LTC3541-3 [Linear]
High Efficiency Buck + VLDO Regulator; 高效率降压+ VLDO稳压器
| 型号： | LTC3541-3 |
| 厂家： | 
Linear |
| 描述： | High Efficiency Buck + VLDO Regulator |
| 文件： | 总20页 (文件大小：380K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LTC3541-3
High Efficiency
Buck + VLDO Regulator
U
DESCRIPTIO
FEATURES
ꢀ High Efficiency 500mA Buck Plus 300mA VLDO
Theꢀ LTC®3541-3ꢀ combinesꢀ aꢀ synchronousꢀ buckꢀ DC/
DCꢀconverterꢀwithꢀaꢀveryꢀlowꢀdropoutꢀlinearꢀregulatorꢀ
(VLDOTMꢀregulator)ꢀandꢀinternalꢀfeedbackꢀresistorꢀnetworksꢀ
toꢀprovideꢀtwoꢀoutputꢀvoltagesꢀfromꢀaꢀsingleꢀinputꢀvoltageꢀ
withꢀminimumꢀexternalꢀcomponents.ꢀWhenꢀconfiguredꢀ
forꢀdualꢀoutputꢀoperation,ꢀtheꢀLTC3541-3’sꢀautoꢀstart-upꢀ
featureꢀwillꢀbringꢀtheꢀ1.575VꢀVLDO/linearꢀregulatorꢀoutputꢀ
intoꢀregulationꢀinꢀaꢀcontrolledꢀmannerꢀpriorꢀtoꢀenablingꢀtheꢀ
1.8Vꢀbuckꢀoutputꢀwithoutꢀtheꢀneedꢀforꢀexternalꢀpinꢀcontrol.ꢀ
Theꢀ300mAꢀVLDO/linearꢀregulatorꢀoutputꢀwillꢀsourceꢀonlyꢀ
30mAꢀuntilꢀtheꢀbuckꢀoutputꢀachievesꢀregulation.ꢀTheꢀinputꢀ
voltageꢀrangeꢀisꢀideallyꢀsuitedꢀforꢀapplicationsꢀpoweredꢀ
fromꢀaꢀLi-Ionꢀbatteryꢀandꢀ5Vꢀorꢀ3.3Vꢀrails.
■
Regulator
ꢀ
ꢀ
Auto Start-Up Powers VLDO/Linear Regulator
Output Prior to Buck Output
■
ꢀ Independent 500mA High Efficiency Buck
(V : 2.7V to 5.5V)
IN
■
■
■
■
■
■
ꢀ 300mA VLDO Regulator with 30mA Standalone Mode
ꢀ No External Schottky Diodes Required
ꢀ FixedꢀBuck Output Voltage: 1.8V
ꢀ VLDO Input Voltage Range (LV : 1.675V to 5.5V)
IN
ꢀ FixedꢀVLDO Output Voltage: 1.575V
ꢀ SelectableꢀFixedꢀFrequency,ꢀPulse-SkipꢀOperation
ꢀ orꢀBurstꢀMode®ꢀOperation
■
ꢀ Short-CircuitꢀProtected
Theꢀsynchronousꢀbuckꢀconverterꢀprovidesꢀaꢀhighꢀefficiencyꢀ
output,ꢀtypicallyꢀ90%.ꢀItꢀcanꢀprovideꢀupꢀtoꢀ500mAꢀofꢀoutputꢀ
currentꢀwhileꢀswitchingꢀatꢀ2.25MHz,ꢀallowingꢀtheꢀuseꢀofꢀ
smallꢀsurfaceꢀmountꢀinductorsꢀandꢀcapacitors.ꢀAꢀmodeꢀ
selectꢀpinꢀallowsꢀBurstꢀModeꢀoperationꢀtoꢀbeꢀenabledꢀforꢀ
higherꢀefficiencyꢀatꢀlightꢀloadꢀcurrents,ꢀorꢀdisabledꢀforꢀlowerꢀ
noise,ꢀconstantꢀfrequencyꢀoperation.ꢀ
■
ꢀ CurrentꢀModeꢀOperationꢀforꢀExcellentꢀLineꢀandꢀLoadꢀ
TransientꢀResponse
■
ꢀ ShutdownꢀCurrent:ꢀ<3µA
■
ꢀ ConstantꢀFrequencyꢀOperation:ꢀ2.25MHz
■
ꢀ LowꢀDropoutꢀBuckꢀOperation:ꢀ100%ꢀDutyꢀCycle
■
ꢀ Small,ꢀThermallyꢀEnhanced,ꢀ10-Leadꢀ(3mmꢀ×ꢀ3mm)ꢀ
DFNꢀPackage
U
TheꢀVLDOꢀregulatorꢀprovidesꢀaꢀlowꢀnoise,ꢀlowꢀvoltageꢀ
outputꢀcapableꢀofꢀprovidingꢀupꢀtoꢀ300mAꢀofꢀoutputꢀcurrentꢀ
usingꢀonlyꢀaꢀ2.2µFꢀceramicꢀcapacitor.ꢀTheꢀinputꢀsupplyꢀ
voltageꢀofꢀtheꢀVLDOꢀregulatorꢀ(LV )ꢀmayꢀcomeꢀfromꢀtheꢀ
buckꢀregulatorꢀorꢀaꢀseparateꢀsupply.
APPLICATIO S
■
ꢀ DigitalꢀCameras
IN
■
ꢀ CellularꢀPhones
■
ꢀ PCꢀCards
, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology
■
ꢀ WirelessꢀandꢀDSLꢀModems
Corporation. VLDO is a trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
■
ꢀ OtherꢀPortableꢀPowerꢀSystems
Protected by U.S. Patents, including 5481178, 6611131, 6304066, 6498466, 6580258.
U
Buck (Burst) Efficiency vs Load Current
TYPICAL APPLICATIO
100
90
80
70
60
50
40
30
20
10
0
1
V
= 3V
IN
LTC3541-3 Typical Application
EFFICIENCY
V
IN
3V TO 5V
0.1
SW
ENVLDO
MODE
POWER
LOSS
0.01
0.001
0.0001
V
IN
2.2µH
10µF
LTC3541-3
ENBUCK
GND
V
OUT
V
OUT1
1.8V
V
OUT2
1.575V
LV
LV
OUT
PGND
IN
2.2µF
1
10
100
1000
35413 TA01a
35413 TA01b
LOAD CURRENT (mA)
35413fc
ꢀ
ꢀ ENVLDO,ꢀENBUCK,ꢀMODE,ꢀSWꢀ......–0.3VꢀtoꢀV ꢀ+ꢀ0.3V
IN
LTC3541-3
W W W U
U
W
U
ABSOLUTE AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
(Note 1)
TOP VIEW
SupplyꢀVoltages:
ꢀ V ,ꢀLV ꢀ.................................................. –0.3Vꢀtoꢀ6V
IN
IN
V
1
2
3
4
5
10 SW
IN
ꢀ LV ꢀ–ꢀV ꢀ..........................................................<0.3V
IN
IN
ENBUcK
9
8
7
6
ENVLDO
11
V
MODE
GND
PinꢀVoltages:
OUT
Nc
LV
LV
IN
OUT
LinearꢀRegulatorꢀI
ꢀ(100ms)ꢀ(Noteꢀ9)ꢀ......100mA
OUT(MAX)
OperatingꢀAmbientꢀTemperatureꢀRangeꢀ
(Noteꢀ2).................................................... –40°Cꢀtoꢀ85°C
JunctionꢀTemperatureꢀ(Notesꢀ5,ꢀ10)...................... 125°C
StorageꢀTemperatureꢀRange................... –65°Cꢀtoꢀ125°C
DD PAcKAGE
10-LEAD (3mm × 3mm) PLASTIc DFN
ꢀ=ꢀ125°C,ꢀθ ꢀ=ꢀ43°C/W
JA
EXPOSEDꢀPADꢀ(PINꢀ11)ꢀISꢀPGND,ꢀMUSTꢀBEꢀSOLDEREDꢀTOꢀPCB
ꢀ
ꢀ
T
JMAX
ORDERꢀPARTꢀNUMBER
LTC3541EDD-3
DDꢀPARTꢀMARKING
LCHR
Order OptionsꢀꢀꢀTapeꢀandꢀReel:ꢀAddꢀ#TRꢀ
LeadꢀFree:ꢀAddꢀ#PBFꢀꢀꢀLeadꢀFreeꢀTapeꢀandꢀReel:ꢀAddꢀ#TRPBFꢀ
LeadꢀFreeꢀPartꢀMarking:ꢀhttp://www.linear.com/leadfree/
ConsultꢀLTCꢀMarketingꢀforꢀpartsꢀspecifiedꢀwithꢀwiderꢀoperatingꢀtemperatureꢀranges.
ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 3.6V unless otherwise specified (Notes 2, 3).
SYMBOL
PARAMETER
CONDITIONS
MIN
0.8
TYP
MAX
1.25
5.5
UNITS
Aꢀ
I
PeakꢀInductorꢀCurrent
InputꢀVoltageꢀRange
V ꢀ=ꢀ4.2Vꢀ(Noteꢀ8)
IN
0.95
PK
●
●
V
V
(Noteꢀ4)
2.7
V
IN
BuckꢀV ꢀLineꢀRegulationꢀꢀ
V ꢀ=ꢀ2.7Vꢀtoꢀ5.5V,ꢀENBUCKꢀ=ꢀV ,ꢀꢀ
0.04
2.2
2.2
0.8
0.4
%/V
IN(LINEREG)
IN
IN
IN
ENVLDOꢀ=ꢀ0V,ꢀMODEꢀ=ꢀV ꢀ(Noteꢀ6)
IN
VLDOꢀV ꢀLineꢀRegulationꢀꢀ
V ꢀ=ꢀ3Vꢀtoꢀ5.5V,ꢀLV ꢀ=ꢀ1.575V,ꢀENBUCKꢀ=ꢀV ,ꢀ
mV/V
mV/V
mV/V
IN
IN
OUT
IN
(ReferredꢀtoꢀLV
)
ENVLDOꢀ=ꢀV ,ꢀMODEꢀ=ꢀ0V, I
ꢀ=ꢀ100mAꢀ
OUT
IN
ꢀ OUT(VLDO)
LinearꢀRegulatorꢀV ꢀLineꢀ
Regulationꢀ(ReferredꢀtoꢀLV
V ꢀ=ꢀ3Vꢀtoꢀ5.5V,ꢀLV ꢀ=ꢀ1.575V,ꢀENBUCKꢀ=ꢀ0V,ꢀ
IN OUT
IN
)
ENVLDOꢀ=ꢀV ,ꢀI
ꢀ=ꢀ10mA
OUT
IN OUT(LDO)
LV
LV ꢀLineꢀRegulationꢀꢀ
LV ꢀ=ꢀ1.675Vꢀtoꢀ5.5V,ꢀV ꢀ=ꢀ5.5V,ꢀLV ꢀ=ꢀ1.575V,ꢀꢀ
IN IN OUT
IN(LINEREG)
IN
(ReferredꢀtoꢀLV
)
ENBUCKꢀ=ꢀV ,ꢀENVLDOꢀ=ꢀV ,ꢀMODEꢀ=ꢀV ,ꢀꢀ
OUT
IN
IN
IN
I
ꢀ=ꢀ100mA
OUT(VLDO)
VLDO
LV ꢀ–ꢀLV ꢀDropoutꢀVoltage LV ꢀ=ꢀ1.575V,ꢀENBUCKꢀ=ꢀV ,ꢀENVLDOꢀ=ꢀV ,ꢀꢀ
20
50
mV
DO
IN
OUT
OUT
IN
IN
MODEꢀ=ꢀV ,ꢀI
ꢀ=ꢀ50mAꢀ(Noteꢀ9)
IN OUT(VLDO)
V
BuckꢀOutputꢀLoadꢀRegulationꢀ ENBUCKꢀ=ꢀV ,ꢀENVLDOꢀ=ꢀ0V,ꢀMODEꢀ=ꢀV ꢀ(Noteꢀ6)
0.5
%
%
LOADREG
IN
IN
●
●
VLDOꢀOutputꢀLoadꢀRegulationꢀ
I
ꢀ=ꢀ1mAꢀ–ꢀ300mA,ꢀLV ꢀ=ꢀ1.8V,ꢀLV ꢀ=ꢀ1.575V,ꢀ
0.25
0.5
0.5
OUT(VLDO)
IN
OUT
ENBUCKꢀ=ꢀV ,ꢀENVLDOꢀ=ꢀV ,ꢀMODEꢀ=ꢀV
IN
IN
IN
LinearꢀRegulatorꢀOutputꢀLoadꢀ
Regulation
I
ꢀ=ꢀ1mAꢀ–ꢀ30mA,ꢀLV ꢀ=ꢀ1.575V,ꢀꢀ
0.25
%
OUT(LDO)
OUT
ENBUCKꢀ=ꢀ0V,ꢀENVLDOꢀ=ꢀV
IN
V
V
ReferenceꢀRegulationꢀVoltageꢀ ENBUCKꢀ=ꢀV ,ꢀENVLDOꢀ=ꢀ0V,ꢀT ꢀ=ꢀ25°C
1.764
1.760
1.755
1.543
1.540
1.536
1.8
1.8
1.836
1.840
1.845
1.607
1.610
1.614
V
V
V
V
V
V
VOUT
IN
A
(Noteꢀ6)ꢀ
ENBUCKꢀ=ꢀV ,ꢀENVLDOꢀ=ꢀ0V,ꢀ0°Cꢀ≤ꢀT ꢀ≤ꢀ85°C
IN
A
●
●
ENBUCKꢀ=ꢀV ,ꢀENVLDOꢀ=ꢀ0V,ꢀ–40°Cꢀ≤ꢀT ꢀ≤ꢀ85°C
1.8
IN
A
ReferenceꢀRegulationꢀVoltageꢀ ENBUCKꢀ=ꢀ0V,ꢀENVLDOꢀ=ꢀV ,ꢀT ꢀ=ꢀ25°C
1.575
1.575
1.575
LVOUT
IN
A
(Noteꢀ7)
ENBUCKꢀ=ꢀ0V,ꢀENVLDOꢀ=ꢀV ,ꢀ0°Cꢀ≤ꢀT ꢀ≤ꢀ85°C
IN
A
ENBUCKꢀ=ꢀ0V,ꢀENVLDOꢀ=ꢀV ,ꢀ–40°Cꢀ≤ꢀT ꢀ≤ꢀ85°C
IN
A
35413fc
ꢁ
LTC3541-3
ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 3.6V unless otherwise specified (Notes 2, 3).
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
I
Buckꢀ+ꢀVLDOꢀꢀ
LV ꢀ=ꢀ1.8V,ꢀLV ꢀ=ꢀ1.575V,ꢀENBUCKꢀ=ꢀV ,ꢀꢀ
85
µA
S
IN
OUT
IN
BurstꢀModeꢀSleepꢀꢀ
ENVLDOꢀ=ꢀV ,ꢀMODEꢀ=ꢀ0V,ꢀI
ꢀ=ꢀ10µA,ꢀꢀ
IN
OUT(VLDO)
V ꢀQuiescentꢀCurrent
IN
V
ꢀ=ꢀ2.03V
VOUT
Buckꢀ+ꢀVLDOꢀꢀ
LV ꢀ=ꢀ1.8V,ꢀLV ꢀ=ꢀ1.575V,ꢀENBUCKꢀ=ꢀV ,ꢀꢀ
315
300
55
µA
µA
µA
µA
µA
IN
OUT
IN
BurstꢀModeꢀActiveꢀ
ENVLDOꢀ=ꢀV ,ꢀMODEꢀ=ꢀV ,ꢀI
ꢀ=ꢀ10µA,ꢀꢀ
IN
IL OUT(VLDO)
V ꢀQuiescentꢀCurrent
IN
V
ꢀ=ꢀ1.575V
VOUT
Buckꢀ+ꢀVLDOꢀ
LV ꢀ=ꢀ1.8V,ꢀLV ꢀ=ꢀ1.575V,ꢀENBUCKꢀ=ꢀV ,ꢀꢀ
IN
OUT
IN
Pulse-SkipꢀModeꢀActiveꢀ
ENVLDOꢀ=ꢀV ,ꢀMODEꢀ=ꢀV ,ꢀI
V
V
ꢀ=ꢀ10µA,ꢀꢀ
IN
IN OUT(VLDO)
V ꢀQuiescentꢀCurrent
ꢀ=ꢀ1.575V
IN
VOUT
Buckꢀ
ꢀ=ꢀ2.03V,ꢀI
ꢀ=ꢀ0A,ꢀENBUCKꢀ=ꢀV ,ꢀ
VOUT
OUT(BUCK)
IN
BurstꢀModeꢀSleepꢀ
ENVLDOꢀ=ꢀ0V,ꢀMODEꢀ=ꢀ0V
V ꢀQuiescentꢀCurrent
IN
Buckꢀ
V
ꢀ=ꢀ1.575V,ꢀI
ꢀ=ꢀ0A,ꢀENBUCKꢀ=ꢀV ,ꢀ
OUT(BUCK)
300
285
VOUT
IN
BurstꢀModeꢀActiveꢀ
ENVLDOꢀ=ꢀ0V,ꢀMODEꢀ=ꢀ0V
V ꢀQuiscentꢀCurrent
IN
Buckꢀ
V
ꢀ=ꢀ1.575V,ꢀI
ꢀ=ꢀ0A,ꢀENBUCKꢀ=ꢀV ,ꢀ
VOUT
OUT(BUCK)
IN
Pulse-SkipꢀModeꢀActiveꢀ
ENVLDOꢀ=ꢀ0V,ꢀMODEꢀ=ꢀV
IN
V ꢀQuiescentꢀCurrent
IN
LinearꢀRegulatorꢀV ꢀQuiescentꢀ LV ꢀ=ꢀ1.575V,ꢀENBUCKꢀ=ꢀV ,ꢀENVLDOꢀ=ꢀV ,ꢀꢀ
50
2.5
0.1
µA
µA
µA
IN
OUT
IL
IN
Current
I
ꢀ=ꢀ10µA
OUT(VLDO)
V ꢀShutdownꢀQuiescentꢀ
ENBUCKꢀ=ꢀ0V,ꢀENVLDOꢀ=ꢀ0V
IN
Current
LV ꢀShutdownꢀQuiescentꢀ
LV ꢀ=ꢀ3.6V,ꢀENBUCKꢀ=ꢀ0V,ꢀENVLDOꢀ=ꢀ0V
IN
IN
Current
●
f
OscillatorꢀFrequency
1.8
0.9
2.25
0.25
0.35
0.01
2.7
1
MHz
Ω
OSC
R
R
I
R
R
ꢀofꢀP-ChannelꢀMOSFET
ꢀofꢀN-ChannelꢀMOSFET
I
I
ꢀ=ꢀ100mA
PFET
DS(ON)
SW
Ω
ꢀ=ꢀ–100mA
SW
NFET
DS(ON)
SWꢀLeakage
Enableꢀ=ꢀ0V,ꢀV ꢀ=ꢀ0Vꢀorꢀ6V,ꢀV ꢀ=ꢀ6V
SW IN
µA
V
LSW
●
●
●
V
InputꢀPinꢀHighꢀThreshold
InputꢀPinꢀLowꢀThreshold
InputꢀPinꢀCurrent
MODE,ꢀENBUCK,ꢀENVLDO
IH
IL
V
I
I
I
MODE,ꢀENBUCK,ꢀENVLDO
0.3
1
V
,ꢀ
0.01
µA
MODE
ENBUCK
ENVLDO
,ꢀ
Note 6:ꢀTheꢀLTC3541-3ꢀisꢀtestedꢀinꢀaꢀproprietaryꢀtestꢀmodeꢀthatꢀconnectsꢀ
ꢀtoꢀtheꢀoutputꢀofꢀtheꢀerrorꢀamplifier.ꢀForꢀtheꢀreferenceꢀregulationꢀ
andꢀlineꢀregulationꢀtests,ꢀtheꢀoutputꢀofꢀtheꢀerrorꢀamplifierꢀisꢀsetꢀtoꢀtheꢀ
midpoint.ꢀForꢀtheꢀloadꢀregulationꢀtest,ꢀtheꢀoutputꢀofꢀtheꢀerrorꢀamplifierꢀisꢀ
drivenꢀtoꢀminimumꢀandꢀmaximumꢀofꢀtheꢀsignalꢀrange.
Note 1:ꢀStressesꢀbeyondꢀthoseꢀlistedꢀunderꢀAbsoluteꢀMaximumꢀRatingsꢀ
mayꢀcauseꢀpermanentꢀdamageꢀtoꢀtheꢀdevice.ꢀExposureꢀtoꢀanyꢀAbsoluteꢀ
MaximumꢀRatingꢀconditionꢀforꢀextendedꢀperiodsꢀmayꢀaffectꢀdeviceꢀ
reliabilityꢀandꢀlifetime.
V
BUCKFB
Note 2:ꢀTheꢀLTC3541-3ꢀisꢀguaranteedꢀtoꢀmeetꢀperformanceꢀspecificationsꢀ
fromꢀ0°Cꢀtoꢀ85°C.ꢀVLDO/linearꢀregulatorꢀoutputꢀisꢀtestedꢀandꢀspecifiedꢀ
underꢀpulseꢀloadꢀconditionsꢀsuchꢀthatꢀT ꢀ≈ꢀT ,ꢀandꢀareꢀ100%ꢀproductionꢀ
Note 7:ꢀMeasurementꢀmadeꢀinꢀclosedꢀloopꢀlinearꢀregulatorꢀconfigurationꢀ
withꢀLV ꢀ=ꢀ1.575V,ꢀI
ꢀ=ꢀ10µA.
LOAD
OUT
J
A
testedꢀatꢀ25°C.ꢀSpecificationsꢀoverꢀtheꢀ–40°Cꢀtoꢀ85°Cꢀoperatingꢀ
temperatureꢀrangeꢀareꢀassuredꢀbyꢀdesign,ꢀcharacterizationꢀandꢀcorrelationꢀ
withꢀstatisticalꢀprocessꢀcontrols.
Note 8:ꢀMeasurementꢀmadeꢀinꢀaꢀproprietaryꢀtestꢀmodeꢀwithꢀslopeꢀ
compensationꢀdisabled.
Note 9:ꢀMeasurementꢀassuredꢀbyꢀdesign,ꢀcharacterizationꢀandꢀstatisticalꢀ
processꢀcontrol.
Note 10:ꢀThisꢀICꢀincludesꢀovertemperatureꢀprotectionꢀthatꢀisꢀintendedꢀ
toꢀprotectꢀtheꢀdeviceꢀduringꢀmomentaryꢀoverloadꢀconditions.ꢀJunctionꢀ
temperatureꢀwillꢀexceedꢀ125°Cꢀwhenꢀovertemperatureꢀprotectionꢀisꢀactive.ꢀ
Continuousꢀoperationꢀaboveꢀtheꢀspecifiedꢀmaximumꢀoperatingꢀjunctionꢀ
temperatureꢀmayꢀimpairꢀdeviceꢀreliability.
Note 3:ꢀMinimumꢀoperatingꢀLV ꢀvoltageꢀrequiredꢀforꢀVLDOꢀregulationꢀis:ꢀꢀ ꢀ
IN
ꢀ
LV ꢀ≥ꢀLV ꢀ+ꢀV
IN OUT DROPOUT
Note 4:ꢀMinimumꢀoperatingꢀV ꢀvoltageꢀrequiredꢀforꢀVLDOꢀandꢀlinearꢀ
IN
regulatorꢀregulationꢀis:ꢀꢀ
ꢀ
ꢀ
ꢀ
V ꢀ≥ꢀLV ꢀ+ꢀ1.4V
IN
OUT
Note 5:ꢀT ꢀisꢀcalculatedꢀfromꢀtheꢀambientꢀtemperature,ꢀT ,ꢀandꢀpowerꢀ
J
A
dissipation,ꢀP ,ꢀaccordingꢀtoꢀtheꢀfollowingꢀformula:
D
ꢀ
T ꢀ=ꢀT ꢀ+ꢀ(P ꢀ•ꢀ43°C/W)
J A D
35413fc
ꢂ
LTC3541-3
W U
TYPICAL PERFOR A CE CHARACTERISTICS
Efficiency vs Input Voltage for
Buck (Pulse Skip)
Efficiency vs Input Voltage for
Buck (Burst)
Efficiency vs Load Current for
Buck (Pulse Skip)
100
90
80
70
60
50
40
30
20
10
0
100
95
90
85
80
75
70
65
60
55
50
95
90
85
80
75
70
65
60
55
50
V
= 2.7V
IN
I
= 500mA
OUT
V
= 3.6V
IN
I
= 500mA
OUT
V
= 4.2V
IN
I
= 100mA
OUT
I
= 30mA
I
= 100mA
OUT
OUT
I
= 30mA
OUT
4
INPUT VOLTAGE (V)
0.1
1
10
100
1000
2
3
5
6
2
3
4
5
6
LOAD CURRENT (mA)
INPUT VOLTAGE (V)
35413 G03
35413 G01
35413 G02
VLDO Dropout Voltage
vs Load Current
Buck (Burst) Plus VLDO Bias
Current vs VLDO Load Current
Efficiency vs Load Current for
Buck (Burst)
100
90
80
70
60
50
40
30
20
10
0
100
80
250
200
150
100
50
V
= 2.7V
V
I
= 3.6V
IN
IN
V
= 3.6V
= 0
IN
LOAD_BUCK
I
= I + I
– I
BIAS VIN LVIN LOAD
V
= 3V
IN
V
= 4.2V
IN
V
= 3.6V
IN
60
V
= 4.2V
IN
40
20
0
0
1
10
100
0.1
1
10
100
1000
0
100
150
200
250
300
0.1
1000
50
LOAD CURRENT (mA)
LOAD CURRENT (mA)
LOAD CURRENT (mA)
35413 G04
35413 G06
35413 G05
Output (Auto-Start-Up Sequence)
vs Time
Oscillator Frequency
vs Temperature
Oscillator Frequency
vs Supply Voltage
2.50
2.45
2.40
2.35
2.30
2.25
2.20
2.15
2.10
2.05
2.00
2.5
2.4
2.3
2.2
2.1
2.0
V
= 3.6V
V
= 3.6V
IN
IN
V
OUT
1V/DIV
LV
OUT
1V/DIV
V
IN
2V/DIV
35413 G07
I
I
= 200mA
2ms/DIV
VOUT
LVOUT
= 30mA
–50
0
25
50
75 100 125
–25
5
6
3
4
TEMPERATURE (°C)
SUPPLY VOLTAGE (V)
35413 G08
35413 G09
35413fc
ꢃ
LTC3541-3
W U
TYPICAL PERFOR A CE CHARACTERISTICS
VLDO/Linear Regulator vs
Temperature
Buck Reference vs Temperature
RDS(0N) vs Temperature
0.410
0.408
0.406
0.404
0.402
0.400
0.398
0.396
0.394
0.392
0.390
0.820
0.816
0.812
0.808
0.804
0.800
0.796
0.792
0.788
0.784
0.780
0.700
0.600
0.500
0.400
0.300
0.200
0.100
0
V
= 3.6V
V
= 3.6V
IN
IN
SYNCH SWITCH
MAIN SWITCH
V
V
V
= 2.5V
= 3.6V
= 5.5V
IN
IN
IN
–50
0
25
50
75 100 125
–25
–50
0
25
50
75 100 125
–50 –25
25
50
TEMPERATURE (°C)
75
100 125
–25
0
TEMPERATURE (°C)
TEMPERATURE (°C)
35413 G19
35413 G20
35413 G10
Buck (Pulse Skip) Load Step from
1mA to 500mA
Buck (Burst) Load Step from 1mA
to 500mA
Buck (Burst) and VLDO Output
LV
V
V
OUT
OUT
OUT
10mV/DIV
100mV/DIV
100mV/DIV
AC COUPLED
AC COUPLED
AC COUPLED
I
I
L
L
V
OUT
500mA/DIV
500mA/DIV
10mV/DIV
AC COUPLED
I
I
LOAD
LOAD
500mA/DIV
500mA/DIV
35413 G12
35413 G21
35413 G11
V
V
I
= 3.6V
40µs/DIV
V
LV
V
= 3.6V
OUT
2µs/DIV
V
V
I
= 3.6V
40µs/DIV
IN
OUT
IN
IN
OUT
= 1.8V
= 1.5V
= 1.8V
= 1mA TO 500mA
= 1.875V
= 50mA
= 1mA TO 500mA
LOAD
OUT
LOAD
I
LOAD
Burst Mode OPERATION
VLDO Load Step from 100mA to
300mA
VLDO Load Step from 1mA to
300mA
LV
OUT
20mV/DIV
LV
OUT
AC COUPLED
20mV/DIV
AC COUPLED
I
LOAD
250mA/DIV
I
LOAD
250mA/DIV
35413 G13
35413 G14
V
V
I
= 3.6V
400µs/DIV
V
V
I
= 3.6V
400µs/DIV
IN
OUT
IN
OUT
= 1.575V
= 1.575V
= 1mA TO 300mA
= 100mA TO 300mA
LOAD
LOAD
35413fc
ꢄ
LTC3541-3
W U
TYPICAL PERFOR A CE CHARACTERISTICS
Linear Regulator to VLDO
Transient Step, Load = 1mA
Linear Regulator to VLDO
Transient Step, Load = 30mA
LV
LV
OUT
OUT
10mV/DIV
10mV/DIV
AC COUPLED
AC COUPLED
I
LOAD
I
LOAD
25mA/DIV
5mA/DIV
35413 G15
35413 G16
V
V
I
= 3.6V
40µs/DIV
V
V
I
= 3.6V
40µs/DIV
IN
OUT
IN
OUT
= 1.575V
= 1mA
= 1.575V
= 30mA
LOAD
LOAD
VLDO to Linear Regulator
Transient Step, Load = 1mA
VLDO to Linear Regulator
Transient Step, Load = 30mA
LV
LV
OUT
OUT
10mV/DIV
10mV/DIV
AC COUPLED
AC COUPLED
I
I
LOAD
LOAD
5mA/DIV
25mA/DIV
35413 G17
35413 G18
V
V
I
= 3.6V
40µs/DIV
V
V
I
= 3.6V
40µs/DIV
IN
OUT
IN
OUT
= 1.575V
= 1mA
= 1.575V
= 30mA
LOAD
LOAD
35413fc
ꢅ
LTC3541-3
U U
U
PI FU CTIO S
V (Pin 1):ꢀMainꢀSupplyꢀPin.ꢀThisꢀpinꢀmustꢀbeꢀcloselyꢀ
SW (Pin 10):ꢀSwitchꢀNodeꢀPin.ꢀThisꢀpinꢀconnectsꢀtheꢀ
internalꢀmainꢀandꢀsynchronousꢀpowerꢀMOSFETꢀswitchesꢀ
toꢀtheꢀexternalꢀinductorꢀforꢀtheꢀbuckꢀregulator.
IN
decoupledꢀtoꢀGNDꢀwithꢀaꢀ10µFꢀorꢀgreaterꢀcapacitor.
ENBUCK (Pin 2):ꢀBuckꢀEnableꢀPin.ꢀThisꢀpinꢀenablesꢀtheꢀ
buckꢀregulatorꢀwhenꢀdrivenꢀtoꢀaꢀlogicꢀhigh.
Exposed Pad (Pin 11):ꢀGroundꢀPin.ꢀThisꢀpinꢀmustꢀbeꢀ
solderedꢀtoꢀtheꢀPCBꢀtoꢀprovideꢀbothꢀelectricalꢀcontactꢀtoꢀ
groundꢀandꢀgoodꢀthermalꢀcontactꢀtoꢀtheꢀPCB.
V
(Pin3):ꢀBuckꢀRegulatorꢀOutputꢀPin.ꢀThisꢀpinꢀreceivesꢀ
OUT
theꢀbuckꢀregulator’sꢀoutputꢀvoltage.
Note:ꢀTableꢀ1ꢀdetailsꢀtheꢀtruthꢀtableꢀforꢀtheꢀcontrolꢀpinsꢀ
ofꢀtheꢀLTC3541-3.
NC(Pin4):ꢀNotꢀConnected.ꢀThisꢀpinꢀmustꢀnotꢀbeꢀconnectedꢀ
orꢀcapacitivelyꢀloaded.
Table 1. LTC3541-3 Control Truth Table
LV
(Pin 5):ꢀVLDO/LinearꢀRegulatorꢀOutputꢀPin.ꢀThisꢀ
OUT
PIN NAME
OPERATIONAL DESCRIPTION
pinꢀprovidesꢀtheꢀregulatedꢀoutputꢀvoltageꢀfromꢀtheꢀVLDOꢀ
ENBUCK ENVLDO MODE
orꢀlinearꢀregulator.
0
0
0
1
X
X
LTC3541-3ꢀPoweredꢀDown
LV (Pin 6):ꢀVLDO/LinearꢀRegulatorꢀInputꢀSupplyꢀPin.ꢀ
IN
BuckꢀPoweredꢀDown,ꢀVLDOꢀPoweredꢀ
Down,ꢀLinearꢀRegulatorꢀEnabled
ThisꢀpinꢀprovidesꢀtheꢀinputꢀsupplyꢀvoltageꢀforꢀtheꢀVLDOꢀ
powerꢀFET.
1
1
1
1
0
0
1
1
0
1
0
1
BuckꢀEnabled,ꢀVLDOꢀPoweredꢀDown,ꢀ
LinearꢀRegulatorꢀPoweredꢀDown,ꢀꢀꢀ
BurstꢀModeꢀOperation
GND (Pin 7):ꢀAnalogꢀGroundꢀPin.
BuckꢀEnabled,ꢀVLDOꢀPoweredꢀDown,ꢀ
LinearꢀRegulatorꢀPoweredꢀDown,ꢀꢀ
Pulse-SkipꢀMode
MODE (Pin 8):ꢀBuckꢀModeꢀSelectionꢀPin.ꢀThisꢀpinꢀenablesꢀ
buckꢀPulse-Skipꢀoperationꢀwhenꢀdrivenꢀtoꢀaꢀlogicꢀhighꢀ
andꢀenablesꢀbuckꢀBurstꢀModeꢀoperationꢀwhenꢀdrivenꢀtoꢀ
aꢀlogicꢀlow.
BuckꢀEnabled,ꢀVLDOꢀEnabled,ꢀLinearꢀ
RegulatorꢀPoweredꢀDown,ꢀBurstꢀModeꢀ
Operation
ENVLDO (Pin 9):ꢀ VLDO/Linearꢀ Regulatorꢀ Enableꢀ Pin.ꢀ
Whenꢀdrivenꢀtoꢀaꢀlogicꢀhigh,ꢀthisꢀpinꢀenablesꢀtheꢀlinearꢀ
regulatorꢀwhenꢀtheꢀENBUCKꢀpinꢀisꢀdrivenꢀtoꢀaꢀlogicꢀlow,ꢀ
andꢀenablesꢀtheꢀVLDOꢀregulatorꢀwhenꢀtheꢀENBUCKꢀpinꢀisꢀ
drivenꢀtoꢀaꢀlogicꢀhigh.
BuckꢀEnabled,ꢀVLDOꢀEnabled,ꢀLinearꢀ
RegulatorꢀPoweredꢀDown,ꢀPulse-Skipꢀ
Mode
35413fc
ꢆ
LTC3541-3
U
U
W
FU CTIO AL BLOCK DIAGRA
V
I
= 1.8V
= 500mA
OUT(BUCK)
OUT(BUCK)
2.2µH
V
≥ LV
+ 1.4V
OUT
IN(MIN)
10µF
10
SW
V
IN
1
500mA BUCK
SW
V
IN
REF
FB
GND
V
OUT
3
6
PGND
LV
IN
VLDO/LINEAR REG
V
LV
IN
IN
REF
LV
= 1.575V
OUT
+
REF
I
I
= 300mA (LDO)
OUT
OUT
= 30mA (LINEAR REG)
LFB
ENBUCK
ENVLDO
MODE
LV
OUT
–
2
9
8
5
CNTRL
CONTROL
LOGIC
GND
2.2µF
GND
7
PGND
11
35413 F01
Figure 1. LTC3541-3 Functional Block Diagram
35413fc
ꢇ
LTC3541-3
U
OPERATIO
TheꢀLTC3541-3ꢀcontainsꢀaꢀhighꢀefficiencyꢀsynchronousꢀ
buckꢀconverter,ꢀaꢀveryꢀlowꢀdropoutꢀregulatorꢀ(VLDO)ꢀandꢀ
aꢀlinearꢀregulator.ꢀItꢀcanꢀbeꢀusedꢀtoꢀprovideꢀupꢀtoꢀtwoꢀ
outputꢀvoltagesꢀfromꢀaꢀsingleꢀinputꢀvoltageꢀmakingꢀtheꢀ
LTC3541-3ꢀidealꢀforꢀapplicationsꢀwithꢀlimitedꢀboardꢀspace.ꢀ
Theꢀcombinationꢀandꢀconfigurationꢀofꢀtheseꢀmajorꢀblocksꢀ
withinꢀtheꢀLTC3541-3ꢀisꢀdeterminedꢀbyꢀwayꢀofꢀtheꢀcontrolꢀ
pinsꢀENBUCKꢀandꢀENVLDOꢀasꢀdefinedꢀinꢀTableꢀ1.
Buck Regulator Control Loop
TheꢀLTC3541-3ꢀinternalꢀbuckꢀregulatorꢀusesꢀaꢀconstantꢀ
frequency,ꢀcurrentꢀmode,ꢀstep-downꢀarchitecture.ꢀBothꢀtheꢀ
mainꢀ(top,ꢀP-channelꢀMOSFET)ꢀandꢀsynchronousꢀ(bottom,ꢀ
N-channelꢀMOSFET)ꢀswitchesꢀareꢀinternal.ꢀDuringꢀnormalꢀ
operation,ꢀtheꢀinternalꢀmainꢀswitchꢀisꢀturnedꢀonꢀatꢀtheꢀbe-
ginningꢀofꢀeachꢀclockꢀcycleꢀprovidedꢀtheꢀinternalꢀfeedbackꢀ
voltageꢀtoꢀtheꢀbuckꢀisꢀlessꢀthanꢀtheꢀreferenceꢀvoltage.ꢀTheꢀ
currentꢀintoꢀtheꢀinductorꢀprovidedꢀtoꢀtheꢀloadꢀincreasesꢀ
untilꢀtheꢀcurrentꢀlimitꢀisꢀreached.ꢀOnceꢀtheꢀcurrentꢀlimitꢀisꢀ
reachedꢀtheꢀmainꢀswitchꢀturnsꢀoffꢀandꢀtheꢀenergyꢀstoredꢀ
inꢀtheꢀinductorꢀflowsꢀthroughꢀtheꢀbottomꢀsynchronousꢀ
switchꢀintoꢀtheꢀloadꢀuntilꢀtheꢀnextꢀclockꢀcycle.
WithꢀtheꢀENBUCKꢀpinꢀdrivenꢀtoꢀaꢀlogicꢀhighꢀandꢀENVLDOꢀ
drivenꢀtoꢀaꢀlogicꢀlow,ꢀtheꢀLTC3541-3ꢀenablesꢀtheꢀbuckꢀ
converterꢀtoꢀefficientlyꢀreduceꢀtheꢀvoltageꢀprovidedꢀatꢀtheꢀ
V ꢀinputꢀpinꢀtoꢀanꢀoutputꢀvoltageꢀofꢀ1.8Vꢀasꢀdeterminedꢀbyꢀ
IN
anꢀinternalꢀfeedbackꢀresistorꢀnetwork.ꢀTheꢀbuckꢀregulatorꢀ
canꢀbeꢀconfiguredꢀforꢀPulse-SkipꢀorꢀBurstꢀModeꢀopera-
tionꢀbyꢀdrivingꢀtheꢀMODEꢀpinꢀtoꢀaꢀlogicꢀhighꢀorꢀlogicꢀlowꢀ
respectively.ꢀTheꢀbuckꢀregulatorꢀisꢀcapableꢀofꢀprovidingꢀ
aꢀmaximumꢀoutputꢀcurrentꢀofꢀ500mA,ꢀwhichꢀmustꢀbeꢀ
takenꢀintoꢀconsiderationꢀwhenꢀusingꢀtheꢀbuckꢀregulatorꢀ
toꢀprovideꢀtheꢀpowerꢀforꢀbothꢀtheꢀVLDOꢀregulatorꢀandꢀforꢀ
externalꢀloads.ꢀ
Theꢀpeakꢀinductorꢀcurrentꢀisꢀdeterminedꢀbyꢀcomparingꢀtheꢀ
buckꢀfeedbackꢀsignalꢀtoꢀanꢀinternalꢀ0.8Vꢀreference.ꢀWhenꢀ
theꢀloadꢀcurrentꢀincreases,ꢀtheꢀoutputꢀofꢀtheꢀbuckꢀandꢀ
henceꢀtheꢀbuckꢀfeedbackꢀsignalꢀdecrease.ꢀThisꢀdecreaseꢀ
causesꢀtheꢀpeakꢀinductorꢀcurrentꢀtoꢀincreaseꢀuntilꢀtheꢀaver-
ageꢀinductorꢀcurrentꢀmatchesꢀtheꢀloadꢀcurrent.ꢀWhileꢀtheꢀ
mainꢀswitchꢀisꢀoff,ꢀtheꢀsynchronousꢀswitchꢀisꢀturnedꢀonꢀ
untilꢀeitherꢀtheꢀinductorꢀcurrentꢀstartsꢀtoꢀreverseꢀdirectionꢀ
orꢀtheꢀbeginningꢀofꢀaꢀnewꢀclockꢀcycle.
WithꢀtheꢀENBUCKꢀpinꢀdrivenꢀtoꢀaꢀlogicꢀlowꢀandꢀENVLDOꢀ
drivenꢀtoꢀaꢀlogicꢀhigh,ꢀtheꢀLTC3541-3ꢀenablesꢀtheꢀlinearꢀ
regulator,ꢀprovidingꢀaꢀlowꢀnoiseꢀregulatedꢀoutputꢀvoltageꢀofꢀ
WhenꢀtheꢀMODEꢀpinꢀisꢀdrivenꢀtoꢀaꢀlogicꢀlow,ꢀtheꢀLTC3541-3ꢀ
buckꢀregulatorꢀoperatesꢀinꢀBurstꢀModeꢀoperationꢀforꢀhighꢀ
efficiency.ꢀInꢀthisꢀmode,ꢀtheꢀmainꢀswitchꢀoperatesꢀbasedꢀ
uponꢀloadꢀdemand.ꢀInꢀBurstꢀModeꢀoperationꢀtheꢀpeakꢀ
inductorꢀcurrentꢀisꢀsetꢀtoꢀaꢀfixedꢀvalue,ꢀwhereꢀeachꢀburstꢀ
eventꢀcanꢀlastꢀfromꢀaꢀfewꢀclockꢀcyclesꢀatꢀlightꢀloadsꢀtoꢀ
nearlyꢀ continuousꢀ cyclingꢀ atꢀ moderateꢀ loads.ꢀ Betweenꢀ
burstꢀeventsꢀtheꢀmainꢀswitchꢀandꢀanyꢀunneededꢀcircuitryꢀ
areꢀturnedꢀoff,ꢀreducingꢀtheꢀquiescentꢀcurrent.ꢀInꢀthisꢀsleepꢀ
state,ꢀtheꢀloadꢀisꢀbeingꢀsuppliedꢀsolelyꢀfromꢀtheꢀoutputꢀ
capacitor.ꢀAsꢀtheꢀoutputꢀvoltageꢀdroops,ꢀanꢀinternalꢀerrorꢀ
amplifier’sꢀoutputꢀrisesꢀuntilꢀaꢀwakeꢀthresholdꢀisꢀreachedꢀ
causingꢀtheꢀmainꢀswitchꢀtoꢀagainꢀturnꢀon.ꢀThisꢀprocessꢀ
repeatsꢀatꢀaꢀrateꢀthatꢀisꢀdependantꢀuponꢀtheꢀloadꢀcurrentꢀ
demand.
1.575VꢀatꢀtheꢀLV ꢀpinꢀwhileꢀdrawingꢀminimalꢀquiescentꢀ
OUT
currentꢀfromꢀtheꢀV ꢀinputꢀpin.ꢀThisꢀfeatureꢀallowsꢀoutputꢀ
IN
voltageꢀLV ꢀtoꢀbeꢀbroughtꢀintoꢀregulationꢀwithoutꢀtheꢀ
OUT
presenceꢀofꢀtheꢀLV ꢀvoltage.ꢀ
IN
WithꢀtheꢀENBUCKꢀandꢀENVLDOꢀpinsꢀbothꢀdrivenꢀtoꢀaꢀlogicꢀ
high,ꢀtheꢀLTC3541-3ꢀenablesꢀtheꢀhighꢀefficiencyꢀbuckꢀcon-
verterꢀandꢀVLDO,ꢀprovidingꢀdualꢀoutputꢀoperationꢀfromꢀaꢀ
singleꢀinputꢀvoltage.ꢀWhenꢀconfiguredꢀinꢀthisꢀmanner,ꢀtheꢀ
LTC3541-3’sꢀautoꢀstart-upꢀsequencingꢀfeatureꢀwillꢀinitallyꢀ
bringꢀtheꢀVLDO/linearꢀregulatorꢀoutputꢀ(1.575V)ꢀintoꢀregula-
tionꢀinꢀaꢀcontrolledꢀmannerꢀusingꢀtheꢀlinearꢀregulatorꢀpriorꢀ
toꢀenablingꢀtheꢀbuckꢀoutputꢀ(1.8V)ꢀwithoutꢀtheꢀneedꢀforꢀ
externalꢀpinꢀcontrol.ꢀTheꢀLTC3541-3ꢀautomaticallyꢀtransi-
tionsꢀtheꢀVLDO/linearꢀregulatorꢀoutputꢀ(1.575V)ꢀfromꢀtheꢀ
linearꢀregulatorꢀtoꢀtheꢀVLDOꢀregulatorꢀwithinꢀ20msꢀofꢀbuckꢀ
soft-startꢀinitiation.ꢀAꢀdetailedꢀdiscussionꢀofꢀtheꢀtransitionsꢀ
betweenꢀtheꢀVLDOꢀregulatorꢀandꢀlinearꢀregulatorꢀcanꢀbeꢀ
foundꢀinꢀtheꢀVLDO/LinearꢀRegulatorꢀLoopꢀsection.ꢀ
35413fc
ꢈ
LTC3541-3
U
OPERATIO
WhenꢀtheꢀMODEꢀpinꢀisꢀdrivenꢀtoꢀaꢀlogicꢀhighꢀtheꢀLTC3541-3ꢀ
operatesꢀinꢀPulse-Skipꢀmodeꢀforꢀlowꢀoutputꢀvoltageꢀripple.ꢀ
Inꢀthisꢀmode,ꢀtheꢀLTC3541-3ꢀcontinuesꢀtoꢀswitchꢀatꢀaꢀ
constantꢀfrequencyꢀdownꢀtoꢀveryꢀlowꢀcurrents,ꢀwhereꢀitꢀ
willꢀbeginꢀskippingꢀpulsesꢀusedꢀtoꢀcontrolꢀtheꢀmainꢀ(top)ꢀ
switchꢀtoꢀmaintainꢀtheꢀproperꢀaverageꢀinductorꢀcurrent.
TheꢀN-channelꢀMOSFETꢀincorporatedꢀinꢀtheꢀVLDOꢀregulatorꢀ
hasꢀitsꢀdrainꢀconnectedꢀtoꢀtheꢀLV ꢀpinꢀasꢀshownꢀinꢀFigureꢀ
IN
1.ꢀToꢀensureꢀreliableꢀoperation,ꢀtheꢀLV ꢀvoltageꢀmustꢀbeꢀ
IN
stableꢀbeforeꢀtheꢀVLDOꢀregulatorꢀisꢀenabled.ꢀForꢀtheꢀcaseꢀ
whereꢀtheꢀvoltageꢀonꢀLV ꢀisꢀsuppliedꢀbyꢀtheꢀbuckꢀregula-
IN
tor,ꢀtheꢀinternalꢀpowerꢀsupplyꢀsequencingꢀlogicꢀassuresꢀ
voltagesꢀareꢀappliedꢀinꢀtheꢀappropriateꢀmanner.ꢀForꢀtheꢀ
caseꢀwhereꢀtheꢀbuckꢀisꢀenabledꢀbeforeꢀtheꢀVLDOꢀregula-
Ifꢀtheꢀinputꢀsupplyꢀvoltageꢀisꢀdecreasedꢀtoꢀaꢀvalueꢀap-
proachingꢀtheꢀoutputꢀvoltage,ꢀtheꢀdutyꢀcycleꢀofꢀtheꢀbuckꢀ
isꢀincreasedꢀtowardꢀmaximumꢀon-timeꢀandꢀ100%ꢀdutyꢀ
cycle.ꢀTheꢀoutputꢀvoltageꢀwillꢀthenꢀbeꢀdeterminedꢀbyꢀtheꢀ
inputꢀvoltageꢀminusꢀtheꢀvoltageꢀdropꢀacrossꢀtheꢀmainꢀ
switchꢀandꢀtheꢀinductor.
torꢀandꢀanꢀexternalꢀsupplyꢀisꢀusedꢀtoꢀpowerꢀtheꢀLV ꢀpin,ꢀ
IN
theꢀvoltageꢀonꢀLV ꢀpinꢀmustꢀbeꢀstableꢀ1msꢀbeforeꢀtheꢀ
IN
ENVLDOꢀpinꢀisꢀbroughtꢀfromꢀaꢀlowꢀtoꢀaꢀhigh.ꢀFurther,ꢀtheꢀ
externallyꢀsuppliedꢀLV ꢀmustꢀbeꢀreducedꢀinꢀconjunctionꢀ
IN
withꢀV ꢀwheneverꢀV ꢀisꢀpulledꢀlowꢀorꢀremoved.
IN
IN
VLDO/Linear Regulator Loop
Theꢀlinearꢀregulatorꢀisꢀdesignedꢀtoꢀprovideꢀaꢀlowerꢀoutputꢀ
currentꢀ(30mA)ꢀthanꢀthatꢀavailableꢀfromꢀtheꢀVLDOꢀregula-
tor.ꢀTheꢀlinearꢀregulator’sꢀoutput,ꢀpassꢀtransistorꢀhasꢀitsꢀ
InꢀtheꢀLTC3541-3,ꢀtheꢀVLDOꢀandꢀlinearꢀregulatorꢀloopsꢀ
consistꢀofꢀanꢀamplifierꢀandꢀN-channelꢀMOSFETꢀoutputꢀ
stagesꢀthatꢀservoꢀtheꢀoutputꢀtoꢀmaintainꢀaꢀregulatorꢀoutputꢀ
drainꢀtiedꢀtoꢀtheꢀV ꢀrail.ꢀThisꢀallowsꢀtheꢀlinearꢀregulatorꢀ
IN
toꢀbeꢀturnedꢀonꢀpriorꢀto,ꢀandꢀindependentꢀof,ꢀtheꢀbuckꢀ
regulatorꢀwhichꢀordinarilyꢀdrivesꢀtheꢀVLDOꢀregulator.ꢀTheꢀ
linearꢀregulatorꢀisꢀprovidedꢀwithꢀthermalꢀprotectionꢀthatꢀ
isꢀdesignedꢀtoꢀdisableꢀtheꢀlinearꢀregulatorꢀfunctionꢀwhenꢀ
theꢀoutputꢀpassꢀtransistor’sꢀjunctionꢀtemperatureꢀreachesꢀ
approximatelyꢀ160°C.ꢀInꢀadditionꢀtoꢀthermalꢀprotection,ꢀ
short-circuitꢀdetectionꢀisꢀprovidedꢀtoꢀdisableꢀtheꢀlinearꢀ
regulatorꢀfunctionꢀwhenꢀaꢀshort-circuitꢀconditionꢀisꢀsensed.ꢀ
Thisꢀcircuitꢀisꢀdesignedꢀsuchꢀthatꢀanꢀoutputꢀcurrentꢀofꢀ
approximatelyꢀ120mAꢀcanꢀbeꢀprovidedꢀbeforeꢀthisꢀcircuitꢀ
willꢀtrigger.ꢀAsꢀdetailedꢀinꢀtheꢀElectricalꢀCharacteristics,ꢀ
theꢀlinearꢀregulatorꢀwillꢀbeꢀoutꢀofꢀregulationꢀwhenꢀthisꢀ
eventꢀoccurs.ꢀBothꢀtheꢀthermalꢀandꢀshort-circuitꢀfaultsꢀareꢀ
treatedꢀasꢀcatastrophicꢀfaultꢀconditions.ꢀTheꢀLTC3541-3ꢀ
willꢀbeꢀresetꢀuponꢀtheꢀdetectionꢀofꢀeitherꢀevent.ꢀ
voltage,ꢀLV .ꢀLoopꢀconfigurationsꢀenablingꢀtheꢀVLDOꢀorꢀ
OUT
theꢀlinearꢀregulatorꢀareꢀstableꢀwithꢀanꢀoutputꢀcapacitanceꢀ
asꢀlowꢀasꢀ2.2µFꢀandꢀasꢀhighꢀasꢀ100µF.ꢀBothꢀtheꢀVLDOꢀ
regulatorꢀandꢀtheꢀlinearꢀregulatorsꢀareꢀcapableꢀofꢀoperatingꢀ
withꢀanꢀinputꢀvoltage,ꢀV ,ꢀasꢀlowꢀasꢀ3V.ꢀꢀ
IN
TheꢀVLDOꢀregulatorꢀisꢀdesignedꢀtoꢀprovideꢀupꢀtoꢀ300mAꢀ
ofꢀoutputꢀcurrentꢀatꢀaꢀveryꢀlowꢀLV ꢀtoꢀLV ꢀvoltage.ꢀThisꢀ
IN
OUT
allowsꢀaꢀclean,ꢀsecondary,ꢀanalogꢀsupplyꢀvoltageꢀtoꢀbeꢀ
providedꢀwithꢀaꢀminimumꢀdropꢀinꢀefficiency.ꢀTheꢀVLDOꢀ
regulatorꢀisꢀprovidedꢀwithꢀthermalꢀprotectionꢀthatꢀisꢀde-
signedꢀtoꢀdisableꢀtheꢀVLDOꢀfunctionꢀwhenꢀtheꢀoutput,ꢀpassꢀ
transistor’sꢀjunctionꢀtemperatureꢀreachesꢀapproximatelyꢀ
160°C.ꢀ Inꢀ additionꢀ toꢀ thermalꢀ protection,ꢀ short-circuitꢀ
detectionꢀisꢀprovidedꢀtoꢀdisableꢀtheꢀVLDOꢀfunctionꢀwhenꢀ
aꢀshort-circuitꢀconditionꢀisꢀsensed.ꢀThisꢀcircuitꢀisꢀdesignedꢀ
suchꢀthatꢀanꢀoutputꢀcurrentꢀofꢀapproximatelyꢀ1Aꢀcanꢀbeꢀ
providedꢀbeforeꢀthisꢀcircuitꢀwillꢀtrigger.ꢀAsꢀdetailedꢀinꢀtheꢀ
ElectricalꢀCharacteristics,ꢀtheꢀVLDOꢀregulatorꢀwillꢀbeꢀoutꢀ
ofꢀregulationꢀwhenꢀthisꢀeventꢀoccurs.ꢀBothꢀtheꢀthermalꢀ
andꢀ short-circuitꢀ faults,ꢀ whenꢀ detected,ꢀ areꢀ treatedꢀ asꢀ
catastrophicꢀfaultꢀconditions.ꢀTheꢀLTC3541-3ꢀwillꢀbeꢀresetꢀ
uponꢀtheꢀdetectionꢀofꢀeitherꢀevent.
TheꢀN-channelꢀMOSFETꢀincorporatedꢀinꢀtheꢀlinearꢀregulatorꢀ
hasꢀitsꢀdrainꢀconnectedꢀtoꢀtheꢀV ꢀpinꢀasꢀshownꢀinꢀFigureꢀ
IN
1.ꢀTheꢀsizeꢀofꢀtheseꢀMOSFETsꢀandꢀtheirꢀassociatedꢀpowerꢀ
bussingꢀisꢀdesignedꢀtoꢀaccommodateꢀ30mAꢀofꢀDCꢀcurrent.ꢀ
Currentsꢀaboveꢀthisꢀvalueꢀcanꢀbeꢀsupportedꢀforꢀshortꢀperiodsꢀ
asꢀstipulatedꢀinꢀtheꢀAbsoluteꢀMaximumꢀRatings.
35413fc
ꢀ0
LTC3541-3
U
OPERATIO
TransitioningꢀfromꢀlinearꢀregulatorꢀmodeꢀtoꢀVLDOꢀmode,ꢀ
accomplishedꢀbyꢀbringingꢀENBUCKꢀfromꢀaꢀlogicꢀlowꢀtoꢀaꢀ
logicꢀhighꢀwhileꢀENVLDOꢀisꢀaꢀlogicꢀhighꢀorꢀasꢀoccursꢀduringꢀ
theꢀautoꢀstart-upꢀsequence,ꢀisꢀdesignedꢀtoꢀbeꢀasꢀseam-
lessꢀandꢀtransientꢀfreeꢀasꢀpossible.ꢀTheꢀpreciseꢀtransientꢀ
Inꢀaꢀsimilarꢀmanner,ꢀtransitioningꢀfromꢀVLDOꢀmodeꢀtoꢀ
linearꢀregulatorꢀmode,ꢀaccomplishedꢀbyꢀbringingꢀENBUCKꢀ
fromꢀaꢀhighꢀlowꢀtoꢀaꢀlogicꢀlowꢀwhileꢀENVLDOꢀisꢀaꢀlogicꢀ
high,ꢀisꢀdesignedꢀtoꢀbeꢀasꢀseamlessꢀandꢀtransientꢀfreeꢀasꢀ
possible.ꢀAgain,ꢀtheꢀpreciseꢀtransientꢀresponseꢀofꢀLV
ꢀ
OUT
responseꢀofꢀLV ꢀdueꢀtoꢀthisꢀtransitionꢀisꢀaꢀfunctionꢀofꢀ
dueꢀtoꢀthisꢀtransitionꢀisꢀaꢀfunctionꢀofꢀC ꢀandꢀtheꢀloadꢀ
OUT
OUT
C
ꢀandꢀtheꢀloadꢀcurrent.ꢀWaveformsꢀgivenꢀinꢀtheꢀTypicalꢀ
current.ꢀ Waveformsꢀ givenꢀ inꢀ theꢀ Typicalꢀ Performanceꢀ
OUT
PerformanceꢀCharacteristicsꢀsectionꢀshowꢀtypicalꢀtransientꢀ
Characteristicsꢀsectionꢀshowꢀtypicalꢀtransientꢀresponsesꢀ
responsesꢀusingꢀtheꢀminimumꢀC ꢀofꢀ2.2µFꢀandꢀloadꢀ
usingꢀtheꢀminimumꢀC ꢀofꢀ2.2µFꢀandꢀloadꢀcurrentsꢀofꢀ
OUT
OUT
currentsꢀofꢀ1mAꢀandꢀ30mAꢀrespectively.ꢀGenerally,ꢀtheꢀ
1mAꢀandꢀ30mAꢀrespectively.ꢀGenerally,ꢀtheꢀamplitudeꢀofꢀ
amplitudeꢀofꢀanyꢀtransientsꢀpresentꢀwillꢀdecreaseꢀasꢀC
ꢀ
anyꢀtransientsꢀpresentꢀwillꢀdecreaseꢀasꢀC ꢀisꢀincreased.ꢀ
OUT
OUT
isꢀincreased.ꢀToꢀensureꢀreliableꢀoperationꢀandꢀadherenceꢀ
toꢀtheꢀloadꢀregulationꢀlimitsꢀpresentedꢀinꢀtheꢀElectricalꢀ
Charactersticsꢀtable,ꢀtheꢀloadꢀcurrentꢀmustꢀnotꢀexceedꢀ
theꢀlinearꢀregulatorꢀI ꢀlimitꢀofꢀ30mAꢀwithinꢀ20msꢀafterꢀ
ENBUCKꢀhasꢀtransitionedꢀtoꢀaꢀlogicꢀhigh.ꢀTheꢀ300mAꢀI
Toꢀensureꢀreliableꢀoperationꢀandꢀadherenceꢀtoꢀtheꢀloadꢀ
regulationꢀlimitsꢀpresentedꢀinꢀtheꢀElectricalꢀCharactersticsꢀ
table,ꢀtheꢀloadꢀcurrentꢀmustꢀnotꢀexceedꢀtheꢀlinearꢀregulatorꢀ
I
ꢀlimitꢀofꢀ30mAꢀ1msꢀpriorꢀtoꢀENBUCKꢀtransitioningꢀtoꢀ
OUT
OUT
ꢀ
aꢀlogicꢀlowꢀandꢀthereafer.ꢀFurther,ꢀforꢀconfigurationsꢀthatꢀ
doꢀnotꢀuseꢀtheꢀLTC3541-3’sꢀbuckꢀregulatorꢀtoꢀprovideꢀtheꢀ
OUT
limitꢀofꢀVLDOꢀappliesꢀthereafter.ꢀFurther,ꢀforꢀconfigurationsꢀ
thatꢀdoꢀnotꢀuseꢀtheꢀLTC3541-3’sꢀbuckꢀregulatorꢀtoꢀprovideꢀ
VLDOꢀinputꢀvoltageꢀ(LV ),ꢀtheꢀuserꢀmustꢀcontinueꢀtoꢀensureꢀ
IN
theꢀVLDOꢀinputꢀvoltageꢀ(LV ),ꢀtheꢀuserꢀmustꢀensureꢀaꢀ
aꢀstableꢀLV ꢀvoltageꢀnoꢀlessꢀthanꢀ1msꢀafterꢀENBUCKꢀhasꢀ
IN
IN
stableꢀLV ꢀvoltageꢀisꢀpresentꢀnoꢀlessꢀthanꢀ1msꢀpriorꢀtoꢀ
transitionedꢀtoꢀaꢀlogicꢀlow.
IN
ENBUCKꢀtransitioningꢀtoꢀaꢀlogicꢀhigh.
35413fc
ꢀꢀ
LTC3541-3
U U
W U
APPLICATIO S I FOR ATIO
TheꢀbasicꢀLTC3541-3ꢀapplicationꢀcircuitꢀisꢀshownꢀonꢀtheꢀ
firstꢀpageꢀofꢀthisꢀdataꢀsheet.ꢀExternalꢀcomponentꢀselectionꢀ
isꢀdrivenꢀbyꢀtheꢀloadꢀrequirementꢀandꢀrequiresꢀtheꢀselectionꢀ
Table 2. Representative Surface Mount Inductors
PART
NUMBER
VALUE
(µH)
DCR
MAX DC
SIZE
3
(Ω MAX) CURRENT (A) W × L × H (mm )
Sumidaꢀ
CDRH3D23
1.0ꢀ
1.5ꢀ
2.2ꢀ
3.3
0.025ꢀ
0.029ꢀ
0.038ꢀ
0.048
2ꢀ
3.9ꢀ×ꢀ3.9ꢀ×ꢀ2.4
ofꢀL,ꢀfollowedꢀbyꢀC ,ꢀC ,ꢀandꢀfeedbackꢀresistorꢀvaluesꢀ
IN OUT
1.65ꢀ
1.3ꢀ
1.1
forꢀtheꢀbuckꢀandꢀtheꢀselectionꢀofꢀtheꢀoutputꢀcapacitorꢀandꢀ
feedbackꢀvaluesꢀforꢀtheꢀVLDOꢀandꢀlinearꢀregulator.
Sumidaꢀ
2.2ꢀ
3.3
0.116ꢀ
0.174
0.950ꢀ
0.770
3.5ꢀ×ꢀ4.3ꢀ×ꢀ0.8
2.5ꢀ×ꢀ3.2ꢀ×ꢀ2.0
CMD4D06
BUCK REGULATOR
Inductor Selection
Coilcraftꢀ
ME3220
1.0ꢀ
1.5ꢀ
2.2ꢀ
3.3
0.058ꢀ
0.068ꢀ
0.104ꢀ
0.138
2.7ꢀ
2.2ꢀ
1.8ꢀ
1.3
Forꢀmostꢀapplications,ꢀtheꢀappropriateꢀinductorꢀvalueꢀwillꢀbeꢀ
2.2µH.ꢀItsꢀvalueꢀisꢀchosenꢀlargelyꢀbasedꢀonꢀtheꢀdesiredꢀrippleꢀ
currentꢀandꢀburstꢀrippleꢀperformance.ꢀGenerally,ꢀlargeꢀvalueꢀ
inductorsꢀreduceꢀrippleꢀcurrent,ꢀandꢀconversely,ꢀsmallꢀvalueꢀ
Murataꢀ
LQH3C
1.0ꢀ
2.2
0.060ꢀ
0.097
1.00ꢀ
0.79
2.5ꢀ×ꢀ3.2ꢀ×ꢀ2.0
C and C
IN
Selection
OUT
inductorsꢀproduceꢀhigherꢀrippleꢀcurrent.ꢀHigherꢀV ꢀorꢀV
ꢀ
IN
OUT
Inꢀcontinuousꢀmode,ꢀtheꢀsourceꢀcurrentꢀofꢀtheꢀtopꢀMOSFETꢀ
isꢀaꢀsquareꢀwaveꢀofꢀdutyꢀcycleꢀV /V .ꢀToꢀpreventꢀlargeꢀ
voltageꢀtransients,ꢀaꢀlowꢀESRꢀinputꢀcapacitorꢀsizedꢀforꢀtheꢀ
maximumꢀRMSꢀcurrentꢀmustꢀbeꢀused.ꢀTheꢀmaximumꢀRMSꢀ
capacitorꢀcurrentꢀisꢀgivenꢀby:
mayꢀalsoꢀincreaseꢀtheꢀrippleꢀcurrentꢀasꢀshownꢀinꢀEquationꢀ
OUT IN
1.ꢀAꢀreasonableꢀstartingꢀpointꢀforꢀsettingꢀrippleꢀcurrentꢀisꢀ
ΔI ꢀ=ꢀ200mAꢀ(40%ꢀofꢀ500mA).
L
VOUT
VIN
1
ΔIL =
VOUT 1−
(1)
f L
1/2
VOUT V − V
(
)
ꢀ
ꢀ
IN
OUT
cIN required IRMS ≅IOMAX
VIN
TheꢀDCꢀcurrentꢀratingꢀofꢀtheꢀinductorꢀshouldꢀbeꢀatꢀleastꢀ
equalꢀtoꢀtheꢀmaximumꢀloadꢀcurrentꢀplusꢀhalfꢀtheꢀrippleꢀ
currentꢀtoꢀpreventꢀcoreꢀsaturation.ꢀThus,ꢀaꢀ600mAꢀratedꢀ
inductorꢀshouldꢀbeꢀenoughꢀforꢀmostꢀapplicationsꢀ(500mAꢀ
+ꢀ100mA).ꢀForꢀbetterꢀefficiency,ꢀchooseꢀaꢀlowꢀDCꢀresis-
tanceꢀinductor.
ꢀ
Thisꢀ formulaꢀ hasꢀ aꢀ maximumꢀ atꢀ V ꢀ =ꢀ 2V ,ꢀ whereꢀ
IN
OUT
I
ꢀ=ꢀI /2.ꢀThisꢀsimple,ꢀworst-caseꢀconditionꢀisꢀcom-
RMS
OUT
monlyꢀusedꢀforꢀdesign.ꢀNoteꢀthatꢀtheꢀcapacitorꢀmanu-
facturer’sꢀrippleꢀcurrentꢀratingsꢀareꢀoftenꢀbasedꢀonꢀ2000ꢀ
hoursꢀofꢀlife.ꢀThisꢀmakesꢀitꢀadvisableꢀtoꢀfurtherꢀderateꢀtheꢀ
capacitorꢀorꢀchooseꢀaꢀcapacitorꢀratedꢀatꢀaꢀhigherꢀtempera-
tureꢀthanꢀrequired.ꢀAlwaysꢀconsultꢀtheꢀmanufacturerꢀwithꢀ
anyꢀquestionꢀregardingꢀproperꢀcapacitorꢀchoice.
Inductor Core Selection
Differentꢀ coreꢀ materialsꢀ andꢀ shapesꢀ willꢀ changeꢀ theꢀ
size/currentꢀandꢀprice/currentꢀrelationshipꢀofꢀanꢀinduc-
tor.ꢀToroidꢀorꢀshieldedꢀpotꢀcoresꢀinꢀferriteꢀorꢀpermalloyꢀ
materialsꢀareꢀsmallꢀandꢀdon’tꢀradiateꢀmuchꢀenergy,ꢀbutꢀ
generallyꢀcostꢀmoreꢀthanꢀpowderedꢀironꢀcoreꢀinductorsꢀ
withꢀsimilarꢀelectricalꢀcharacteristics.ꢀTheꢀchoiceꢀofꢀwhichꢀ
styleꢀinductorꢀtoꢀuseꢀoftenꢀdependsꢀmoreꢀonꢀtheꢀpriceꢀvsꢀ
sizeꢀrequirementꢀandꢀanyꢀradiatedꢀfield/EMIꢀrequirementsꢀ
ratherꢀthanꢀwhatꢀtheꢀLTC3541-3ꢀrequiresꢀtoꢀoperate.ꢀTableꢀ2ꢀ
showsꢀsomeꢀtypicalꢀsurfaceꢀmountꢀinductorsꢀthatꢀworkꢀ
wellꢀinꢀLTC3541-3ꢀapplications.
TheꢀselectionꢀofꢀC ꢀforꢀtheꢀbuckꢀregulatorꢀisꢀdrivenꢀbyꢀ
OUT
theꢀdesiredꢀbuckꢀloopꢀtransientꢀresponse,ꢀrequiredꢀeffectiveꢀ
seriesꢀresistanceꢀ(ESR)ꢀandꢀburstꢀrippleꢀperformance.
TheꢀLTC3541-3ꢀminimizesꢀtheꢀrequiredꢀnumberꢀofꢀexternalꢀ
componentsꢀbyꢀprovidingꢀinternalꢀloopꢀcompensationꢀforꢀ
theꢀbuckꢀregulatorꢀloop.ꢀLoopꢀstability,ꢀtransientꢀresponseꢀ
andꢀburstꢀrippleꢀperformanceꢀcanꢀbeꢀtailoredꢀbyꢀchoiceꢀ
ofꢀoutputꢀcapacitance.ꢀForꢀmanyꢀapplications,ꢀdesirableꢀ
stability,ꢀtransientꢀresponseꢀandꢀrippleꢀperformanceꢀcanꢀ
35413fc
ꢀꢁ
LTC3541-3
U U
W U
APPLICATIO S I FOR ATIO
beꢀ obtainedꢀ byꢀ choosingꢀ anꢀ outputꢀ capacitorꢀ valueꢀ ofꢀ
10µFꢀtoꢀ22µF.
theꢀlongꢀwiresꢀcanꢀpotentiallyꢀcauseꢀaꢀvoltageꢀspikeꢀatꢀV ,ꢀ
IN
largeꢀenoughꢀtoꢀdamageꢀtheꢀpart.
Typically,ꢀonceꢀtheꢀESRꢀrequirementꢀforꢀC ꢀhasꢀbeenꢀ
Whenꢀchoosingꢀtheꢀinputꢀandꢀoutputꢀceramicꢀcapacitors,ꢀ
chooseꢀtheꢀX5RꢀorꢀX7Rꢀdielectricꢀformulations.ꢀTheseꢀ
dielectricsꢀhaveꢀtheꢀbestꢀtemperatureꢀandꢀvoltageꢀcharac-
teristicsꢀofꢀallꢀtheꢀceramicsꢀforꢀaꢀgivenꢀvalueꢀandꢀsize.
OUT
met,ꢀtheꢀRMSꢀcurrentꢀratingꢀgenerallyꢀfarꢀexceedsꢀtheꢀ
I
ꢀ requirement.ꢀ Theꢀ outputꢀ rippleꢀ ΔV ꢀ isꢀ
RIPPLE(P-P)
OUT
determinedꢀby:
1
Checking Transient Response
ΔVOUT ≅ ΔIL ESR+
8fc
OUT
ꢀ
Theꢀregulatorꢀloopꢀresponseꢀcanꢀbeꢀcheckedꢀbyꢀlookingꢀ
atꢀtheꢀloadꢀtransientꢀresponse.ꢀSwitchingꢀregulatorsꢀtakeꢀ
severalꢀcyclesꢀtoꢀrespondꢀtoꢀaꢀstepꢀinꢀloadꢀcurrent.ꢀWhenꢀ
whereꢀfꢀ=ꢀoperatingꢀfrequency,ꢀC ꢀ=ꢀoutputꢀcapacitanceꢀ
OUT
andꢀΔI ꢀ=ꢀrippleꢀcurrentꢀinꢀtheꢀinductor.ꢀForꢀaꢀfixedꢀoutputꢀ
L
aꢀloadꢀstepꢀoccurs,ꢀV ꢀimmediatelyꢀshiftsꢀbyꢀanꢀamountꢀ
voltage,ꢀtheꢀoutputꢀrippleꢀisꢀhighestꢀatꢀmaximumꢀinputꢀ
OUT
equalꢀtoꢀ(ΔI
ꢀ•ꢀESR),ꢀwhereꢀESRꢀisꢀtheꢀeffectiveꢀseriesꢀ
voltageꢀsinceꢀΔI ꢀincreasesꢀwithꢀinputꢀvoltage.
LOAD
L
resistanceꢀofꢀC .ꢀΔI
ꢀalsoꢀbeginsꢀtoꢀchargeꢀorꢀdis-
OUT
LOAD
Aluminumꢀelectrolyticꢀandꢀdryꢀtantalumꢀcapacitorsꢀareꢀbothꢀ
availableꢀinꢀsurfaceꢀmountꢀconfigurations.ꢀInꢀtheꢀcaseꢀofꢀ
tantalum,ꢀitꢀisꢀcriticalꢀthatꢀtheꢀcapacitorsꢀareꢀsurgeꢀtestedꢀ
forꢀuseꢀinꢀswitchingꢀpowerꢀsupplies.ꢀAnꢀexcellentꢀchoiceꢀisꢀ
theꢀAVXꢀTPSꢀseriesꢀofꢀsurfaceꢀmountꢀtantalum.ꢀTheseꢀareꢀ
speciallyꢀconstructedꢀandꢀtestedꢀforꢀlowꢀESRꢀsoꢀtheyꢀgiveꢀ
theꢀlowestꢀESRꢀforꢀaꢀgivenꢀvolume.ꢀOtherꢀcapacitorꢀtypesꢀ
includeꢀSanyoꢀPOSCAP,ꢀKemetꢀT510ꢀandꢀT495ꢀseries,ꢀandꢀ
Spragueꢀ593Dꢀandꢀ595Dꢀseries.ꢀConsultꢀtheꢀmanufacturerꢀ
forꢀotherꢀspecificꢀrecommendations.
chargeꢀC ,ꢀwhichꢀgeneratesꢀaꢀfeedbackꢀerrorꢀsignal.ꢀTheꢀ
OUT
regulatorꢀloopꢀthenꢀactsꢀtoꢀreturnꢀV ꢀtoꢀitsꢀsteady-stateꢀ
value.ꢀDuringꢀthisꢀrecoveryꢀtimeꢀV ꢀcanꢀbeꢀmonitoredꢀ
OUT
OUT
forꢀovershootꢀorꢀringingꢀthatꢀwouldꢀindicateꢀaꢀstabilityꢀ
problem.ꢀForꢀaꢀdetailedꢀexplanationꢀofꢀswitchingꢀcontrolꢀ
loopꢀtheoryꢀseeꢀApplicationꢀNoteꢀ76.
Aꢀsecond,ꢀmoreꢀsevereꢀtransientꢀisꢀcausedꢀbyꢀswitchingꢀ
inꢀloadsꢀwithꢀlargeꢀ(>1µF)ꢀsupplyꢀbypassꢀcapacitors.ꢀTheꢀ
dischargedꢀbypassꢀcapacitorsꢀareꢀeffectivelyꢀputꢀinꢀparal-
lelꢀwithꢀC ,ꢀcausingꢀaꢀrapidꢀdropꢀinꢀV .ꢀNoꢀregulatorꢀ
OUT
OUT
Using Ceramic Input and Output Capacitors
canꢀdeliverꢀenoughꢀcurrentꢀtoꢀpreventꢀthisꢀproblemꢀifꢀtheꢀ
loadꢀswitchꢀresistanceꢀisꢀlowꢀandꢀitꢀisꢀdrivenꢀquickly.ꢀTheꢀ
onlyꢀsolutionꢀisꢀtoꢀlimitꢀtheꢀriseꢀtimeꢀofꢀtheꢀswitchꢀdriveꢀ
soꢀ thatꢀ theꢀ loadꢀ riseꢀ timeꢀ isꢀ limitedꢀ toꢀ approximatelyꢀ
Highꢀvalue,ꢀlowꢀcostꢀceramicꢀcapacitorsꢀareꢀnowꢀbecomingꢀ
availableꢀinꢀsmallerꢀcaseꢀsizes.ꢀTheirꢀhighꢀrippleꢀcurrent,ꢀ
highꢀvoltageꢀrating,ꢀandꢀlowꢀESRꢀmakeꢀthemꢀidealꢀforꢀ
switchingꢀregulatorꢀapplications.ꢀSinceꢀtheꢀLTC3541-3’sꢀ
controlꢀloopꢀdoesꢀnotꢀdependꢀonꢀtheꢀoutputꢀcapacitor’sꢀESRꢀ
forꢀstableꢀoperation,ꢀceramicꢀcapacitorsꢀcanꢀbeꢀusedꢀfreelyꢀ
toꢀachieveꢀveryꢀlowꢀoutputꢀrippleꢀandꢀsmallꢀcircuitꢀsize.
(25ꢀ•ꢀC
).ꢀThus,ꢀaꢀ10µFꢀcapacitorꢀchargingꢀtoꢀ3.3Vꢀ
LOAD
wouldꢀrequireꢀaꢀ250µsꢀriseꢀtime,ꢀlimitingꢀtheꢀchargingꢀ
currentꢀtoꢀaboutꢀ130mA.
VLDO/LINEAR REGULATOR
However,ꢀcareꢀmustꢀbeꢀtakenꢀwhenꢀceramicꢀcapacitorsꢀ
areꢀusedꢀatꢀtheꢀinputꢀandꢀtheꢀoutput.ꢀWhenꢀaꢀceramicꢀ
capacitorꢀisꢀusedꢀatꢀtheꢀinputꢀandꢀtheꢀpowerꢀisꢀsuppliedꢀ
byꢀaꢀwallꢀadapterꢀthroughꢀlongꢀwires,ꢀaꢀloadꢀstepꢀatꢀtheꢀ
Output Capacitance and Transient Response
TheꢀLTC3541-3ꢀisꢀdesignedꢀtoꢀbeꢀstableꢀwithꢀaꢀwideꢀrangeꢀ
ofꢀceramicꢀoutputꢀcapacitors.ꢀTheꢀESRꢀofꢀtheꢀoutputꢀcapaci-
torꢀaffectsꢀstability,ꢀmostꢀnotablyꢀwithꢀsmallꢀcapacitors.ꢀAꢀ
minimumꢀoutputꢀcapacitorꢀofꢀ2.2µFꢀwithꢀanꢀESRꢀofꢀ0.05Ωꢀ
outputꢀcanꢀinduceꢀringingꢀatꢀtheꢀinput,ꢀV .ꢀAtꢀbest,ꢀthisꢀ
IN
ringingꢀcanꢀcoupleꢀtoꢀtheꢀoutputꢀandꢀbeꢀmistakenꢀasꢀloopꢀ
instability.ꢀAtꢀworst,ꢀaꢀsuddenꢀinrushꢀofꢀcurrentꢀthroughꢀ
35413fc
ꢀꢂ
LTC3541-3
U U
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APPLICATIO S I FOR ATIO
orꢀlessꢀisꢀrecommendedꢀtoꢀensureꢀstability.ꢀTheꢀLTC3541-3ꢀ
VLDOꢀisꢀaꢀmicropowerꢀdeviceꢀandꢀoutputꢀtransientꢀresponseꢀ
willꢀbeꢀaꢀfunctionꢀofꢀoutputꢀcapacitance.ꢀLargerꢀvaluesꢀ
ofꢀoutputꢀcapacitanceꢀdecreaseꢀtheꢀpeakꢀdeviationsꢀandꢀ
provideꢀimprovedꢀtransientꢀresponseꢀforꢀlargerꢀloadꢀcurrentꢀ
changes.ꢀNoteꢀthatꢀbypassꢀcapacitorsꢀusedꢀtoꢀdecoupleꢀ
individualꢀcomponentsꢀpoweredꢀbyꢀtheꢀLTC3541-3ꢀwillꢀ
increaseꢀtheꢀeffectiveꢀoutputꢀcapacitorꢀvalue.ꢀHighꢀESRꢀ
tantalumꢀ andꢀ electrolyticꢀ capacitorsꢀ mayꢀ beꢀ used,ꢀ butꢀ
aꢀlowꢀESRꢀceramicꢀcapacitorꢀmustꢀbeꢀinꢀparallelꢀatꢀtheꢀ
output.ꢀThereꢀisꢀnoꢀminimumꢀESRꢀorꢀmaximumꢀcapacitorꢀ
sizeꢀrequirement.
Extraꢀconsiderationꢀmustꢀbeꢀgivenꢀtoꢀtheꢀuseꢀofꢀceramicꢀ
capacitors.ꢀCeramicꢀcapacitorsꢀareꢀmanufacturedꢀwithꢀaꢀ
varietyꢀofꢀdielectrics,ꢀeachꢀwithꢀdifferentꢀbehaviorꢀacrossꢀ
temperatureꢀ andꢀ appliedꢀ voltage.ꢀ Theꢀ mostꢀ commonꢀ
dielectricsꢀusedꢀareꢀZ5U,ꢀY5V,ꢀX5RꢀandꢀX7R.ꢀTheꢀZ5Uꢀ
andꢀY5Vꢀdielectricsꢀareꢀgoodꢀforꢀprovidingꢀhighꢀcapaci-
tancesꢀinꢀaꢀsmallꢀpackage,ꢀbutꢀexhibitꢀlargeꢀvoltageꢀandꢀ
temperatureꢀcoefficientsꢀasꢀshownꢀinꢀFiguresꢀ6ꢀandꢀ7.ꢀ
Whenꢀusedꢀwithꢀaꢀ2Vꢀregulator,ꢀaꢀ1µFꢀY5Vꢀcapacitorꢀcanꢀ
loseꢀasꢀmuchꢀasꢀ75%ꢀofꢀitsꢀinitialꢀcapacitanceꢀoverꢀtheꢀ
operatingꢀtemperatureꢀrange.ꢀTheꢀX5RꢀandꢀX7Rꢀdielectricsꢀ
resultꢀinꢀmoreꢀstableꢀcharacteristicsꢀandꢀareꢀusuallyꢀmoreꢀ
suitableꢀforꢀuseꢀasꢀtheꢀoutputꢀcapacitor.ꢀTheꢀX7Rꢀtypeꢀhasꢀ
betterꢀstabilityꢀacrossꢀtemperature,ꢀwhileꢀtheꢀX5Rꢀisꢀlessꢀ
expensiveꢀandꢀisꢀavailableꢀinꢀhigherꢀvalues.ꢀInꢀallꢀcases,ꢀ
theꢀoutputꢀcapacitanceꢀshouldꢀneverꢀdropꢀbelowꢀ1µFꢀorꢀ
instabilityꢀorꢀdegradedꢀperformanceꢀmayꢀoccur.
20
BOTH cAPAcITORS ARE 1µF,
10V, 0603 cASE SIZE
0
X5R
–20
–40
EFFICIENCY CONSIDERATIONS
Y5V
Generally,ꢀtheꢀefficiencyꢀofꢀaꢀregulatorꢀisꢀequalꢀtoꢀtheꢀout-
putꢀpowerꢀdividedꢀbyꢀtheꢀinputꢀpowerꢀtimesꢀ100%.ꢀItꢀisꢀ
oftenꢀusefulꢀtoꢀanalyzeꢀindividualꢀlossꢀtermsꢀtoꢀdetermineꢀ
whichꢀtermsꢀareꢀlimitingꢀefficiencyꢀandꢀwhatꢀifꢀanyꢀchangeꢀ
wouldꢀyieldꢀtheꢀgreatestꢀimprovement.ꢀEfficiencyꢀcanꢀbeꢀ
expressedꢀas:
–60
–80
–100
0
8
2
4
6
10
Dc BIAS VOLTAGE (V)
35413 F06
ꢀ Efficiencyꢀ=ꢀ100%ꢀ–ꢀ(L1ꢀ+ꢀL2ꢀ+ꢀL3ꢀ+ꢀ...)
Figure 6. Change in Capacitor vs Bias Voltage
whereꢀL1,ꢀL2,ꢀetc.ꢀareꢀtheꢀindividualꢀlossꢀtermsꢀasꢀaꢀper-
centageꢀofꢀinputꢀpower.
20
0
Althoughꢀallꢀdissipativeꢀelementsꢀinꢀtheꢀcircuitꢀproduceꢀ
losses,ꢀthreeꢀmainꢀsourcesꢀtypicallyꢀaccountꢀforꢀtheꢀmajor-
X5R
–20
ityꢀofꢀtheꢀlossesꢀinꢀtheꢀLTC3541-3ꢀcircuits:ꢀV ꢀquiescentꢀ
Y5V
IN
2
–40
–60
current,ꢀI RꢀlossesꢀandꢀlossꢀacrossꢀVLDOꢀoutputꢀdevice.ꢀ
WhenꢀoperatingꢀwithꢀbothꢀtheꢀbuckꢀandꢀVLDOꢀregulatorꢀ
activeꢀ(ENBUCKꢀandꢀENVLDOꢀequalꢀtoꢀlogicꢀhigh),ꢀV ꢀ
IN
quiescentꢀcurrentꢀlossꢀandꢀlossꢀacrossꢀtheꢀVLDOꢀoutputꢀ
–80
BOTH cAPAcITORS ARE 1µF,
deviceꢀdominateꢀtheꢀefficiencyꢀlossꢀatꢀlowꢀloadꢀcurrents,ꢀ
10V, 0603 cASE SIZE
–100
2
whereasꢀtheꢀI RꢀlossꢀandꢀlossꢀacrossꢀtheꢀVLDOꢀoutputꢀ
–50
0
25
50
75
–25
TEMPERATURE (°c)
deviceꢀdominateꢀtheꢀefficiencyꢀlossꢀatꢀmediumꢀtoꢀhighꢀloadꢀ
currents.ꢀAtꢀlowꢀloadꢀcurrentsꢀwithꢀtheꢀpartꢀoperatingꢀwithꢀ
theꢀlinearꢀregulatorꢀ(ENBUCKꢀequalꢀtoꢀlogicꢀlow,ꢀENVLDOꢀ
35413 F07
Figure 7. Change in Capacitor vs Temperature
35413fc
ꢀꢃ
LTC3541-3
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APPLICATIO S I FOR ATIO
equalꢀtoꢀlogicꢀhigh),ꢀefficiencyꢀisꢀtypicallyꢀdominatedꢀbyꢀ
THERMAL CONSIDERATIONS
theꢀlossꢀacrossꢀtheꢀlinearꢀregulatorꢀoutputꢀdeviceꢀandꢀV ꢀ
IN
Theꢀ LTC3541-3ꢀ requiresꢀ theꢀ packageꢀ backplaneꢀ metalꢀ
(GNDꢀpin)ꢀtoꢀbeꢀwellꢀsolderedꢀtoꢀtheꢀPCꢀboard.ꢀThisꢀgivesꢀ
theꢀ DFNꢀ packageꢀ exceptionalꢀ thermalꢀ properties.ꢀ Theꢀ
powerꢀhandlingꢀcapabilityꢀofꢀtheꢀdeviceꢀwillꢀbeꢀlimitedꢀ
byꢀtheꢀmaximumꢀratedꢀjunctionꢀtemperatureꢀofꢀ125°C.ꢀ
TheꢀLTC3541-3ꢀhasꢀinternalꢀthermalꢀlimitingꢀdesignedꢀtoꢀ
protectꢀtheꢀdeviceꢀduringꢀmomentaryꢀoverloadꢀconditions.ꢀ
Forꢀcontinuousꢀnormalꢀconditions,ꢀtheꢀmaximumꢀjunctionꢀ
temperatureꢀratingꢀofꢀ125°Cꢀmustꢀnotꢀbeꢀexceeded.ꢀItꢀisꢀ
importantꢀtoꢀgiveꢀcarefulꢀconsiderationꢀtoꢀallꢀsourcesꢀofꢀ
thermalꢀresistanceꢀfromꢀjunctionꢀtoꢀambient.ꢀAdditionalꢀ
heatꢀsourcesꢀmountedꢀnearbyꢀmustꢀalsoꢀbeꢀconsidered.ꢀ
Forꢀsurfaceꢀmountꢀdevices,ꢀheatꢀsinkingꢀisꢀaccomplishedꢀ
byꢀusingꢀtheꢀheat-spreadingꢀcapabilitiesꢀofꢀtheꢀPCꢀboardꢀ
andꢀitsꢀcopperꢀtraces.ꢀCopperꢀboardꢀstiffenersꢀandꢀplatedꢀ
throughꢀholesꢀcanꢀalsoꢀbeꢀusedꢀtoꢀspreadꢀtheꢀheatꢀgener-
atedꢀbyꢀpowerꢀdevices.
quiescentꢀcurrent.ꢀInꢀaꢀtypicalꢀefficiencyꢀplot,ꢀtheꢀefficiencyꢀ
curveꢀatꢀveryꢀlowꢀloadꢀcurrentsꢀcanꢀbeꢀmisleadingꢀsinceꢀ
theꢀactualꢀpowerꢀlostꢀisꢀofꢀlittleꢀconsequence.
1.ꢀTheꢀV ꢀquiescentꢀcurrentꢀlossꢀinꢀtheꢀbuckꢀisꢀdueꢀtoꢀtwoꢀ
IN
components:ꢀtheꢀDCꢀbiasꢀcurrentꢀasꢀgivenꢀinꢀtheꢀElectricalꢀ
Characteristicsꢀandꢀtheꢀinternalꢀmainꢀswitchꢀandꢀsynchro-
nousꢀswitchꢀgateꢀchargeꢀcurrents.ꢀTheꢀgateꢀchargeꢀcurrentꢀ
resultsꢀfromꢀswitchingꢀtheꢀgateꢀcapacitanceꢀofꢀtheꢀinternalꢀ
powerꢀswitches.ꢀEachꢀtimeꢀtheꢀgateꢀisꢀswitchedꢀfromꢀhighꢀ
toꢀlowꢀtoꢀhighꢀagain,ꢀaꢀpacketꢀofꢀcharge,ꢀdQ,ꢀmovesꢀfromꢀ
V ꢀtoꢀground.ꢀTheꢀresultingꢀdQ/dtꢀisꢀtheꢀcurrentꢀoutꢀofꢀ
IN
V ꢀthatꢀisꢀtypicallyꢀlargerꢀthanꢀtheꢀDCꢀbiasꢀcurrentꢀandꢀ
IN
proportionalꢀtoꢀfrequency.ꢀBothꢀtheꢀDCꢀbiasꢀandꢀgateꢀchargeꢀ
lossesꢀareꢀproportionalꢀtoꢀV ꢀandꢀthusꢀtheirꢀeffectsꢀwillꢀ
IN
beꢀmoreꢀpronouncedꢀatꢀhigherꢀsupplyꢀvoltages.
2
2.ꢀI Rꢀlossesꢀareꢀcalculatedꢀfromꢀtheꢀresistancesꢀofꢀtheꢀ
internalꢀswitches,ꢀR ,ꢀandꢀexternalꢀinductorꢀR .ꢀInꢀcon-
ToꢀavoidꢀtheꢀLTC3541-3ꢀexceedingꢀtheꢀmaximumꢀjunctionꢀ
temperature,ꢀsomeꢀthermalꢀanalysisꢀisꢀrequired.ꢀTheꢀgoalꢀ
ofꢀtheꢀthermalꢀanalysisꢀisꢀtoꢀdetermineꢀwhetherꢀtheꢀpowerꢀ
dissipatedꢀexceedsꢀtheꢀmaximumꢀjunctionꢀtemperatureꢀofꢀ
theꢀpart.ꢀTheꢀtemperatureꢀriseꢀisꢀgivenꢀby:
SW
L
tinuousꢀmode,ꢀtheꢀaverageꢀoutputꢀcurrentꢀflowingꢀthroughꢀ
inductorꢀLꢀisꢀ“chopped”ꢀbetweenꢀtheꢀmainꢀswitchꢀandꢀtheꢀ
synchronousꢀswitch.ꢀThus,ꢀtheꢀseriesꢀresistanceꢀlookingꢀ
intoꢀtheꢀSWꢀpinꢀisꢀaꢀfunctionꢀofꢀbothꢀtopꢀandꢀbottomꢀ
MOSFETꢀR ꢀandꢀtheꢀdutyꢀcycleꢀ(DC)ꢀasꢀfollows:
DS(ON)
ꢀ T ꢀ=ꢀP •ꢀθ
R
Dꢀ JA
ꢀ R ꢀ=ꢀ(R
)(DC)ꢀ+ꢀ(R )(1ꢀ–ꢀDC)
DS(ON)TOP DS(ON)BOT
SW
whereꢀP ꢀisꢀtheꢀpowerꢀdissipatedꢀbyꢀtheꢀregulatorꢀandꢀθ ꢀ
D
JA
TheꢀR
ꢀforꢀbothꢀtheꢀtopꢀandꢀbottomꢀMOSFETsꢀcanꢀ
isꢀtheꢀthermalꢀresistanceꢀfromꢀtheꢀjunctionꢀofꢀtheꢀdieꢀtoꢀ
DS(ON)
beꢀobtainedꢀfromꢀtheꢀTypicalꢀPerformanceꢀCharacteristicsꢀ
theꢀambientꢀtemperature.
2
curves.ꢀThus,ꢀtoꢀobtainꢀI Rꢀlosses,ꢀsimplyꢀaddꢀR ꢀtoꢀ
SW
Theꢀjunctionꢀtemperature,ꢀT ,ꢀisꢀgivenꢀby:
J
R ꢀandꢀmultiplyꢀtheꢀresultꢀbyꢀtheꢀsquareꢀofꢀtheꢀaverageꢀ
L
ꢀ T ꢀ=ꢀT ꢀ+ꢀT
R
outputꢀcurrent.
J
A
whereꢀT ꢀisꢀtheꢀambientꢀtemperature.
3.ꢀLossesꢀinꢀtheꢀVLDO/linearꢀregulatorꢀareꢀdueꢀtoꢀtheꢀDCꢀbiasꢀ
currentsꢀasꢀgivenꢀinꢀtheꢀElectricalꢀCharacteristicsꢀandꢀtoꢀtheꢀ
A
Asꢀanꢀexample,ꢀconsiderꢀtheꢀLTC3541-3ꢀatꢀanꢀinputꢀvolt-
(V ꢀ–ꢀV )ꢀvoltageꢀdropꢀacrossꢀtheꢀinternalꢀoutputꢀdeviceꢀ
IN
OUT
ageꢀV ꢀofꢀ3V,ꢀanꢀLV ꢀvoltageꢀofꢀ1.8Vꢀprovidedꢀbyꢀtheꢀbuckꢀ
IN
IN
transistor.
regulator,ꢀanꢀLV ꢀvoltageꢀofꢀ1.575V,ꢀaꢀloadꢀcurrentꢀofꢀ
OUT
300mAꢀforꢀtheꢀVLDOꢀregulator,ꢀaꢀloadꢀcurrentꢀofꢀ200mAꢀ
forꢀtheꢀbuckꢀ(totalꢀloadꢀforꢀbuckꢀ=ꢀ500mA),ꢀandꢀanꢀambientꢀ
temperatureꢀofꢀ85°C.ꢀFromꢀtheꢀtypicalꢀperformanceꢀgraphꢀ
Otherꢀ lossesꢀ whenꢀ theꢀ buckꢀ andꢀ VLDOꢀ regulatorꢀ areꢀ
inꢀoperationꢀ(ENBUCKꢀandꢀ ENVLDOꢀequalꢀlogicꢀhigh),ꢀ
includingꢀC ꢀandꢀC ꢀESRꢀdissipativeꢀlossesꢀandꢀinduc-
IN
OUT
ofꢀswitchꢀresistance,ꢀtheꢀR
ꢀofꢀtheꢀP-channelꢀswitchꢀatꢀ
torꢀcoreꢀlosses,ꢀgenerallyꢀaccountꢀforꢀlessꢀthanꢀ2%ꢀtotalꢀ
additionalꢀloss.
DS(ON)
35413fc
ꢀꢄ
LTC3541-3
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APPLICATIO S I FOR ATIO
85°Cꢀisꢀapproximatelyꢀ0.25Ω.TheꢀR
ꢀofꢀtheꢀN-channelꢀ
DS(ON)
DESIGN EXAMPLE
switchꢀisꢀapproximatelyꢀ0.4Ω.Therefore,ꢀpowerꢀdissipatedꢀ
Asꢀaꢀdesignꢀexample,ꢀassumeꢀtheꢀLTC3541-3ꢀisꢀusedꢀinꢀ
aꢀsingleꢀlithium-ionꢀbatteryꢀpoweredꢀcellularꢀphoneꢀap-
byꢀtheꢀpartꢀisꢀapproximately:
2
ꢀ P ꢀ=ꢀ(I
) ꢀ•ꢀR
ꢀ+ꢀ(I
)•ꢀ
plication.ꢀTheꢀV ꢀwillꢀbeꢀoperatingꢀfromꢀaꢀmaximumꢀofꢀ
D
LOADBUCK
SW(ON)
LOADVLDO ꢀ
IN
4.2Vꢀdownꢀtoꢀaboutꢀ3V.ꢀTheꢀloadꢀcurrentꢀrequirementꢀisꢀ
aꢀmaximumꢀofꢀ0.5Aꢀforꢀtheꢀbuckꢀoutputꢀbutꢀmostꢀofꢀtheꢀ
timeꢀitꢀwillꢀbeꢀinꢀstandbyꢀmode,ꢀrequiringꢀonlyꢀ2mA.ꢀEf-
ficiencyꢀatꢀbothꢀlowꢀandꢀhighꢀloadꢀcurrentsꢀisꢀimportant.ꢀ
Theꢀoutputꢀvoltageꢀforꢀtheꢀbuckꢀisꢀ1.8V.ꢀTheꢀrequirementꢀforꢀ
theꢀoutputꢀvoltageꢀofꢀtheꢀVLDOꢀregulatorꢀisꢀ1.575Vꢀwhileꢀ
providingꢀupꢀtoꢀ0.3Aꢀofꢀcurrent.ꢀWithꢀthisꢀinformationꢀweꢀ
canꢀcalculateꢀLꢀusingꢀEquationꢀ2:
ꢀ ꢀ ꢀꢀꢀꢀꢀ(LV ꢀ–ꢀLV )ꢀ=ꢀ145mW
IN
OUT
Forꢀtheꢀ3mmꢀ×ꢀ3mmꢀDFNꢀpackage,ꢀtheꢀθ ꢀisꢀ43°C/W.
JA
Thus,ꢀtheꢀjunctionꢀtemperatureꢀofꢀtheꢀregulatorꢀis:
ꢀ T ꢀ=ꢀ85°Cꢀ+ꢀ(0.145)(43)ꢀ=ꢀ91°C
J
whichꢀisꢀwellꢀbelowꢀtheꢀmaximumꢀjunctionꢀtemperatureꢀ
ofꢀ125°C.
Noteꢀthatꢀatꢀhigherꢀsupplyꢀvoltages,ꢀtheꢀjunctionꢀtempera-
VOUT
VIN
1
f ΔI
L =
VOUT 1−
(2)
tureꢀisꢀlowerꢀdueꢀtoꢀreducedꢀswitchꢀresistanceꢀR
.
DS(ON)
L
ꢀ
ꢀ
SubstitutingꢀV ꢀ=ꢀ1.8V,ꢀV ꢀ=ꢀ3.6Vꢀ(typ),ꢀΔI ꢀ=ꢀ200mAꢀ
PC BOARD LAYOUT CHECKLIST
OUT
IN
L
andꢀfꢀ=ꢀ2.25MHzꢀinꢀEquationꢀ3ꢀgives:
Whenꢀlayingꢀoutꢀtheꢀprintedꢀcircuitꢀboard,ꢀtheꢀfollowingꢀ
checklistꢀshouldꢀbeꢀusedꢀtoꢀensureꢀproperꢀoperationꢀofꢀtheꢀ
LTC3541-3.ꢀCheckꢀtheꢀfollowingꢀinꢀyourꢀlayout:
1.8V
2.25MHz(200mA)
1.8V
3.6V
L =
1−
= 2µH
(3)
ꢀ
ꢀ
1.ꢀTheꢀpowerꢀtraces,ꢀconsistingꢀofꢀtheꢀGNDꢀtrace,ꢀtheꢀSWꢀ
Aꢀ2.2µHꢀinductorꢀworksꢀwellꢀforꢀthisꢀapplication.ꢀForꢀbestꢀ
efficiencyꢀchooseꢀaꢀ600mAꢀorꢀgreaterꢀinductorꢀwithꢀlessꢀ
thanꢀ0.2Ωꢀseriesꢀresistance.
traceꢀandꢀtheꢀV ꢀtraceꢀshouldꢀbeꢀkeptꢀshort,ꢀdirectꢀandꢀ
IN
wide.
2.ꢀDoesꢀtheꢀ(+)ꢀplateꢀofꢀC ꢀconnectꢀtoꢀV ꢀasꢀcloselyꢀasꢀ
IN
IN
C ꢀwillꢀrequireꢀanꢀRMSꢀcurrentꢀratingꢀofꢀatꢀleastꢀ0.25Aꢀ
IN
possible?ꢀThisꢀcapacitorꢀprovidesꢀtheꢀACꢀcurrentꢀtoꢀtheꢀ
=ꢀ I
/2ꢀ atꢀ temperature.ꢀ C ꢀ forꢀ theꢀ buckꢀ isꢀ
LOAD(MAX)
OUT
internalꢀpowerꢀMOSFETs.
chosenꢀtoꢀhaveꢀaꢀvalueꢀofꢀ22µFꢀandꢀanꢀESRꢀofꢀlessꢀthanꢀ
0.25Ω.ꢀInꢀmostꢀcases,ꢀaꢀceramicꢀcapacitorꢀwillꢀsatisfyꢀ
thisꢀrequirement.
3.ꢀKeepꢀtheꢀswitchingꢀnode,ꢀSW,ꢀawayꢀfromꢀtheꢀsensitiveꢀ
LFBꢀnode.
4.ꢀ Keepꢀ theꢀ (–)ꢀ platesꢀ ofꢀ C ꢀ andꢀ C ꢀ asꢀ closeꢀ asꢀ
IN
OUT
C
ꢀforꢀtheꢀVLDOꢀregulatorꢀisꢀchosenꢀasꢀ2.2µF.
OUT
possible.
35413fc
ꢀꢅ
LTC3541-3
U
TYPICAL APPLICATIO S
Dual Output with Minimal External Components Using Auto Start-Up Sequence,
Buck in Burst Mode Operation for High Efficiency Down to Low Load Currents
V
IN
3V TO 4.2V
V
OUT
1V/DIV
SW
ENVLDO
MODE
LV
V
OUT
IN
2.2µH
1V/DIV
LTC3541-3
ENBUCK
GND
V
V
V
IN
OUT1
OUT
V
2V/DIV
1.8V
200mA
OUT2
1.575V
300mA
LV
LV
OUT
PGND
IN
10µF
2.2µF
35413TA02b
I
I
= 200mA
LVOUT
2ms/DIV
VOUT
35413 TA02a
= 30mA
Dual Output with Minimal External Components Using Auto Start-Up Sequence,
Buck in Pulse-Skip Mode for Low Noise Operation
V
IN
3V TO 4.2V
V
OUT
1V/DIV
SW
ENVLDO
MODE
V
IN
LV
OUT
2.2µH
LTC3541-3
ENBUCK GND
1V/DIV
V
V
OUT
OUT1
1.8V
V
IN
V
OUT2
2V/DIV
1.575V
300mA
200mA
LV
LV
OUT
PGND
IN
10µF
2.2µF
35413TA03b
35413 TA03a
I
I
= 200mA
LVOUT
2ms/DIV
VOUT
= 30mA
35413fc
ꢀꢆ
LTC3541-3
U
TYPICAL APPLICATIO S
Dual Output Using Minimal External Components with VOUT2 Controlled by External Logic Signal,
Buck in Burst Mode Operation for High Efficiency Down to Low Load Currents
V
IN
3V TO 4.2V
V
OUT
1V/DIV
SW
ENVLDO
MODE
V
IN
LV
OUT
2.2µH
LTC3541-3
1V/DIV
ENBUCK
GND
V
V
V
OUT1
OUT
IN
1.8V
200mA
V
OUT2
1.575V
300mA
2V/DIV
LV
LV
OUT
PGND
IN
10µF
2.2µF
35413TA04b
I
I
= 200mA
LVOUT
4ms/DIV
35413 TA04a
VOUT
= 300mA
Dual Output Using Minimal External Components with VOUT1 Controlled by External Logic Signal,
Buck in Burst Mode Operation for High Efficiency Down to Low Load Currents
V
IN
3V TO 4.2V
V
OUT
1V/DIV
SW
ENVLDO
MODE
LV
V
OUT
IN
1V/DIV
2.2µH
LTC3541-3
ENBUCK GND
V
IN
V
V
OUT
OUT1
1.8V
2V/DIV
V
OUT2
200mA
LV
LV
PGND
1.575V
300mA
IN
OUT
2.2µF
10µF
35413TA05b
I
I
= 200mA
LVOUT
4ms/DIV
VOUT
35413 TA05a
= 30mA
35413fc
ꢀꢇ
LTC3541-3
U
PACKAGE DESCRIPTIO
DD Package
10-Lead Plastic DFN (3mm × 3mm)
(Referenꢀe LTc DWG # 05-08-1699)
0.675 ±0.05
3.50 ±0.05
2.15 ±0.05 (2 SIDES)
1.65 ±0.05
PAcKAGE
OUTLINE
0.25 ± 0.05
0.50
BSc
2.38 ±0.05
(2 SIDES)
RECOMMENDED SOLDER PAD PITcH AND DIMENSIONS
R = 0.115
TYP
6
0.38 ± 0.10
10
3.00 ±0.10
(4 SIDES)
1.65 ± 0.10
(2 SIDES)
PIN 1
TOP MARK
(SEE NOTE 6)
(DD10) DFN 1103
5
1
0.25 ± 0.05
0.50 BSc
0.75 ±0.05
0.200 REF
2.38 ±0.10
(2 SIDES)
0.00 – 0.05
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING TO BE MADE A JEDEc PAcKAGE OUTLINE M0-229 VARIATION OF (WEED-2).
cHEcK THE LTc WEBSITE DATA SHEET FOR cURRENT STATUS OF VARIATION ASSIGNMENT
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 0.15mm 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
35413fc
Information furnished by Linear Teꢀhnology corporation is believed to be aꢀꢀurate and reliable.
However, no responsibility is assumed for its use. Linear Teꢀhnology corporation makes no represen-
tation that the interꢀonneꢀtion of its ꢀirꢀuits as desꢀribed herein will not infringe on existing patent rights.
ꢀꢈ
LTC3541-3
RELATED PARTS
PART NUMBER
LT®3023ꢀ
DESCRIPTION
COMMENTS
V :ꢀ1.8Vꢀtoꢀ20V,ꢀV
Dual,ꢀ2x100mA,ꢀLowꢀNoiseꢀMicropowerꢀLDOꢀ
ꢀ=ꢀ1.22V,ꢀV ꢀ=ꢀ0.30V,ꢀI ꢀ=ꢀ40µA,ꢀI ꢀ<ꢀ1µA,ꢀꢀ
IN
OUT(MIN)
DO
Q
SD
V
ꢀ=ꢀADJ,ꢀDFN,ꢀMSꢀPackages,ꢀLowꢀNoiseꢀ<ꢀ20µV
,ꢀStableꢀwithꢀ
OUT
RMS(P-P)
1µFꢀCeramicꢀCapacitorsꢀ
LT3024ꢀ
Dual,ꢀ100mA/500mA,ꢀLowꢀNoiseꢀMicropowerꢀLDO
300mA,ꢀMicropowerꢀVLDOꢀLinearꢀRegulator
V :ꢀ1.8Vꢀtoꢀ20V,ꢀV
OUT
1µFꢀCeramicꢀCapacitorsꢀ
ꢀ=ꢀ1.22V,ꢀV ꢀ=ꢀ0.30V,ꢀI ꢀ=ꢀ60µA,ꢀI ꢀ<ꢀ1µA,ꢀꢀ
IN
OUT(MIN)
DO
Q
SD
V
ꢀ=ꢀADJ,ꢀDFN,ꢀTSSOPꢀPackages,ꢀLowꢀNoiseꢀ<ꢀ20µV
,ꢀStableꢀwithꢀ
RMS(P-P)
LTC3025ꢀ
V :ꢀ0.9Vꢀtoꢀ5.5V,ꢀV
ꢀ=ꢀ0.4V,ꢀ2.7Vꢀtoꢀ5.5VꢀBiasꢀVoltageꢀRequired,ꢀꢀ
OUT(MIN)
IN
DO
V
ꢀ=ꢀ45mV,ꢀI ꢀ=ꢀ50µA,ꢀI ꢀ<ꢀ1µA,ꢀV ꢀ=ꢀADJ,ꢀDFNꢀPackages,ꢀStableꢀwithꢀ
Q SD OUT
1µFꢀCeramicꢀCapacitors
LTC3407
LTC3407-2
LTC3445
DualꢀSynchronousꢀ600mAꢀSynchronousꢀStep-Downꢀ 1.5MHzꢀConstantꢀFrequencyꢀCurrentꢀModeꢀOperation,ꢀV ꢀfromꢀ2.5Vꢀtoꢀ
IN
DC/DCꢀRegulator
5.5V,ꢀV ꢀDownꢀtoꢀ0.6V,ꢀDFN,ꢀMSꢀPackages
OUT
DualꢀSynchronousꢀ800mAꢀSynchronousꢀStep-Downꢀ 2.25MHzꢀConstantꢀFrequencyꢀCurrentꢀModeꢀOperation,ꢀV ꢀfromꢀ2.5Vꢀtoꢀ
IN
DC/DCꢀRegulator,ꢀ2.25MHz
5.5V,ꢀV ꢀDownꢀtoꢀ0.6V,ꢀDFN,ꢀMSꢀPackages
OUT
2
2
I CꢀControllableꢀBuckꢀRegulatorꢀwithꢀTwoꢀLDOsꢀandꢀ 600mA,ꢀ1.5MHzꢀCurrentꢀModeꢀBuckꢀRegulator,ꢀI CꢀProgrammableꢀ
BackupꢀBatteryꢀInput
V
ꢀfromꢀ0.85Vꢀtoꢀ1.55V,ꢀtwoꢀ50mAꢀLDOs,ꢀBackupꢀBatteryꢀInputꢀwithꢀ
OUT
PowerPathꢀControl,ꢀQFNꢀPackageꢀ
LTC3446
LTC3448
LTC3541
TripleꢀOutputꢀStep-DownꢀConverterꢀ1AꢀOutputꢀBuck,ꢀ V :ꢀ2.7Vꢀtoꢀ5.5V,ꢀV ꢀBuckꢀ=ꢀ0.8V,ꢀV
ꢀVDLOꢀ=ꢀ0.4V
,ꢀ
IN
OUT(MIN)
OUT(MIN)
OUT(MIN)
TwoꢀEachꢀ300mAꢀVDLOs
14-PinꢀDFNꢀPackage
V :ꢀ2.7Vꢀtoꢀ5.5V,ꢀV ꢀ=ꢀ0.6V,ꢀSwitchesꢀtoꢀLDOꢀModeꢀatꢀ≤3A,ꢀꢀ
OUT(MIN)
600mAꢀ(I ),ꢀHighꢀEfficiency,ꢀ1.5MHz/2.25MHzꢀ
OUT
IN
SynchronousꢀStep-DownꢀRegulatorꢀwithꢀLDOꢀMode
DD8,ꢀMS8/EꢀPackages
HighꢀEfficiencyꢀBuckꢀ+ꢀVLDOꢀRegulator
V :ꢀ2.7Vꢀtoꢀ5.5V,ꢀV
ꢀBuckꢀ=ꢀ0.8V,ꢀV
ꢀVLDOꢀ=ꢀ0.4V,ꢀꢀ
IN
OUT(MIN)
OUT(MIN)
3mmꢀ×ꢀ3mmꢀ10-PinꢀDFNꢀPackage
LTC3548/LTC3548-1ꢀ Dualꢀ800mA/400mAꢀI ,ꢀ2.25MHz,ꢀSynchronousꢀꢀ
95%ꢀEfficiency,ꢀV :ꢀ2.5Vꢀtoꢀ5.5V,ꢀV
ꢀ=ꢀ0.6V,ꢀI ꢀ=ꢀ40µA,ꢀI ꢀ<ꢀ1µA,ꢀ
OUT(MIN) Q SD
OUT
IN
LTC3548-2
Step-DownꢀDC/DCꢀConverter
DFNꢀandꢀ10-PinꢀMSꢀPackages
LTC3700
Step-DownꢀDC/DCꢀControllerꢀwithꢀLDOꢀRegulator
V ꢀfromꢀ2.65Vꢀtoꢀ9.8V,ꢀConstantꢀFrequencyꢀ550kHzꢀOperation
IN
PowerPathꢀisꢀaꢀtrademarkꢀofꢀLinearꢀTechnologyꢀCorporation.ꢀ
35413fc
LT 0507 REV C • PRINTED IN USA
LinearTechnology Corporation
1630 Mꢀcarthy Blvd., Milpitas, cA 95035-7417
ꢁ0
●
ꢀ●ꢀ
LINEAR TECHNOLOGY CORPORATION 2006
(408)432-1900 FAX: (408) 434-0507 www.linear.ꢀom
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