOOST2
L2
3.2µH
R
SENSE2
7mΩ
C
0.01µF
SS2
V
3.3V
5A
OUT2
SW2
BG2
SS2
C
C
820pF
OUT2
ITH2
R
15k
150µF
ITH2
I
TH2
C
150pF
C2
ITH2A
V
FB2
R
A2
68.1k
–
+
SENSE2
C
1nF
F2
15pF
SENSE2
R
B2
215k
3858 F13
C
, C : SANYO 10TPD150M
OUT1 OUT2
L1: SUMIDA CDEP105-2R5
L2: SUMIDA CDEP105-3R2M
MTOP1, MTOP2, MBOT1, MBOT2: VISHAY Si7848DP
3858fa
ꢂꢀ
LTC3858
Typical applicaTions
High Efficiency Dual 12V/5V Step-Down Converter
R
B1
422k
INTV
CC
100k
100k
+
–
C
SENSE1
F1
PGOOD2
C1
1nF
33pF
R
A1
SENSE1
PGOOD1
BG1
30.1k
L1
8.8µH
MBOT1
MTOP1
V
FB1
V
12V
3A
OUT1
C
ITH1A
100pF
SW1
R
C
C
SENSE1
OUT1
B1
BOOST1
TG1
10mΩ
47µF
0.47µF
R
ITH1
33k
I
TH1
D1
D2
LTC3858
C
SS1
0.01µF
C
ITH1
680pF
V
IN
V
IN
12.5V TO 38V
C
IN
SS1
22µF
I
INTV
CC
LIM
C
INT
PHSMD
4.7µF
CLKOUT
PLLIN/MODE
SGND
PGND
MTOP2
MBOT2
EXTV
TG2
CC
RUN1
RUN2
FREQ
R
C
FREQ
B2
BOOST2
60k
0.47µF
L2
4.3µH
R
SENSE2
7mΩ
C
0.01µF
SS2
V
5V
5A
OUT2
SW2
BG2
SS2
C
C
680pF
OUT2
ITH2
R
17k
150µF
ITH2
I
TH2
C
100pF
C2
ITH2A
V
FB2
R
A2
C
: KEMET T525D476M016E035
: SANYO 10TPD150M
OUT1
OUT2
–
+
SENSE2
75k
C
L1: SUMIDA CDEP105-8R8M
L2: SUMIDA CDEP105-4R3M
MTOP1, MTOP2, MBOT1, MBOT2: VISHAY Si7848DP
C
1nF
F2
15pF
SENSE2
R
B2
393k
3858 TA02a
3858fa
ꢂꢁ
LTC3858
Typical applicaTions
High Efficiency Dual 24V/5V Step-Down Converter
R
B1
487k
INTV
CC
100k
100k
+
–
C
SENSE1
SENSE1
F1
PGOOD2
C1
1nF
18pF
R
A1
PGOOD1
BG1
16.9k
L1
22µH
MBOT1
MTOP1
V
FB1
V
24V
1A
OUT1
C
100pF
ITH1A
SW1
R
C
C
SENSE1
OUT1
B1
BOOST1
TG1
25mΩ
22µF
0.47µF
R
46k
ITH1
s2
I
TH1
CERAMIC
C
0.01µF
D1
D2
SS1
LTC3858
C
680pF
ITH1
V
IN
V
SS1
IN
28V TO 38V
C
I
INTV
CC
IN
LIM
C
INT
22µF
PHSMD
4.7µF
CLKOUT
PLLIN/MODE
SGND
PGND
MTOP2
MBOT2
EXTV
TG2
CC
RUN1
RUN2
FREQ
R
C
FREQ
B2
BOOST2
60k
0.47µF
L2
4.3µH
R
SENSE2
7mΩ
C
0.01µF
SS2
V
5V
5A
OUT2
SW2
BG2
SS2
C
C
680pF
OUT2
ITH2
R
17k
150µF
ITH2
I
TH2
C
100pF
C2
ITH2A
V
FB2
R
A2
–
+
SENSE2
75k
C
: SANYO 10TPD150M
OUT2
L1: SUMIDA CDRH105R-220M
L2: SUMIDA CDEP105-4R3M
C
1nF
F2
15pF
SENSE2
MTOP1, MTOP2, MBOT1, MBOT2: VISHAY Si7848DP
R
B2
3858 TA04
392k
3858fa
ꢂꢂ
LTC3858
Typical applicaTions
High Efficiency Dual 1V/1.2V Step-Down Converter
R
B1
28.7k
INTV
CC
100k
100k
+
–
C
SENSE1
SENSE1
F1
PGOOD2
C1
1nF
56pF
R
A1
PGOOD1
BG1
115k
L1
0.47µH
MBOT1
MTOP1
V
FB1
V
1V
8A
OUT1
C
ITH1A
200pF
SW1
C
R
OUT1
C
SENSE1
4mΩ
B1
BOOST1
TG1
220µF
0.47µF
R
ITH1
3.93k
s2
I
TH1
D1
D2
LTC3858
C
1000pF
ITH1
C
SS1
0.01µF
V
IN
V
IN
12V
C
IN
SS1
22µF
I
INTV
CC
LIM
C
INT
PHSMD
4.7µF
CLKOUT
PLLIN/MODE
SGND
PGND
MTOP2
MBOT2
EXTV
TG2
CC
RUN1
RUN2
FREQ
R
C
FREQ
B2
BOOST2
60k
0.47µF
L2
0.47µH
R
SENSE2
4mΩ
C
0.01µF
SS2
V
1.2V
8A
OUT2
SW2
BG2
SS2
C
OUT2
C
1000pF
ITH2
220µF
R
3.93k
ITH2
s2
I
TH2
C
200pF
C2
ITH2A
V
FB2
R
C
, C
: SANYO 2R5TPE220M
A2
OUT1 OUT2
–
+
SENSE2
115k
L1: SUMIDA CDEP105-0R4
L2: SUMIDA CDEP105-0R4
MTOP1, MTOP2: RENESAS RJK0305
MBOT1, MBOT2: RENESAS RJK0328
C
1nF
F2
56pF
SENSE2
R
B2
57.6k
3858 TA03a
3858fa
ꢂꢃ
LTC3858
Typical applicaTions
High Efficiency Dual 1V/1.2V Step-Down Converter with Inductor DCR Current Sensing
R
B1
R
S1
1.18k
28.7k
+
C
SENSE1
SENSE1
F1
INTV
CC
C1
0.1µF
56pF
100k
–
R
A1
PGOOD1
115k
L1
0.47µH
MBOT1
MTOP1
V
BG1
SW1
FB1
V
OUT1
C
ITH1A
200pF
1V
C
OUT1 8A
C
B1
BOOST1
TG1
220µF
0.47µF
R
ITH1
3.93k
s2
I
TH1
D1
D2
LTC3858
C
1000pF
ITH1
C
SS1
0.01µF
V
IN
V
IN
12V
C
IN
SS1
22µF
INTV
CC
C
INT
4.7µF
PGND
PLLIN/MODE
SGND
MTOP2
MBOT2
EXTV
TG2
CC
RUN1
RUN2
FREQ
R
C
FREQ
B2
BOOST2
65k
0.47µF
L2
0.47µH
C
0.01µF
SS2
V
OUT2
1.2V
SW2
BG2
SS2
C
OUT2 8A
C
1000pF
ITH2
220µF
R
3.93k
ITH2
s2
I
TH2
C
220pF
C2
ITH2A
V
FB2
R
A2
–
+
SENSE2
115k
C
, C
: SANYO 2R5TPE220M
OUT1 OUT2
L1, L2: VISHAY IHL P2525CZERR47M06
MTOP1, MTOP2: RENESAS RJK0305
MBOT1, MBOT2: RENESAS RJK0328
C
0.1µF
F2
56pF
SENSE2
R
S2
1.18k
R
B2
57.6k
3858 TA05
3858fa
ꢂꢄ
LTC3858
package DescripTion
UH Package
32-Lead Plastic QFN (5mm × 5mm)
(ReferenceꢀLTCꢀDWGꢀ#ꢀ05-08-1693ꢀRevꢀD)
0.70 p0.05
5.50 p0.05
4.10 p0.05
3.45 p 0.05
3.50 REF
(4 SIDES)
3.45 p 0.05
PACKAGE OUTLINE
0.25 p 0.05
0.50 BSC
RECOMMENDED SOLDER PAD LAYOUT
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
BOTTOM VIEW—EXPOSED PAD
PIN 1 NOTCH R = 0.30 TYP
OR 0.35 s 45o CHAMFER
R = 0.05
TYP
0.00 – 0.05
R = 0.115
TYP
0.75 p 0.05
5.00 p 0.10
(4 SIDES)
31 32
0.40 p 0.10
PIN 1
TOP MARK
(NOTE 6)
1
2
3.45 p 0.10
3.50 REF
(4-SIDES)
3.45 p 0.10
(UH32) QFN 0406 REV D
0.200 REF
0.25 p 0.05
0.50 BSC
NOTE:
1. DRAWING PROPOSED TO BE A JEDEC PACKAGE OUTLINE
M0-220 VARIATION WHHD-(X) (TO BE APPROVED)
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.20mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION
ON THE TOP AND BOTTOM OF PACKAGE
3858fa
ꢂꢅ
LTC3858
revision hisTory
REV
DATE
DESCRIPTION
PAGE NUMBER
A
12/09 ChangeꢀtoꢀAbsoluteꢀMaximumꢀRatings
ChangeꢀtoꢀElectricalꢀCharacteristics
ChangeꢀtoꢀTypicalꢀPerformanceꢀCharacteristics
ChangeꢀtoꢀPinꢀFunctions
2
2,ꢀ3,ꢀ4
6
8,ꢀ9
TextꢀChangesꢀtoꢀOperationꢀSection
TextꢀChangesꢀtoꢀApplicationsꢀInformationꢀSection
ChangeꢀtoꢀTableꢀ2
11,ꢀ12,ꢀ13
21,ꢀ22,ꢀ23,ꢀ24,ꢀ26
23
28
38
ChangeꢀtoꢀFigureꢀ10
ChangesꢀtoꢀRelatedꢀParts
3858fa
InformationꢀfurnishedꢀbyꢀLinearꢀTechnologyꢀCorporationꢀisꢀbelievedꢀtoꢀbeꢀaccurateꢀandꢀreliable.ꢀ
However,ꢀnoꢀresponsibilityꢀisꢀassumedꢀforꢀitsꢀuse.ꢀLinearꢀTechnologyꢀCorporationꢀmakesꢀnoꢀrepresenta-
tionꢀthatꢀtheꢀinterconnectionꢀofꢀitsꢀcircuitsꢀasꢀdescribedꢀhereinꢀwillꢀnotꢀinfringeꢀonꢀexistingꢀpatentꢀrights.
ꢂꢆ
LTC3858
relaTeD parTs
PART NUMBER
DESCRIPTION
COMMENTS
LTC3857/LTC3857-1 LowꢀI ,ꢀDualꢀOutputꢀ2-PhaseꢀSynchronousꢀStep-Downꢀ Phase-LockableꢀFixedꢀOperatingꢀFrequencyꢀ50kHzꢀtoꢀ900kHz,ꢀꢀ
Q
DC/DCꢀControllerꢀwithꢀ99%ꢀDutyꢀCycle
4Vꢀ≤ꢀV ꢀ≤ꢀ38V,ꢀꢀ0.8Vꢀ≤ꢀV ꢀ≤ꢀ24V,ꢀI ꢀ=ꢀ50µA,
IN OUT Q
LTC3868/LTC3868-1 LowꢀI ,ꢀDualꢀOutputꢀ2-PhaseꢀSynchronousꢀStep-Downꢀ Phase-LockableꢀFixedꢀOperatingꢀFrequencyꢀ50kHzꢀtoꢀ900kHz,ꢀ
Q
DC/DCꢀControllerꢀwithꢀ99%ꢀDutyꢀCycle
4Vꢀ≤ꢀV ꢀ≤ꢀ24V,ꢀꢀ0.8Vꢀ≤ꢀV ꢀ≤ꢀ14V,ꢀI ꢀ=ꢀ170µA,
IN OUT Q
LTC3834/LTC3834-1 LowꢀI ,ꢀSynchronousꢀStep-DownꢀDC/DCꢀController
Phase-LockableꢀFixedꢀOperatingꢀFrequencyꢀ140kHzꢀtoꢀ650kHz,ꢀ
4Vꢀ≤ꢀV ꢀ≤ꢀ36V,ꢀꢀ0.8Vꢀ≤ꢀV ꢀ≤ꢀ10V,ꢀI ꢀ=ꢀ30µA,
Q
IN
OUT
Q
LTC3835/LTC3835-1 LowꢀI ,ꢀSynchronousꢀStep-DownꢀDC/DCꢀController
Phase-LockableꢀFixedꢀOperatingꢀFrequencyꢀ140kHzꢀtoꢀ650kHz,ꢀ
4Vꢀ≤ꢀV ꢀ≤ꢀ36V,ꢀ0.8Vꢀ≤ꢀV ꢀ≤ꢀ10V,ꢀI ꢀ=ꢀ80µA,
Q
IN
OUT
Q
LT3845
LT3800
LTC3824
LowꢀI ,ꢀHighꢀVoltageꢀSynchronousꢀStep-Downꢀꢀ
AdjustableꢀFixedꢀOperatingꢀFrequencyꢀ100kHzꢀtoꢀ500kHz,ꢀ
4Vꢀ≤ꢀV ꢀ≤ꢀ60V,ꢀ1.23Vꢀ≤ꢀV ꢀ≤ꢀ36V,ꢀI ꢀ=ꢀ120µA,ꢀTSSOP-16
Q
DC/DCꢀController
IN
OUT
Q
LowꢀI ,ꢀHighꢀVoltageꢀSynchronousꢀStep-Downꢀꢀ
Fixedꢀ200kHzꢀOperatingꢀFrequency,ꢀ4Vꢀ≤ꢀV ꢀ≤ꢀ60V,ꢀ1.23Vꢀ≤ꢀV ꢀ≤ꢀ36V,ꢀ
IN OUT
I ꢀ=ꢀ100µA,ꢀTSSOP-16
Q
Q
DC/DCꢀController
LowꢀI ,ꢀHighꢀVoltageꢀDC/DCꢀController,ꢀ100%ꢀDutyꢀCycle SelectableꢀFixedꢀ200kHzꢀtoꢀ600kHzꢀOperatingꢀFrequency,ꢀ
Q
4Vꢀ≤ꢀV ꢀ≤ꢀ60V,ꢀ0.8Vꢀ≤ꢀV ꢀ≤ꢀV ,ꢀI ꢀ=ꢀ40µA,ꢀMSOP-10E
IN
OUT
IN Q
LTC3850/LTC3850-1ꢀ Dualꢀ2-Phase,ꢀHighꢀEfficiencyꢀSynchronousꢀStep-Downꢀ Phase-LockableꢀFixedꢀOperatingꢀFrequencyꢀ250kHzꢀtoꢀ780kHz,ꢀ
LTC3850-2
DC/DCꢀControllers,ꢀR
ꢀorꢀDCRꢀCurrentꢀSensingꢀandꢀ 4Vꢀ≤ꢀV ꢀ≤ꢀ30V,ꢀ0.8Vꢀ≤ꢀV ꢀ≤ꢀ5.25V
SENSE IN OUT
Tracking
LTC3855
Dual,ꢀMultiphase,ꢀSynchronousꢀDC/DCꢀStep-Downꢀ
ControllerꢀwithꢀDiffampꢀandꢀDCRꢀTemperatureꢀ
Compensation
Phase-LockableꢀFixedꢀFrequencyꢀ250kHzꢀtoꢀ770kHz,ꢀꢀ
4.5Vꢀ≤ꢀV ꢀ≤ꢀ38V,ꢀ0.8Vꢀ≤ꢀV ꢀ≤ꢀ12.5V
IN
OUT
LTC3853
TripleꢀOutput,ꢀMultiphaseꢀSynchronousꢀStep-Downꢀ
Phase-LockableꢀFixedꢀOperatingꢀFrequencyꢀ250kHzꢀtoꢀ750kHz,ꢀ
4Vꢀ≤ꢀV ꢀ≤ꢀ24V,ꢀV ꢀUpꢀtoꢀ13.5V
DC/DCꢀController,ꢀR
Tracking
ꢀorꢀDCRꢀCurrentꢀSensingꢀandꢀ
SENSE
IN
OUT
LTC3854
LTC3775
SmallꢀFootprintꢀWideꢀV ꢀRangeꢀSynchronousꢀStep-Downꢀ Fixedꢀ400kHzꢀOperatingꢀFrequency,ꢀ4.5Vꢀ≤ꢀV ꢀ≤ꢀ38V,ꢀꢀ
IN IN
DC/DCꢀController
0.8Vꢀ≤ꢀV ꢀ≤ꢀ5.25V,ꢀ2mmꢀ×ꢀ3mmꢀQFN-12,ꢀMSOP-12
OUT
HighꢀFrequencyꢀSynchronousꢀVoltageꢀModeꢀStep-Downꢀ FastꢀTransientꢀResponse,ꢀt
ꢀ=ꢀ30ns,ꢀ4Vꢀ≤ꢀV ꢀ≤ꢀ38V,ꢀ
ON(MIN)
IN
DC/DCꢀController
0.6Vꢀ≤ꢀV ꢀ≤ꢀ0.8V ,ꢀMSOP-16E,ꢀ3mmꢀ×ꢀ3mmꢀQFN-16
OUT IN
LTC3851A/ꢀ
LTC3851A-1
NoꢀR ™ꢀWideꢀV ꢀRangeꢀSynchronousꢀStep-Downꢀ Phase-LockableꢀFixedꢀOperatingꢀFrequencyꢀ250kHzꢀtoꢀ750kHz,ꢀꢀ
SENSE
IN
DC/DCꢀController
4Vꢀ≤ꢀV ꢀ≤ꢀ38V,ꢀ0.8Vꢀ≤ꢀV ꢀ≤ꢀ5.25V,ꢀMSOP-16E,ꢀ3mmꢀ×ꢀ3mmꢀQFN-16,ꢀ
IN
OUT
SSOP-16
LTC3878/LTC3879 NoꢀR
ꢀConstantꢀOn-TimeꢀSynchronousꢀStep-Downꢀ VeryꢀFastꢀTransientꢀResponse,ꢀt
ꢀ=ꢀ43ns,ꢀ4Vꢀ≤ꢀV ꢀ≤ꢀ38V,ꢀ
SENSE
ON(MIN) IN
DC/DCꢀController
V
ꢀUpꢀ90%ꢀofꢀV ,ꢀMSOP-16E,ꢀ3mmꢀ×ꢀ3mmꢀQFN-16,ꢀSSOP-16
OUT IN
LTM4600HV
10AꢀDC/DCꢀµModule®ꢀCompleteꢀPowerꢀSupply
HighꢀEfficiency,ꢀCompactꢀSize,ꢀUltraFast™ꢀTransientꢀResponse,ꢀ
4.5Vꢀ≤ꢀV ꢀ≤ꢀ28V,ꢀ0.8Vꢀ≤ꢀV ꢀ≤ꢀ5V,ꢀ15mmꢀ×ꢀ15mmꢀ×ꢀ2.8mm
IN
OUT
LTM4601AHV
12AꢀDC/DCꢀµModuleꢀCompleteꢀPowerꢀSupply
HighꢀEfficiency,ꢀCompactꢀSize,ꢀUltrafastꢀTransientꢀResponse,ꢀ
4.5Vꢀ≤ꢀV ꢀ≤ꢀ28V,ꢀ0.8Vꢀ≤ꢀV ꢀ≤ꢀ5V,ꢀ15mmꢀ×ꢀ15mmꢀ×ꢀ2.8mm
IN
OUT
3858fa
LT 0110 REV A • PRINTED IN USA
Linear Technology Corporation
1630ꢀ McCarthyꢀ Blvd.,ꢀ Milpitas,ꢀ CAꢀ 95035-7417
ꢀ
ꢂꢇ
●
●ꢀ
LINEAR TECHNOLOGY CORPORATION 2009
(408)ꢀ432-1900ꢀ ꢀFAX:ꢀ(408)ꢀ434-0507ꢀ www.linear.com
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