LTC3868-1
Low I , Dual
Q
2-Phase Synchronous
Step-Down Controller
FeaTures
DescripTion
TheꢀLTC®3868-1ꢀisꢀaꢀhighꢀperformanceꢀdualꢀstep-downꢀ
switchingꢀregulatorꢀcontrollerꢀthatꢀdrivesꢀallꢀN-channelꢀ
synchronousꢀpowerꢀMOSFETꢀstages.ꢀAꢀconstantꢀfrequencyꢀ
currentꢀmodeꢀarchitectureꢀallowsꢀaꢀphase-lockableꢀfre-
quencyꢀofꢀupꢀtoꢀ850kHz.ꢀPowerꢀlossꢀandꢀnoiseꢀdueꢀtoꢀtheꢀ
inputꢀcapacitorꢀESRꢀareꢀminimizedꢀbyꢀoperatingꢀtheꢀtwoꢀ
controllerꢀoutputsꢀoutꢀofꢀphase.
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ꢀ Low Operating I : 170µA (One Channel On)
Q
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ꢀ Wide Output Voltage Range: 0.8V ≤ V
≤ 14V
OUT
ꢀ Wide V Range: 4V to 24V
IN
ꢀ R
or DCR Current Sensing
SENSE
ꢀ Out-of-PhaseꢀControllersꢀReduceꢀRequiredꢀInputꢀ
CapacitanceꢀandꢀPowerꢀSupplyꢀInducedꢀNoise
®
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ꢀ OPTI-LOOP ꢀCompensationꢀMinimizesꢀC
OUT
ꢀ Phase-LockableꢀFrequencyꢀ(75kHzꢀtoꢀ850kHz)
ꢀ ProgrammableꢀFixedꢀFrequencyꢀ(50kHzꢀtoꢀ900kHz)
ꢀ SelectableꢀContinuous,ꢀPulse-Skippingꢀorꢀ
ꢀBurstꢀMode®ꢀOperationꢀatꢀLightꢀLoads
Theꢀ170μAꢀno-loadꢀquiescentꢀcurrentꢀextendsꢀoperatingꢀ
lifeꢀinꢀbatteryꢀpoweredꢀsystems.ꢀOPTI-LOOPꢀcompensa-
tionꢀallowsꢀtheꢀtransientꢀresponseꢀtoꢀbeꢀoptimizedꢀoverꢀ
aꢀwideꢀrangeꢀofꢀoutputꢀcapacitanceꢀandꢀESRꢀvalues.ꢀTheꢀ
LTC3868-1ꢀfeaturesꢀaꢀprecisionꢀ0.8Vꢀreferenceꢀandꢀaꢀpowerꢀ
goodꢀoutputꢀindicator.ꢀAꢀwideꢀ4Vꢀtoꢀ24Vꢀinputꢀsupplyꢀrangeꢀ
encompassesꢀaꢀwideꢀrangeꢀofꢀintermediateꢀbusꢀvoltagesꢀ
andꢀbatteryꢀchemistries.
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ꢀ VeryꢀLowꢀDropoutꢀOperation:ꢀ99%ꢀDutyꢀCycle
ꢀ AdjustableꢀOutputꢀVoltageꢀSoft-Start
ꢀ PowerꢀGoodꢀOutputꢀVoltageꢀMonitor
ꢀ OutputꢀOvervoltageꢀProtection
ꢀ OutputꢀLatchoffꢀProtectionꢀDuringꢀShortꢀCircuit
Independentꢀsoft-startꢀpinsꢀforꢀeachꢀcontrollerꢀrampꢀtheꢀ
outputꢀvoltagesꢀduringꢀstart-up.ꢀCurrentꢀfoldbackꢀlimitsꢀ
MOSFETꢀheatꢀdissipationꢀduringꢀshort-circuitꢀconditions.ꢀ
Theꢀoutputꢀshort-circuitꢀlatchoffꢀfeatureꢀfurtherꢀprotectsꢀ
theꢀcircuitꢀinꢀshort-circuitꢀconditions.
ꢀ LowꢀShutdownꢀI :ꢀ8µA
Q
ꢀ InternalꢀLDOꢀPowersꢀGateꢀDriveꢀfromꢀV ꢀorꢀEXTV
IN
CC
ꢀ NoꢀCurrentꢀFoldbackꢀDuringꢀStart-Up
ꢀ Smallꢀ4mmꢀ×ꢀ5mmꢀQFNꢀandꢀNarrowꢀSSOPꢀPackages
Forꢀaꢀleadlessꢀ32-pinꢀQFNꢀpackageꢀwithꢀtheꢀadditionalꢀfea-
turesꢀofꢀadjustableꢀcurrentꢀlimit,ꢀclockꢀout,ꢀphaseꢀmodula-
tionꢀandꢀtwoꢀPGOODꢀoutputs,ꢀseeꢀtheꢀLTC3868ꢀdataꢀsheet.ꢀ
L,ꢀLT,ꢀLTC,ꢀLTM,ꢀBurstꢀMode,ꢀOPTI-LOOP,ꢀµModule,ꢀLinearꢀTechnologyꢀandꢀtheꢀLinearꢀlogoꢀ
applicaTions
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ꢀ NotebookꢀandꢀPalmtopꢀComputers
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ꢀ PortableꢀInstruments
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ꢀ BatteryꢀOperatedꢀDigitalꢀDevices
areꢀregisteredꢀtrademarksꢀandꢀNoꢀR
ꢀandꢀUltraFastꢀareꢀtrademarksꢀofꢀLinearꢀTechnologyꢀ
SENSE
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 24V
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
70
EFFICIENCY
BG1
BG2
60
50
LTC3868-1
PGND
POWER LOSS
= 12V
+
+
40
30
20
10
0
SENSE1
SENSE1
SENSE2
0.01Ω
193k
0.007Ω
–
1
–
V
8.5V
3.5A
SENSE2
OUT2
V
V
V
OUT1
3.3V
5A
IN
OUT
V
V
= 3.3V
FB1
FB2
I
TH2
62.5k
FIGURE 12 CIRCUIT
0.1 10
OUTPUT CURRENT (A)
I
TH1
SS1
0.1
150µF
680pF
15k
680pF
15k
150µF
SGND
SS2
0.0001 0.001
0.01
1
20k
20k
0.1µF
0.1µF
38681 TA01b
38681 TA01
38681fb
ꢀ
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