LTC3541-2 [Linear]
High Efficiency Buck + VLDO Regulator; 高效率降压+ VLDO稳压器
| 型号： | LTC3541-2 |
| 厂家： | 
Linear |
| 描述： | High Efficiency Buck + VLDO Regulator |
| 文件： | 总20页 (文件大小：337K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LTC3541-2
High Efficiency
Buck + VLDO Regulator
U
DESCRIPTIO
FEATURES
ꢀ High Efficiency, 500mA Buck Plus 300mA VLDO
TheꢀLTC®3541-2ꢀcombinesꢀaꢀsynchronousꢀbuckꢀDC/
DCꢀconverterꢀwithꢀaꢀveryꢀlowꢀdropoutꢀlinearꢀregulatorꢀ
(VLDOTMregulator)ꢀandꢀinternalꢀfeedbackꢀresistorꢀnetworksꢀ
toꢀprovideꢀtwoꢀoutputꢀvoltagesꢀfromꢀaꢀsingleꢀinputꢀvolt-
ageꢀwithꢀminimalꢀexternalꢀcomponents.ꢀWhenꢀconfiguredꢀ
forꢀdualꢀoutputꢀoperation,ꢀtheꢀLTC3541-2’sꢀautoꢀstart-upꢀ
featureꢀwillꢀbringꢀtheꢀ1.875Vꢀbuckꢀoutputꢀintoꢀregulationꢀ
inꢀaꢀcontrolledꢀmanner,ꢀpriorꢀtoꢀenablingꢀtheꢀ1.5VꢀVLDOꢀ
outputꢀwithoutꢀtheꢀneedꢀforꢀexternalꢀpinꢀcontrol.ꢀTheꢀ
1.5VꢀVLDO/linearꢀregulatorꢀoutputꢀpriorꢀtoꢀ1.875Vꢀbuckꢀ
outputꢀsequencingꢀmayꢀalsoꢀbeꢀobtainedꢀviaꢀexternalꢀpinꢀ
control.ꢀTheꢀinputꢀvoltageꢀrangeꢀisꢀideallyꢀsuitedꢀforꢀLi-Ionꢀ
batteryꢀapplicationsꢀpoweringꢀsub-3.3Vꢀlogicꢀfromꢀ5Vꢀorꢀ
3.3Vꢀrails.
■
Regulator
ꢀ
ꢀ
Auto Start-Up Powers Buck Output Prior to VLDO/
Linear Regulator 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: 1.875V
ꢀ VLDO Input Voltage Range (LV : 1.6V to 5.5V)
IN
ꢀ FixedꢀVLDO Output Voltage: 1.5V
ꢀ SelectableꢀFixedꢀFrequency,ꢀPulse-SkipꢀOperation
ꢀ orꢀBurstꢀMode®ꢀOperation
■
ꢀ Short-CircuitꢀProtected
ꢀ CurrentꢀModeꢀOperationꢀforꢀExcellentꢀLineꢀandꢀLoadꢀ
■
Theꢀsynchronousꢀbuckꢀconverterꢀprovidesꢀaꢀhighꢀefficiencyꢀ
output,ꢀtypicallyꢀ90%.ꢀItꢀcanꢀprovideꢀupꢀtoꢀ500mAꢀofꢀoutputꢀ
currentꢀwhileꢀswitchingꢀatꢀ2.25MHz,ꢀallowingꢀtheꢀuseꢀofꢀ
smallꢀsurfaceꢀmountꢀinductorsꢀandꢀcapacitors.ꢀAꢀmode-
selectꢀpinꢀallowsꢀBurstꢀModeꢀoperationꢀtoꢀbeꢀenabledꢀforꢀ
higherꢀefficiencyꢀatꢀlightꢀloadꢀcurrents,ꢀorꢀdisabledꢀforꢀlowerꢀ
noise,ꢀconstantꢀfrequencyꢀoperation.ꢀ
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
buckꢀregulatorꢀoutputꢀorꢀaꢀseparateꢀsupply.
APPLICATIO S
■
ꢀ DigitalꢀCameras
■
ꢀ CellularꢀPhones
IN
■
ꢀ PCꢀCards
■
ꢀ WirelessꢀandꢀDSLꢀModems
, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology
■
ꢀ OtherꢀPortableꢀPowerꢀSystems
Corporation. VLDO is a trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Protected by U.S. Patents, including 5481178, 6611131, 6304066, 6498466, 6580258.
U
Buck (Burst) Efficiency vs Load Current
TYPICAL APPLICATIO
100
1
V
= 3V
V
IN
IN
90
2.9V TO 5.5V
EFFICIENCY
80
0.1
70
SW
ENVLDO
MODE
60
50
V
IN
POWER LOSS
2.2µH
0.01
0.001
0.0001
LTC3541-2
ENBUCK GND
40
30
20
10
0
V
OUT1
V
OUT
1.875V
200mA
V
OUT2
1.5V
LV
LV
IN
OUT
300mA
PGND
10µF
2.2µF
35412 TA01a
1
10
100
1000
LOAD CURRENT (mA)
35412 TA01b
35412fb
ꢀ
ꢀ ENVLDO,ꢀENBUCK,ꢀMODE,ꢀSWꢀ......–0.3VꢀtoꢀV ꢀ+ꢀ0.3V
IN
LTC3541-2
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
V
1
2
3
4
5
10 SW
IN
IN
IN
ENBUcK
9
8
7
6
ENVLDO
ꢀ LV ꢀ–ꢀV ꢀ..........................................................<0.3V
IN
IN
11
V
MODE
GND
OUT
Nc
PinꢀVoltages:
LV
LV
IN
OUT
LinearꢀRegulatorꢀI
ꢀ(100ms)ꢀ(Noteꢀ9)ꢀ......100mA
OUT(MAX)
DD PAcKAGE
10-LEAD (3mm × 3mm) PLASTIc DFN
OperatingꢀAmbientꢀTemperatureꢀRangeꢀ
(Noteꢀ2).................................................... –40°Cꢀtoꢀ85°C
JunctionꢀTemperatureꢀ(Notesꢀ5,ꢀ10)...................... 125°C
StorageꢀTemperatureꢀRange................... –65°Cꢀtoꢀ125°C
ꢀ
ꢀ
T
ꢀ=ꢀ125°C,ꢀθ ꢀ=ꢀ43°C/W
JA
EXPOSEDꢀPADꢀ(PINꢀ11)ꢀISꢀPGND,ꢀMUSTꢀBEꢀSOLDEREDꢀTOꢀPCB
JMAX
ORDERꢀPARTꢀNUMBER
LTC3541EDD-2
DDꢀPARTꢀMARKING
LCHQ
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 (Note 2)
SYMBOL
PARAMETER
PeakꢀInductorꢀCurrent
CONDITIONS
V ꢀ=ꢀ4.2Vꢀ(Noteꢀ8)
IN
MIN
0.8
TYP
0.95
MAX
1.25
UNITS
Aꢀ
I
PK
●
●
V
V
InputꢀVoltageꢀRange
(Noteꢀ4)
2.7
5.5
0.4
V
IN
BuckꢀV ꢀLineꢀRegulationꢀꢀ
V ꢀ=ꢀ2.7Vꢀtoꢀ5.5V,ꢀENBUCKꢀ=ꢀV ,ꢀꢀ
0.04
2.2
2.2
0.8
%/V
IN(LINEREG)
IN
IN
IN
ENVLDOꢀ=ꢀ0V,ꢀMODEꢀ=ꢀV ꢀ(Noteꢀ6)
IN
VLDOꢀV ꢀLineꢀRegulationꢀꢀ
V ꢀ=ꢀ2.9Vꢀtoꢀ5.5V,ꢀLV ꢀ=ꢀ1.5V,ꢀ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
V ꢀ=ꢀ2.9Vꢀtoꢀ5.5V,ꢀLV ꢀ=ꢀ1.5V,ꢀENBUCKꢀ=ꢀ0V,ꢀꢀ
IN OUT
ENVLDOꢀ=ꢀV ,ꢀI
IN
Regulationꢀ(ReferredꢀtoꢀLV
)
ꢀ=ꢀ10mA
OUT
IN OUT(LDO)
LV
LV ꢀLineꢀRegulationꢀꢀ
LV ꢀ=ꢀ1.6Vꢀtoꢀ5.5V,ꢀV ꢀ=ꢀ5.5V,ꢀLV ꢀ=ꢀ1.5V,ꢀꢀ
IN(LINEREG)
IN
IN IN OUT
(ReferredꢀtoꢀLV
)
ENBUCKꢀ=ꢀV ,ꢀENVLDOꢀ=ꢀV ,ꢀMODEꢀ=ꢀV ,ꢀꢀ
OUT
IN
IN
IN
I
ꢀ=ꢀ100mA
OUT(VLDO)
VLDO
LV ꢀ–ꢀLV ꢀDropoutꢀVoltage LV ꢀ=ꢀ1.5V,ꢀ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 ꢀ=ꢀ1.875V,ꢀLV ꢀ=ꢀ1.5V,ꢀ
0.25
0.5
0.5
OUT(VLDO)
IN
OUT
ENBUCKꢀ=ꢀV ,ꢀENVLDOꢀ=ꢀV ,ꢀMODEꢀ=ꢀV
IN
IN
IN
LinearꢀRegulatorꢀOutputꢀLoadꢀꢀ
Regulation
I
ꢀ=ꢀ1mAꢀ–ꢀ30mA,ꢀLV ꢀ=ꢀ1.5V,ꢀꢀ
0.25ꢀ
%
OUT(LDO)
OUT
ENBUCKꢀ=ꢀ0V,ꢀENVLDOꢀ=ꢀV
IN
V
V
ReferenceꢀRegulationꢀVoltageꢀ ENBUCKꢀ=ꢀV ,ꢀENVLDOꢀ=ꢀ0V,ꢀT ꢀ=ꢀ25°C
1.837
1.833
1.828
1.47
1.875
1.875
1.875
1.5
1.913
1.917
1.922
1.53
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
IN
A
ReferenceꢀRegulationꢀVoltageꢀ ENBUCKꢀ=ꢀ0V,ꢀENVLDOꢀ=ꢀV ,ꢀT ꢀ=ꢀ25°C
LVOUT
IN
A
(Noteꢀ7)
ENBUCKꢀ=ꢀ0V,ꢀENVLDOꢀ=ꢀV ,ꢀ0°Cꢀ≤ꢀT ꢀ≤ꢀ85°C
1.466
1.462
1.5
1.534
1.538
IN
A
ENBUCKꢀ=ꢀ0V,ꢀENVLDOꢀ=ꢀV ,ꢀ–40°Cꢀ≤ꢀT ꢀ≤ꢀ85°C
1.5
IN
A
35412fb
ꢁ
LTC3541-2
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 (Note 2)
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
I
Buckꢀ+ꢀVLDOꢀꢀ
LV ꢀ=ꢀ1.875V,ꢀLV ꢀ=ꢀ1.5V,ꢀENBUCKꢀ=ꢀV ,ꢀꢀ
85
µA
S
IN
OUT
IN
BurstꢀModeꢀSleepꢀꢀ
ENVLDOꢀ=ꢀV ,ꢀMODEꢀ=ꢀ0V,ꢀI
ꢀ=ꢀ10µA,ꢀꢀ
IN
OUT(VLDO)
V ꢀQuiescentꢀCurrent
IN
V
ꢀ=ꢀ2.11V
VOUT
Buckꢀ+ꢀVLDOꢀꢀ
LV ꢀ=ꢀ1.875V,ꢀLV ꢀ=ꢀ1.5V,ꢀENBUCKꢀ=ꢀV ,ꢀꢀ
315
300
55
µA
µA
µA
µA
µA
IN
OUT
IN
BurstꢀModeꢀActiveꢀ
ENVLDOꢀ=ꢀV ,ꢀMODEꢀ=ꢀ0V,ꢀI
ꢀ=ꢀ10µA,ꢀꢀ
IN
OUT(VLDO)
V ꢀQuiescentꢀCurrent
V
ꢀ=ꢀ1.64V
IN
VOUT
Buckꢀ+ꢀVLDOꢀ
LV ꢀ=ꢀ1.875V,ꢀLV ꢀ=ꢀ1.5V,ꢀENBUCKꢀ=ꢀV ,ꢀꢀ
IN
OUT
IN
Pulse-SkipꢀModeꢀActiveꢀ
ENVLDOꢀ=ꢀV ,ꢀMODEꢀ=ꢀV ,ꢀI
ꢀ=ꢀ10µA,ꢀꢀ
IN
IN OUT(VLDO)
V ꢀQuiescentꢀCurrent
V
V
ꢀ=ꢀ1.64V
IN
VOUT
Buckꢀ
ꢀ=ꢀ2.11V,ꢀI
ꢀ=ꢀ0A,ꢀENBUCKꢀ=ꢀV ,ꢀ
VOUT
OUT(BUCK)
IN
BurstꢀModeꢀSleepꢀ
ENVLDOꢀ=ꢀ0V,ꢀMODEꢀ=ꢀ0V
V ꢀQuiescentꢀCurrent
IN
Buckꢀ
V
ꢀ=ꢀ1.64V,ꢀI
ꢀ=ꢀ0A,ꢀENBUCKꢀ=ꢀV ,ꢀ
300
285
VOUT
OUT(BUCK)
IN
BurstꢀModeꢀActiveꢀ
ENVLDOꢀ=ꢀ0V,ꢀMODEꢀ=ꢀ0V
V ꢀQuiscentꢀCurrent
IN
Buckꢀ
V
ꢀ=ꢀ1.64V,ꢀI
ꢀ=ꢀ0A,ꢀENBUCKꢀ=ꢀV ,ꢀ
VOUT
OUT(BUCK)
IN
Pulse-SkipꢀModeꢀActiveꢀ
ENVLDOꢀ=ꢀ0V,ꢀMODEꢀ=ꢀV
IN
V ꢀQuiescentꢀCurrent
IN
LinearꢀRegulatorꢀV ꢀQuiescentꢀ LV ꢀ=ꢀ1.5V,ꢀENBUCKꢀ=ꢀ0V,ꢀENVLDOꢀ=ꢀV ,ꢀꢀ
50
2.5
0.1
µA
µA
µA
IN
OUT
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:ꢀTheꢀLTC3541-2ꢀisꢀtestedꢀinꢀaꢀproprietaryꢀtestꢀmodeꢀthatꢀconnectsꢀ
ꢀtoꢀtheꢀoutputꢀofꢀtheꢀerrorꢀamplifier.ꢀForꢀtheꢀreferenceꢀregulationꢀ
andꢀlineꢀregulationꢀtests,ꢀtheꢀoutputꢀofꢀtheꢀerrorꢀamplifierꢀisꢀsetꢀtoꢀtheꢀ
midpoint.ꢀForꢀtheꢀloadꢀregulationꢀtest,ꢀtheꢀoutputꢀofꢀtheꢀerrorꢀamplifierꢀisꢀ
drivenꢀtoꢀtheꢀminimumꢀandꢀmaximumꢀofꢀtheꢀsignalꢀrange.
Note 1:ꢀStressesꢀbeyondꢀthoseꢀlistedꢀunderꢀAbsoluteꢀMaximumꢀRatingsꢀ
mayꢀcauseꢀpermanentꢀdamageꢀtoꢀtheꢀdevice.ꢀExposureꢀtoꢀanyꢀAbsoluteꢀ
MaximumꢀRatingꢀconditionꢀforꢀextendedꢀperiodsꢀmayꢀaffectꢀdeviceꢀ
reliabilityꢀandꢀlifetime.
V
BUCKFB
Note 2:ꢀTheꢀLTC3541-2ꢀisꢀguaranteedꢀtoꢀmeetꢀperformanceꢀspecificationsꢀ
fromꢀ0°Cꢀtoꢀ85°C.ꢀVLDO/linearꢀregulatorꢀoutputꢀisꢀtestedꢀandꢀspecifiedꢀ
underꢀpulseꢀloadꢀconditionsꢀsuchꢀthatꢀT ꢀ≈ꢀT ,ꢀandꢀareꢀ100%ꢀproductionꢀ
Note 7:ꢀMeasurementꢀmadeꢀinꢀclosedꢀloopꢀlinearꢀregulatorꢀconfigurationꢀ
withꢀLV ꢀ=ꢀ1.5V,ꢀI
ꢀ=ꢀ10µA.
LOAD
OUT
J
A
testedꢀatꢀ25°C.ꢀSpecificationsꢀoverꢀtheꢀ–40°Cꢀtoꢀ85°Cꢀoperatingꢀ
temperatureꢀrangeꢀareꢀassuredꢀbyꢀdesign,ꢀcharacterizationꢀandꢀcorrelationꢀ
withꢀstatisticalꢀprocessꢀcontrols.
Note 8:ꢀMeasurementꢀmadeꢀinꢀaꢀproprietaryꢀtestꢀmodeꢀwithꢀslopeꢀ
compensationꢀdisabled.
Note 9:ꢀMeasurementꢀisꢀassuredꢀbyꢀdesign,ꢀ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
35412fb
ꢂ
LTC3541-2
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)
2
3
5
6
0.1
1
10
100
1000
2
3
4
5
6
LOAD CURRENT (mA)
INPUT VOLTAGE (V)
35412 G03
35412 G01
35412 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
100
80
250
200
150
100
50
V
= 2.7V
V
= 3.6V
IN
IN
V
= 3.6V
IN
90
80
70
60
50
40
30
20
10
0
I
I
= 0
LOAD_BUCK
BIAS VIN LVIN LOAD
= I + I
– I
V
= 3V
IN
V
= 4.2V
IN
V
= 3.6V
IN
60
V
= 4.2V
IN
40
20
0
0
0
100
150
200
250
300
0.1
1
10
100
1000
50
1
10
100
0.1
1000
LOAD CURRENT (mA)
LOAD CURRENT (mA)
LOAD CURRENT (mA)
35412 G04
35412 G05
35412 G06
Output (Auto Start-Up Sequence,
Buck in Pulse Skip) vs Time
Oscillator Frequency
vs Temperature
2.50
V
= 3.6V
IN
2.45
2.40
2.35
2.30
2.25
2.20
2.15
2.10
2.05
2.00
V
OUT
1V/DIV
LV
1V/DIV
OUT
V
IN
2V/DIV
35412 G07
I
I
= 200mA
LVOUT
2ms/DIV
VOUT
= 300mA
–50
0
25
50
75 100 125
–25
TEMPERATURE (°C)
35412 G08
35412fb
ꢃ
LTC3541-2
W U
TYPICAL PERFOR A CE CHARACTERISTICS
Oscillator Frequency
vs Supply Voltage
VLDO/Linear Regulator Reference
vs Temperature
Buck Reference 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
2.5
2.4
2.3
2.2
2.1
2.0
V
= 3.6V
V
= 3.6V
V
= 3.6V
IN
IN
IN
–50
0
25
50
75 100 125
–25
50
TEMPERATURE (°C)
125
3
4
5
6
–50
0
25
75
–25
100
TEMPERATURE (°C)
SUPPLY VOLTAGE (V)
35412 G19
35412 G09
35412 G20
Buck (Pulse Skip) Load Step from
1mA to 500mA
RDS(0N) vs Temperature
Buck (Burst) and VLDO Output
0.700
0.600
0.500
0.400
0.300
0.200
0.100
0
L
V
VOUT
OUT
10mV/DIV
100mV/DIV
AC COUPLED
AC COUPLED
I
V
L
OUT
500mA/DIV
10mV/DIV
SYNCH SWITCH
MAIN SWITCH
AC COUPLED
I
LOAD
500mA/DIV
V
V
V
= 2.5V
= 3.6V
= 5.5V
35412 G21
35412 G11
IN
IN
IN
V
= 3.6V
2µs/DIV
V
V
I
= 3.6V
40µs/DIV
IN
IN
OUT
LOAD
LV
V
= 1.5V
= 1.875V
= 1mA TO 500mA
OUT
= 1.875V
= 50mA
OUT
I
50
TEMPERATURE (°C)
100 125
–50 –25
0
25
75
LOAD
Burst Mode OPERATION
35412 G10
Buck (Burst) Load Step from
1mA to 500mA
VLDO Load Step from 1mA to
300mA
VLDO Load Step from 100mA to
300mA
V
OUT
100mV/DIV
LV
OUT
LV
OUT
AC COUPLED
20mV/DIV
20mV/DIV
AC COUPLED
AC COUPLED
I
L
500mA/DIV
I
LOAD
I
I
LOAD
250mA/DIV
LOAD
250mA/DIV
500mA/DIV
35412 G12
35412 G13
35412 G14
V
V
I
= 3.6V
40µs/DIV
V
V
I
= 3.6V
200µs/DIV
V
= 3.6V
200µs/DIV
IN
OUT
IN
OUT
IN
= 1.875V
= 1.5V
LV
I
= 1.5V
OUT
= 1mA TO 500mA
= 1mA TO 300mA
= 100mA TO 300mA
LOAD
LOAD
LOAD
35412fb
ꢄ
LTC3541-2
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
50mA/DIV
I
LOAD
50mA/DIV
35412 G15
35412 G16
V
= 3.6V
40µs/DIV
V
= 3.6V
IN
40µs/DIV
IN
LV
= 1.5V
LV
= 1.5V
OUT
OUT
I
= 1mA
I
= 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
LOAD
I
50mA/DIV
LOAD
50mA/DIV
35412 G18
35412 G17
V
= 3.6V
40µs/DIV
V
= 3.6V
40µs/DIV
IN
IN
LV
I
= 1.5V
LV
I
= 1.5V
OUT
OUT
= 30mA
= 1mA
LOAD
LOAD
35412fb
ꢅ
LTC3541-2
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
ofꢀtheꢀLTC3541-2.
NC(Pin4):ꢀNotꢀConnected.ꢀThisꢀpinꢀmustꢀnotꢀbeꢀconnectedꢀ
orꢀcapacitivelyꢀloaded.
Table 1. LTC3541-2 Control Pin Truth Table
LV
(Pin 5):ꢀVLDO/LinearꢀRegulatorꢀOutputꢀPin.ꢀThisꢀ
OUT
PIN NAME
OPERATIONAL DESCRIPTION
pinꢀprovidesꢀtheꢀregulatedꢀoutputꢀvoltageꢀfromꢀtheꢀVLDOꢀ
ENBUCK ENVLDO MODE
orꢀlinearꢀregulator.
0
0
0
1
X
X
LTC3541-2ꢀPoweredꢀDown
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-SkipꢀModeꢀOperation
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
ModeꢀOperation
35412fb
ꢆ
LTC3541-2
U
U
W
FU CTIO AL BLOCK DIAGRA
V
I
= 1.875V
= 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
= 1.5V
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
35412 F01
Figure 1. LTC3541-2 Functional Block Diagram
35412fb
ꢇ
LTC3541-2
U
OPERATIO
TheꢀLTC3541-2ꢀcontainsꢀaꢀhighꢀefficiencyꢀsynchronousꢀ
buckꢀconverter,ꢀaꢀveryꢀlowꢀdropoutꢀregulatorꢀ(VLDO),ꢀandꢀ
aꢀlinearꢀregulatorꢀthatꢀcanꢀbeꢀusedꢀtoꢀprovideꢀupꢀtoꢀtwoꢀ
outputꢀvoltagesꢀfromꢀaꢀsingleꢀinputꢀvoltageꢀmakingꢀtheꢀ
LTC3541-2ꢀidealꢀforꢀapplicationsꢀwithꢀlimitedꢀboardꢀspace.ꢀ
Theꢀcombinationꢀandꢀconfigurationꢀofꢀtheseꢀmajorꢀblocksꢀ
withinꢀtheꢀLTC3541-2ꢀisꢀdeterminedꢀbyꢀwayꢀofꢀtheꢀcontrolꢀ
pinsꢀENBUCKꢀandꢀENVLDOꢀasꢀdefinedꢀinꢀTableꢀ1.
Buck Regulator Control Loop
TheꢀLTC3541-2ꢀinternalꢀbuckꢀregulatorꢀusesꢀaꢀconstantꢀ
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,ꢀtheꢀLTC3541-2ꢀenablesꢀtheꢀbuckꢀ
converterꢀ toꢀ efficientlyꢀ reduceꢀ theꢀ voltageꢀ providedꢀ atꢀ
theꢀV ꢀinputꢀpinꢀtoꢀanꢀoutputꢀvoltageꢀofꢀ1.875Vꢀwhichꢀ
IN
isꢀsetꢀbyꢀanꢀinternalꢀfeedbackꢀresistorꢀnetwork.ꢀTheꢀbuckꢀ
regulatorꢀcanꢀbeꢀconfiguredꢀforꢀPulse-SkipꢀorꢀBurstꢀModeꢀ
operationꢀbyꢀdrivingꢀtheꢀMODEꢀpinꢀtoꢀaꢀlogicꢀhighꢀorꢀlogicꢀ
lowꢀrespectively.ꢀTheꢀbuckꢀregulatorꢀisꢀcapableꢀofꢀprovid-
ingꢀaꢀmaximumꢀoutputꢀcurrentꢀofꢀ500mA,ꢀwhichꢀmustꢀbeꢀ
takenꢀintoꢀconsiderationꢀwhenꢀusingꢀtheꢀbuckꢀregulatorꢀ
toꢀprovideꢀtheꢀpowerꢀforꢀbothꢀtheꢀVLDOꢀregulatorꢀandꢀforꢀ
externalꢀloads.ꢀ
Theꢀpeakꢀinductorꢀcurrentꢀisꢀdeterminedꢀbyꢀcomparingꢀtheꢀ
buckꢀfeedbackꢀsignalꢀtoꢀanꢀinternalꢀ0.8Vꢀreference.ꢀWhenꢀ
theꢀloadꢀcurrentꢀincreases,ꢀtheꢀoutputꢀofꢀtheꢀbuckꢀandꢀ
henceꢀtheꢀbuckꢀfeedbackꢀsignalꢀdecrease.ꢀThisꢀdecreaseꢀ
causesꢀtheꢀpeakꢀinductorꢀcurrentꢀtoꢀincreaseꢀuntilꢀtheꢀaver-
ageꢀinductorꢀcurrentꢀmatchesꢀtheꢀloadꢀcurrent.ꢀWhileꢀtheꢀ
mainꢀswitchꢀisꢀoff,ꢀtheꢀsynchronousꢀswitchꢀisꢀturnedꢀonꢀ
untilꢀeitherꢀtheꢀinductorꢀcurrentꢀstartsꢀtoꢀreverseꢀdirectionꢀ
orꢀtheꢀbeginningꢀofꢀaꢀnewꢀclockꢀcycle.
WithꢀtheꢀENBUCKꢀpinꢀdrivenꢀtoꢀaꢀlogicꢀlowꢀandꢀENVLDOꢀ
drivenꢀtoꢀaꢀlogicꢀhigh,ꢀtheꢀLTC3541-2ꢀenablesꢀtheꢀlinearꢀ
regulator,ꢀprovidingꢀaꢀlowꢀnoiseꢀregulatedꢀoutputꢀvoltageꢀ
WhenꢀtheꢀMODEꢀpinꢀisꢀdrivenꢀtoꢀaꢀlogicꢀlow,ꢀtheꢀLTC3541-2ꢀ
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.
ofꢀ1.5VꢀatꢀtheꢀLV ꢀpinꢀwhileꢀdrawingꢀminimalꢀquiescentꢀ
OUT
currentꢀfromꢀtheꢀV ꢀinputꢀpin.ꢀThisꢀfeatureꢀallowsꢀoutputꢀ
IN
voltageꢀLV ꢀtoꢀbeꢀbroughtꢀintoꢀregulationꢀwithoutꢀtheꢀ
OUT
presenceꢀofꢀtheꢀLV ꢀvoltage.ꢀ
IN
Withꢀ theꢀ ENBUCKꢀ andꢀ ENVLDOꢀ pinsꢀ bothꢀ drivenꢀ toꢀ aꢀ
logicꢀ high,ꢀ theꢀ LTC3541-2ꢀ enablesꢀ theꢀ highꢀ efficiencyꢀ
buckꢀconverterꢀandꢀVLDO,ꢀprovidingꢀdualꢀoutputꢀopera-
tionꢀfromꢀaꢀsingleꢀinputꢀvoltage.ꢀWhenꢀconfiguredꢀinꢀthisꢀ
manner,ꢀtheꢀLTC3541-2’sꢀautoꢀstart-upꢀsequencingꢀfeatureꢀ
willꢀbringꢀtheꢀbuckꢀoutputꢀ(1.875V)ꢀintoꢀregulationꢀinꢀaꢀ
controlledꢀmannerꢀpriorꢀtoꢀenablingꢀtheꢀVLDOꢀregulatorꢀ
(1.5V)ꢀwithoutꢀtheꢀneedꢀforꢀexternalꢀpinꢀcontrol.ꢀAꢀdetailedꢀ
discussionꢀofꢀtheꢀtransitionsꢀbetweenꢀtheꢀVLDOꢀregula-
torꢀandꢀlinearꢀregulatorꢀcanꢀbeꢀfoundꢀinꢀtheꢀVLDO/Linearꢀ
RegulatorꢀLoopꢀsection.ꢀ
35412fb
ꢈ
LTC3541-2
U
OPERATIO
WhenꢀtheꢀMODEꢀpinꢀisꢀdrivenꢀtoꢀaꢀlogicꢀhighꢀtheꢀLTC3541-2ꢀ
operatesꢀinꢀPulse-Skipꢀmodeꢀforꢀlowꢀoutputꢀvoltageꢀripple.ꢀ
Inꢀthisꢀmode,ꢀtheꢀLTC3541-2ꢀcontinuesꢀtoꢀswitchꢀatꢀaꢀ
constantꢀfrequencyꢀdownꢀtoꢀveryꢀlowꢀcurrents,ꢀwhereꢀitꢀ
willꢀbeginꢀskippingꢀpulsesꢀusedꢀtoꢀcontrolꢀtheꢀmainꢀ(top)ꢀ
switchꢀtoꢀmaintainꢀtheꢀproperꢀaverageꢀinductorꢀcurrent.
TheꢀN-channelꢀMOSFET,ꢀincorporatedꢀinꢀtheꢀVLDOꢀregula-
tor,ꢀhasꢀitsꢀdrainꢀconnectedꢀtoꢀtheꢀLV ꢀpinꢀasꢀshownꢀinꢀ
IN
Figureꢀ1.ꢀToꢀensureꢀreliableꢀoperation,ꢀtheꢀLV ꢀvoltageꢀ
IN
mustꢀbeꢀstableꢀbeforeꢀtheꢀVLDOꢀregulatorꢀisꢀenabled.ꢀForꢀ
theꢀcaseꢀwhereꢀtheꢀvoltageꢀonꢀtheꢀLV ꢀpinꢀisꢀsuppliedꢀbyꢀ
IN
theꢀbuckꢀregulator,ꢀtheꢀinternalꢀpowerꢀsupplyꢀsequenc-
ingꢀlogicꢀassuresꢀvoltagesꢀareꢀappliedꢀinꢀtheꢀappropriateꢀ
manner.ꢀForꢀtheꢀcaseꢀwhereꢀanꢀexternalꢀsupplyꢀisꢀusedꢀtoꢀ
Ifꢀtheꢀinputꢀsupplyꢀvoltageꢀisꢀdecreasedꢀtoꢀaꢀvalueꢀap-
proachingꢀtheꢀoutputꢀvoltage,ꢀtheꢀdutyꢀcycleꢀofꢀtheꢀbuckꢀ
isꢀincreasedꢀtowardꢀmaximumꢀon-timeꢀandꢀ100%ꢀdutyꢀ
cycle.ꢀTheꢀoutputꢀvoltageꢀwillꢀthenꢀbeꢀdeterminedꢀbyꢀtheꢀ
inputꢀvoltageꢀminusꢀtheꢀvoltageꢀdropꢀacrossꢀtheꢀmainꢀ
switchꢀandꢀtheꢀinductor.
powerꢀtheꢀLV ꢀpin,ꢀtheꢀexternallyꢀsuppliedꢀLV ꢀvoltageꢀ
IN
IN
mustꢀbeꢀstableꢀ1msꢀbeforeꢀtheꢀENVLDOꢀisꢀbroughtꢀfromꢀ
aꢀlowꢀtoꢀaꢀhigh.ꢀFurther,ꢀtheꢀexternallyꢀsuppliedꢀLV ꢀmustꢀ
IN
beꢀreducedꢀinꢀconjunctionꢀwithꢀV ꢀwheneverꢀV ꢀisꢀpulledꢀ
IN
IN
lowꢀorꢀremoved.
VLDO/Linear Regulator Loop
Theꢀlinearꢀregulatorꢀisꢀdesignedꢀtoꢀprovideꢀaꢀlowerꢀoutputꢀ
currentꢀthanꢀthatꢀavailableꢀfromꢀtheꢀVLDOꢀregulator.ꢀTheꢀ
linearꢀregulator’sꢀoutput,ꢀpassꢀtransistorꢀhasꢀitsꢀdrainꢀtiedꢀ
InꢀtheꢀLTC3541-2,ꢀtheꢀVLDOꢀandꢀlinearꢀregulatorꢀloopsꢀ
consistꢀofꢀanꢀamplifierꢀandꢀN-channelꢀMOSFETꢀoutputꢀ
stagesꢀthatꢀservoꢀtheꢀoutputꢀtoꢀmaintainꢀaꢀregulatorꢀoutputꢀ
toꢀtheꢀV ꢀrail.ꢀThisꢀallowsꢀtheꢀlinearꢀregulatorꢀtoꢀbeꢀturnedꢀ
IN
onꢀpriorꢀto,ꢀandꢀindependentꢀof,ꢀtheꢀbuckꢀregulatorꢀwhichꢀ
ordinarilyꢀdrivesꢀtheꢀVLDOꢀregulator.ꢀTheꢀlinearꢀregulatorꢀ
isꢀprovidedꢀwithꢀthermalꢀprotectionꢀthatꢀisꢀdesignedꢀtoꢀ
disableꢀtheꢀlinearꢀregulatorꢀfunctionꢀwhenꢀtheꢀoutputꢀpassꢀ
transistor’sꢀjunctionꢀtemperatureꢀreachesꢀapproximatelyꢀ
160°C.ꢀ Inꢀ additionꢀ toꢀ thermalꢀ protection,ꢀ short-circuitꢀ
detectionꢀisꢀprovidedꢀtoꢀdisableꢀtheꢀlinearꢀregulatorꢀfunc-
tionꢀwhenꢀaꢀshort-circuitꢀconditionꢀisꢀsensed.ꢀThisꢀcircuitꢀ
isꢀdesignedꢀsuchꢀthatꢀanꢀoutputꢀcurrentꢀofꢀapproximatelyꢀ
120mAꢀcanꢀbeꢀprovidedꢀbeforeꢀthisꢀcircuitꢀwillꢀtrigger.ꢀAsꢀ
detailedꢀinꢀtheꢀElectricalꢀCharacteristics,ꢀtheꢀlinearꢀregulatorꢀ
willꢀbeꢀoutꢀofꢀregulationꢀwhenꢀthisꢀeventꢀoccurs.ꢀBothꢀtheꢀ
thermalꢀandꢀshort-circuitꢀfaultsꢀareꢀtreatedꢀasꢀcatastrophicꢀ
faultꢀconditions.ꢀTheꢀLTC3541-2ꢀwillꢀbeꢀresetꢀuponꢀtheꢀ
detectionꢀofꢀeitherꢀevent.
voltage,ꢀLV .ꢀTheꢀinternalꢀreferenceꢀvoltageꢀprovidedꢀtoꢀ
OUT
theꢀamplifierꢀisꢀ0.4Vꢀallowingꢀforꢀaꢀwideꢀrangeꢀofꢀoutputꢀ
voltages.ꢀLoopꢀconfigurationsꢀenablingꢀtheꢀVLDOꢀorꢀtheꢀ
linearꢀregulatorꢀareꢀstableꢀwithꢀanꢀoutputꢀcapacitanceꢀasꢀ
lowꢀasꢀ2.2µFꢀandꢀasꢀhighꢀasꢀ100µF.ꢀBothꢀtheꢀVLDOꢀandꢀ
theꢀlinearꢀregulatorsꢀareꢀcapableꢀofꢀoperatingꢀwithꢀanꢀinputꢀ
voltage,ꢀV ,ꢀasꢀlowꢀasꢀ2.9V.ꢀ
IN
TheꢀVLDOꢀregulatorꢀisꢀdesignedꢀtoꢀprovideꢀupꢀtoꢀ300mAꢀ
ofꢀoutputꢀcurrentꢀatꢀaꢀveryꢀlowꢀLV ꢀtoꢀLV ꢀvoltage.ꢀThisꢀ
IN
OUT
allowsꢀaꢀclean,ꢀsecondary,ꢀanalogꢀsupplyꢀvoltageꢀtoꢀbeꢀ
providedꢀwithꢀaꢀminimumꢀdropꢀinꢀefficiency.ꢀTheꢀVLDOꢀ
regulatorꢀisꢀprovidedꢀwithꢀthermalꢀprotectionꢀthatꢀisꢀde-
signedꢀtoꢀdisableꢀtheꢀVLDOꢀfunctionꢀwhenꢀtheꢀoutput,ꢀpassꢀ
transistor’sꢀjunctionꢀtemperatureꢀreachesꢀapproximatelyꢀ
160°C.ꢀInꢀadditionꢀtoꢀthermalꢀprotection,ꢀshort-circuitꢀ
detectionꢀisꢀprovidedꢀtoꢀdisableꢀtheꢀVLDOꢀfunctionꢀwhenꢀaꢀ
short-circuitꢀconditionꢀisꢀsensed.ꢀThisꢀcircuitꢀisꢀdesignedꢀ
suchꢀthatꢀanꢀoutputꢀcurrentꢀofꢀapproximatelyꢀ1Aꢀcanꢀbeꢀ
providedꢀbeforeꢀthisꢀcircuitꢀwillꢀtrigger.ꢀAsꢀdetailedꢀinꢀtheꢀ
ElectricalꢀCharacteristics,ꢀtheꢀVLDOꢀregulatorꢀwillꢀbeꢀoutꢀ
ofꢀregulationꢀwhenꢀthisꢀeventꢀoccurs.ꢀBothꢀtheꢀthermalꢀ
andꢀshort-circuitꢀfaults,ꢀwhenꢀdetected,ꢀareꢀtreatedꢀasꢀ
catastrophicꢀ faultꢀ conditions.ꢀ Theꢀ LTC3541-2ꢀ willꢀ beꢀ
resetꢀuponꢀtheꢀdetectionꢀofꢀeitherꢀevent.
TheꢀN-channelꢀMOSFET,ꢀincorporatedꢀinꢀtheꢀlinearꢀregu-
lator,ꢀhasꢀitsꢀdrainꢀconnectedꢀtoꢀtheꢀV ꢀpinꢀasꢀshownꢀinꢀ
IN
Figureꢀ1.ꢀTheꢀsizeꢀofꢀtheseꢀMOSFETsꢀandꢀtheirꢀassociatedꢀ
powerꢀbussingꢀisꢀdesignedꢀtoꢀaccomodateꢀ30mAꢀofꢀDCꢀ
current.ꢀCurrentsꢀaboveꢀthisꢀvalueꢀcanꢀbeꢀsupportedꢀforꢀ
shortꢀ periodsꢀ asꢀ stipulatedꢀ inꢀ theꢀ Absoluteꢀ Maximumꢀ
Ratings.
35412fb
ꢀ0
LTC3541-2
U
OPERATIO
TransitioningꢀfromꢀlinearꢀregulatorꢀmodeꢀtoꢀVLDOꢀmode,ꢀ
accomplishedꢀbyꢀbringingꢀENBUCKꢀfromꢀaꢀlogicꢀlowꢀtoꢀaꢀ
logicꢀhighꢀwhileꢀENVLDOꢀisꢀaꢀlogicꢀhigh,ꢀisꢀdesignedꢀtoꢀbeꢀ
asꢀseamlessꢀandꢀtransientꢀfreeꢀasꢀpossible.ꢀTheꢀpreciseꢀ
Inꢀaꢀsimilarꢀmanner,ꢀtransitioningꢀfromꢀVLDOꢀmodeꢀtoꢀ
linearꢀregulatorꢀmode,ꢀaccomplishedꢀbyꢀbringingꢀENBUCKꢀ
fromꢀaꢀhighꢀlowꢀtoꢀaꢀlogicꢀlowꢀwhileꢀENVLDOꢀisꢀaꢀlogicꢀ
high,ꢀisꢀdesignedꢀtoꢀbeꢀasꢀseamlessꢀandꢀtransientꢀfreeꢀasꢀ
transientꢀresponseꢀofꢀLV ꢀdueꢀtoꢀthisꢀtransitionꢀisꢀaꢀ
possible.ꢀAgain,ꢀtheꢀpreciseꢀtransientꢀresponseꢀofꢀLV
ꢀ
OUT
OUT
functionꢀofꢀC ꢀandꢀtheꢀloadꢀcurrent.ꢀWaveformsꢀgivenꢀ
dueꢀtoꢀthisꢀtransitionꢀisꢀaꢀfunctionꢀofꢀC ꢀandꢀtheꢀloadꢀ
OUT
OUT
inꢀtheꢀTypicalꢀPerformanceꢀCharacteristicsꢀsectionꢀshowꢀ
current.ꢀ Waveformsꢀ givenꢀ inꢀ theꢀ Typicalꢀ Performanceꢀ
typicalꢀtransientꢀresponsesꢀusingꢀtheꢀminimumꢀC ꢀofꢀ
Characteristicsꢀsectionꢀshowꢀtypicalꢀtransientꢀresponsesꢀ
OUT
2.2µFꢀandꢀloadꢀcurrentsꢀofꢀ1mAꢀandꢀ30mAꢀrespectively.ꢀ
usingꢀtheꢀminimumꢀC ꢀofꢀ2.2µFꢀandꢀloadꢀcurrentsꢀofꢀ
OUT
Generally,ꢀ theꢀ amplitudeꢀ ofꢀ anyꢀ transientsꢀ presentꢀ willꢀ
1mAꢀandꢀ30mAꢀrespectively.ꢀGenerally,ꢀtheꢀamplitudeꢀofꢀ
decreaseꢀasꢀC ꢀisꢀincreased.ꢀToꢀensureꢀreliableꢀoperationꢀ
anyꢀtransientsꢀpresentꢀwillꢀdecreaseꢀasꢀC ꢀisꢀincreased.ꢀ
OUT
OUT
andꢀadherenceꢀtoꢀtheꢀloadꢀregulationꢀlimitsꢀpresentedꢀinꢀ
Toꢀensureꢀreliableꢀoperationꢀandꢀadherenceꢀtoꢀtheꢀloadꢀ
regulationꢀlimitsꢀpresentedꢀinꢀtheꢀElectricalꢀCharactersticsꢀ
table,ꢀtheꢀloadꢀcurrentꢀmustꢀnotꢀexceedꢀtheꢀlinearꢀregulatorꢀ
theꢀElectricalꢀCharactersticsꢀtable,ꢀtheꢀloadꢀcurrentꢀmustꢀ
notꢀexceedꢀtheꢀlinearꢀregulatorꢀI ꢀlimitꢀofꢀ30mAꢀwithinꢀ
OUT
20msꢀafterꢀENBUCKꢀhasꢀtransitionedꢀtoꢀaꢀlogicꢀhigh.ꢀTheꢀ
I
ꢀlimitꢀofꢀ30mAꢀ1msꢀpriorꢀtoꢀENBUCKꢀtransitioningꢀtoꢀ
OUT
300mAꢀ I ꢀ limitꢀ ofꢀ VLDOꢀ appliesꢀ thereafter.ꢀ Further,ꢀ
aꢀlogicꢀlowꢀandꢀthereafer.ꢀFurther,ꢀforꢀconfigurationsꢀthatꢀ
doꢀnotꢀuseꢀtheꢀLTC3541-2’sꢀbuckꢀregulatorꢀtoꢀprovideꢀtheꢀ
OUT
forꢀconfigurationsꢀthatꢀdoꢀnotꢀuseꢀtheꢀLTC3541-2’sꢀbuckꢀ
regulatorꢀtoꢀprovideꢀtheꢀVLDOꢀinputꢀvoltageꢀ(LV ),ꢀtheꢀuserꢀ
VLDOꢀinputꢀvoltageꢀ(LV ),ꢀtheꢀuserꢀmustꢀcontinueꢀtoꢀensureꢀ
IN
IN
mustꢀensureꢀaꢀstableꢀLV ꢀvoltageꢀisꢀpresentꢀnoꢀlessꢀthanꢀ
aꢀstableꢀLV ꢀvoltageꢀnoꢀlessꢀthanꢀ1msꢀafterꢀENBUCKꢀhasꢀ
IN
IN
1msꢀpriorꢀtoꢀENBUCKꢀtransitioningꢀtoꢀaꢀlogicꢀhigh.
transitionedꢀtoꢀaꢀlogicꢀlow.
35412fb
ꢀꢀ
LTC3541-2
U U
W U
APPLICATIO S I FOR ATIO
TheꢀbasicꢀLTC3541-2ꢀapplicationꢀcircuitꢀisꢀshownꢀonꢀtheꢀ
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 ꢀandꢀtheꢀselectionꢀofꢀtheꢀoutputꢀ
IN OUT
1.65ꢀ
1.3ꢀ
1.1
capacitorꢀforꢀtheꢀVLDOꢀandꢀlinearꢀregulator.ꢀ
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
BUCK REGULATOR
Inductor Selection
CMD4D06
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
inductorsꢀproduceꢀhigherꢀrippleꢀcurrent.ꢀHigherꢀV ꢀorꢀV
ꢀ
OUT
IN
OUT
mayꢀalsoꢀincreaseꢀtheꢀrippleꢀcurrentꢀasꢀshownꢀinꢀEquationꢀ
Inꢀcontinuousꢀmode,ꢀtheꢀsourceꢀcurrentꢀofꢀtheꢀtopꢀMOSFETꢀ
isꢀaꢀsquareꢀwaveꢀofꢀdutyꢀcycleꢀV /V .ꢀToꢀpreventꢀlargeꢀ
voltageꢀtransients,ꢀaꢀlowꢀESRꢀinputꢀcapacitorꢀsizedꢀforꢀtheꢀ
maximumꢀRMSꢀcurrentꢀmustꢀbeꢀused.ꢀTheꢀmaximumꢀRMSꢀ
capacitorꢀcurrentꢀisꢀgivenꢀby:
1.ꢀAꢀreasonableꢀstartingꢀpointꢀforꢀsettingꢀrippleꢀcurrentꢀisꢀ
OUT IN
ΔI ꢀ=ꢀ200mAꢀ(40%ꢀofꢀ500mA).
L
VOUT
VIN
1
ΔIL =
VOUT 1−
(1)
f L
ꢀ
ꢀ
1/2
VOUT V − V
(
)
IN
OUT
TheꢀDCꢀcurrentꢀratingꢀofꢀtheꢀinductorꢀshouldꢀbeꢀatꢀleastꢀ
equalꢀtoꢀtheꢀmaximumꢀloadꢀcurrentꢀplusꢀhalfꢀtheꢀrippleꢀ
currentꢀtoꢀpreventꢀcoreꢀsaturation.ꢀThus,ꢀaꢀ600mAꢀratedꢀ
inductorꢀshouldꢀbeꢀenoughꢀforꢀmostꢀapplicationsꢀ(500mAꢀ
+ꢀ100mA).ꢀForꢀbetterꢀefficiency,ꢀchooseꢀaꢀlowꢀDCꢀresis-
tanceꢀinductor.
cIN required IRMS ≅IOMAX
VIN
ꢀ
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
ratherꢀthanꢀwhatꢀtheꢀLTC3541-2ꢀrequiresꢀtoꢀoperate.ꢀTableꢀ2ꢀ
showsꢀsomeꢀtypicalꢀsurfaceꢀmountꢀinductorsꢀthatꢀworkꢀ
wellꢀinꢀLTC3541-2ꢀapplications.
TheꢀselectionꢀofꢀC ꢀforꢀtheꢀbuckꢀregulatorꢀisꢀdrivenꢀbyꢀ
OUT
theꢀdesiredꢀbuckꢀloopꢀtransientꢀresponse,ꢀrequiredꢀeffectiveꢀ
seriesꢀresistanceꢀ(ESR)ꢀandꢀburstꢀrippleꢀperformance.
TheꢀLTC3541-2ꢀminimizesꢀtheꢀrequiredꢀnumberꢀofꢀexternalꢀ
componentsꢀbyꢀprovidingꢀinternalꢀloopꢀcompensationꢀforꢀ
theꢀbuckꢀregulatorꢀloop.ꢀLoopꢀstability,ꢀtransientꢀresponseꢀ
andꢀburstꢀrippleꢀperformanceꢀcanꢀbeꢀtailoredꢀbyꢀchoiceꢀ
ofꢀoutputꢀcapacitance.ꢀForꢀmanyꢀapplications,ꢀdesirableꢀ
35412fb
ꢀꢁ
LTC3541-2
U U
W U
APPLICATIO S I FOR ATIO
stability,ꢀtransientꢀresponseꢀandꢀrippleꢀperformanceꢀcanꢀ
beꢀ obtainedꢀ byꢀ choosingꢀ anꢀ outputꢀ capacitorꢀ valueꢀ ofꢀ
10µFꢀtoꢀ22µF.ꢀ
Whenꢀchoosingꢀtheꢀinputꢀandꢀoutputꢀceramicꢀcapacitors,ꢀ
chooseꢀtheꢀX5RꢀorꢀX7Rꢀdielectricꢀformulations.ꢀTheseꢀ
dielectricsꢀhaveꢀtheꢀbestꢀtemperatureꢀandꢀvoltageꢀcharac-
teristicsꢀofꢀallꢀtheꢀceramicsꢀforꢀaꢀgivenꢀvalueꢀandꢀsize.
Typically,ꢀonceꢀtheꢀESRꢀrequirementꢀforꢀC ꢀhasꢀbeenꢀ
OUT
met,ꢀtheꢀRMSꢀcurrentꢀratingꢀgenerallyꢀfarꢀexceedsꢀtheꢀ
Checking Transient Response
I
ꢀ requirement.ꢀ Theꢀ outputꢀ rippleꢀ ΔV ꢀ isꢀ
RIPPLE(P-P)
determinedꢀby:
OUT
Theꢀregulatorꢀloopꢀresponseꢀcanꢀbeꢀcheckedꢀbyꢀlookingꢀ
atꢀtheꢀloadꢀtransientꢀresponse.ꢀSwitchingꢀregulatorsꢀtakeꢀ
severalꢀcyclesꢀtoꢀrespondꢀtoꢀaꢀstepꢀinꢀloadꢀcurrent.ꢀWhenꢀ
1
ΔVOUT ≅ ΔIL ESR+
8fc
OUT
aꢀloadꢀstepꢀoccurs,ꢀV ꢀimmediatelyꢀshiftsꢀbyꢀanꢀamountꢀ
OUT
ꢀ
equalꢀtoꢀ(ΔI
ꢀ•ꢀESR),ꢀwhereꢀESRꢀisꢀtheꢀeffectiveꢀseriesꢀ
LOAD
whereꢀfꢀ=ꢀoperatingꢀfrequency,ꢀC ꢀ=ꢀoutputꢀcapacitanceꢀ
OUT
resistanceꢀofꢀC .ꢀΔI
ꢀalsoꢀbeginsꢀtoꢀchargeꢀorꢀdis-
OUT
LOAD
andꢀΔI ꢀ=ꢀrippleꢀcurrentꢀinꢀtheꢀinductor.ꢀForꢀaꢀfixedꢀoutputꢀ
L
chargeꢀC ,ꢀwhichꢀgeneratesꢀaꢀfeedbackꢀerrorꢀsignal.ꢀTheꢀ
OUT
voltage,ꢀtheꢀoutputꢀrippleꢀisꢀhighestꢀatꢀmaximumꢀinputꢀ
regulatorꢀloopꢀthenꢀactsꢀtoꢀreturnꢀV ꢀtoꢀitsꢀsteady-stateꢀ
value.ꢀDuringꢀthisꢀrecoveryꢀtimeꢀV ꢀcanꢀbeꢀmonitoredꢀ
OUT
OUT
voltageꢀsinceꢀΔI ꢀincreasesꢀwithꢀinputꢀvoltage.
L
forꢀovershootꢀorꢀringingꢀthatꢀwouldꢀindicateꢀaꢀstabilityꢀ
problem.ꢀForꢀaꢀdetailedꢀexplanationꢀofꢀswitchingꢀcontrolꢀ
loopꢀtheoryꢀseeꢀApplicationꢀNoteꢀ76.
Aluminumꢀelectrolyticꢀandꢀdryꢀtantalumꢀcapacitorsꢀareꢀbothꢀ
availableꢀinꢀsurfaceꢀmountꢀconfigurations.ꢀInꢀtheꢀcaseꢀofꢀ
tantalum,ꢀitꢀisꢀcriticalꢀthatꢀtheꢀcapacitorsꢀareꢀsurgeꢀtestedꢀ
forꢀuseꢀinꢀswitchingꢀpowerꢀsupplies.ꢀAnꢀexcellentꢀchoiceꢀisꢀ
theꢀAVXꢀTPSꢀseriesꢀofꢀsurfaceꢀmountꢀtantalum.ꢀTheseꢀareꢀ
speciallyꢀconstructedꢀandꢀtestedꢀforꢀlowꢀESRꢀsoꢀtheyꢀgiveꢀ
theꢀlowestꢀESRꢀforꢀaꢀgivenꢀvolume.ꢀOtherꢀcapacitorꢀtypesꢀ
includeꢀSanyoꢀPOSCAP,ꢀKemetꢀT510ꢀandꢀT495ꢀseries,ꢀandꢀ
Spragueꢀ593Dꢀandꢀ595Dꢀseries.ꢀConsultꢀtheꢀmanufacturerꢀ
forꢀotherꢀspecificꢀrecommendations.
Aꢀsecond,ꢀmoreꢀsevereꢀtransientꢀisꢀcausedꢀbyꢀswitchingꢀ
inꢀloadsꢀwithꢀlargeꢀ(>1µF)ꢀsupplyꢀbypassꢀcapacitors.ꢀTheꢀ
dischargedꢀbypassꢀcapacitorsꢀareꢀeffectivelyꢀputꢀinꢀparal-
lelꢀwithꢀC ,ꢀcausingꢀaꢀrapidꢀdropꢀinꢀV .ꢀNoꢀregulatorꢀ
OUT
OUT
canꢀdeliverꢀenoughꢀcurrentꢀtoꢀpreventꢀthisꢀproblemꢀifꢀtheꢀ
loadꢀswitchꢀresistanceꢀisꢀlowꢀandꢀitꢀisꢀdrivenꢀquickly.ꢀTheꢀ
onlyꢀsolutionꢀisꢀtoꢀlimitꢀtheꢀriseꢀtimeꢀofꢀtheꢀswitchꢀdriveꢀ
soꢀ thatꢀ theꢀ loadꢀ riseꢀ timeꢀ isꢀ limitedꢀ toꢀ approximatelyꢀ
Using Ceramic Input and Output Capacitors
(25ꢀ•ꢀC
).ꢀThus,ꢀaꢀ10µFꢀcapacitorꢀchargingꢀtoꢀ3.3Vꢀ
LOAD
Highꢀvalue,ꢀlowꢀcostꢀceramicꢀcapacitorsꢀareꢀnowꢀbecomingꢀ
availableꢀinꢀsmallerꢀcaseꢀsizes.ꢀTheirꢀhighꢀrippleꢀcurrent,ꢀ
highꢀvoltageꢀrating,ꢀandꢀlowꢀESRꢀmakeꢀthemꢀidealꢀforꢀ
switchingꢀregulatorꢀapplications.ꢀSinceꢀtheꢀLTC3541-2’sꢀ
controlꢀloopꢀdoesꢀnotꢀdependꢀonꢀtheꢀoutputꢀcapacitor’sꢀESRꢀ
forꢀstableꢀoperation,ꢀceramicꢀcapacitorsꢀcanꢀbeꢀusedꢀfreelyꢀ
toꢀachieveꢀveryꢀlowꢀoutputꢀrippleꢀandꢀsmallꢀcircuitꢀsize.
wouldꢀrequireꢀaꢀ250µsꢀriseꢀtime,ꢀlimitingꢀtheꢀchargingꢀ
currentꢀtoꢀaboutꢀ130mA.
VLDO/LINEAR REGULATOR
Output Capacitance and Transient Response
TheꢀLTC3541-2ꢀisꢀdesignedꢀtoꢀbeꢀstableꢀwithꢀaꢀwideꢀrangeꢀ
ofꢀceramicꢀoutputꢀcapacitors.ꢀTheꢀESRꢀofꢀtheꢀoutputꢀcapaci-
torꢀaffectsꢀstability,ꢀmostꢀnotablyꢀwithꢀsmallꢀcapacitors.ꢀAꢀ
minimumꢀoutputꢀcapacitorꢀofꢀ2.2µFꢀwithꢀanꢀESRꢀofꢀ0.05Ωꢀ
orꢀlessꢀisꢀrecommendedꢀtoꢀensureꢀstability.ꢀTheꢀLTC3541-2ꢀ
VLDOꢀisꢀaꢀmicropowerꢀdeviceꢀandꢀoutputꢀtransientꢀresponseꢀ
willꢀbeꢀaꢀfunctionꢀofꢀoutputꢀcapacitance.ꢀLargerꢀvaluesꢀ
ofꢀoutputꢀcapacitanceꢀdecreaseꢀtheꢀpeakꢀdeviationsꢀandꢀ
provideꢀimprovedꢀtransientꢀresponseꢀforꢀlargerꢀloadꢀcurrentꢀ
However,ꢀcareꢀmustꢀbeꢀtakenꢀwhenꢀceramicꢀcapacitorsꢀ
areꢀusedꢀatꢀtheꢀinputꢀandꢀtheꢀoutput.ꢀWhenꢀaꢀceramicꢀ
capacitorꢀisꢀusedꢀatꢀtheꢀinputꢀandꢀtheꢀpowerꢀisꢀsuppliedꢀ
byꢀaꢀwallꢀadapterꢀthroughꢀlongꢀwires,ꢀaꢀloadꢀstepꢀatꢀtheꢀ
outputꢀcanꢀinduceꢀringingꢀatꢀtheꢀinput,ꢀV .ꢀAtꢀbest,ꢀthisꢀ
IN
ringingꢀcanꢀcoupleꢀtoꢀtheꢀoutputꢀandꢀbeꢀmistakenꢀasꢀloopꢀ
instability.ꢀAtꢀworst,ꢀaꢀsuddenꢀinrushꢀofꢀcurrentꢀthroughꢀ
theꢀlongꢀwiresꢀcanꢀpotentiallyꢀcauseꢀaꢀvoltageꢀspikeꢀatꢀV ,ꢀ
IN
largeꢀenoughꢀtoꢀdamageꢀtheꢀpart.
35412fb
ꢀꢂ
LTC3541-2
U U
W U
APPLICATIO S I FOR ATIO
changes.ꢀNoteꢀthatꢀbypassꢀcapacitorsꢀusedꢀtoꢀdecoupleꢀ
individualꢀcomponentsꢀpoweredꢀbyꢀtheꢀLTC3541-2ꢀwillꢀ
increaseꢀtheꢀeffectiveꢀoutputꢀcapacitorꢀvalue.ꢀHighꢀESRꢀ
tantalumꢀ andꢀ electrolyticꢀ capacitorsꢀ mayꢀ beꢀ used,ꢀ butꢀ
aꢀlowꢀESRꢀceramicꢀcapacitorꢀmustꢀbeꢀinꢀparallelꢀatꢀtheꢀ
output.ꢀThereꢀisꢀnoꢀminimumꢀESRꢀorꢀmaximumꢀcapacitorꢀ
sizeꢀrequirement.
andꢀY5Vꢀdielectricsꢀareꢀgoodꢀforꢀprovidingꢀhighꢀcapaci-
tancesꢀinꢀaꢀsmallꢀpackage,ꢀbutꢀexhibitꢀlargeꢀvoltageꢀandꢀ
temperatureꢀcoefficientsꢀasꢀshownꢀinꢀFiguresꢀ6ꢀandꢀ7.ꢀ
Whenꢀusedꢀwithꢀaꢀ2Vꢀregulator,ꢀaꢀ1µFꢀY5Vꢀcapacitorꢀcanꢀ
loseꢀasꢀmuchꢀasꢀ75%ꢀofꢀitsꢀinitialꢀcapacitanceꢀoverꢀtheꢀ
operatingꢀtemperatureꢀrange.ꢀTheꢀX5RꢀandꢀX7Rꢀdielectricsꢀ
resultꢀinꢀmoreꢀstableꢀcharacteristicsꢀandꢀareꢀusuallyꢀmoreꢀ
suitableꢀforꢀuseꢀasꢀtheꢀoutputꢀcapacitor.ꢀTheꢀX7Rꢀtypeꢀhasꢀ
betterꢀstabilityꢀacrossꢀtemperature,ꢀwhileꢀtheꢀX5Rꢀisꢀlessꢀ
expensiveꢀandꢀisꢀavailableꢀinꢀhigherꢀvalues.ꢀInꢀallꢀcases,ꢀ
theꢀoutputꢀcapacitanceꢀshouldꢀneverꢀdropꢀbelowꢀ1µFꢀorꢀ
instabilityꢀorꢀdegradedꢀperformanceꢀmayꢀoccur.
Extraꢀconsiderationꢀmustꢀbeꢀgivenꢀtoꢀtheꢀuseꢀofꢀceramicꢀ
capacitors.ꢀCeramicꢀcapacitorsꢀareꢀmanufacturedꢀwithꢀaꢀ
varietyꢀofꢀdielectrics,ꢀeachꢀwithꢀdifferentꢀbehaviorꢀacrossꢀ
temperatureꢀ andꢀ appliedꢀ voltage.ꢀ Theꢀ mostꢀ commonꢀ
dielectricsꢀusedꢀareꢀZ5U,ꢀY5V,ꢀX5RꢀandꢀX7R.ꢀTheꢀZ5Uꢀ
EFFICIENCY CONSIDERATIONS
20
BOTH cAPAcITORS ARE 1µF,
10V, 0603 cASE SIZE
0
Generally,ꢀtheꢀefficiencyꢀofꢀaꢀregulatorꢀisꢀequalꢀtoꢀtheꢀout-
putꢀpowerꢀdividedꢀbyꢀtheꢀinputꢀpowerꢀtimesꢀ100%.ꢀItꢀisꢀ
oftenꢀusefulꢀtoꢀanalyzeꢀindividualꢀlossꢀtermsꢀtoꢀdetermineꢀ
whichꢀtermsꢀareꢀlimitingꢀefficiencyꢀandꢀwhatꢀifꢀanyꢀchangeꢀ
wouldꢀyieldꢀtheꢀgreatestꢀimprovement.ꢀEfficiencyꢀcanꢀbeꢀ
expressedꢀas:
X5R
–20
–40
Y5V
–60
–80
ꢀ Efficiencyꢀ=ꢀ100%ꢀ–ꢀ(L1ꢀ+ꢀL2ꢀ+ꢀL3ꢀ+ꢀ...)
whereꢀL1,ꢀL2,ꢀetc.ꢀareꢀtheꢀindividualꢀlossꢀtermsꢀasꢀaꢀper-
centageꢀofꢀinputꢀpower.
–100
0
8
2
4
6
10
Dc BIAS VOLTAGE (V)
35412 F06
Althoughꢀallꢀdissipativeꢀelementsꢀinꢀtheꢀcircuitꢀproduceꢀ
losses,ꢀthreeꢀmainꢀsourcesꢀtypicallyꢀaccountꢀforꢀtheꢀmajor-
Figure 6. Change in Capacitor vs Bias Voltage
ityꢀofꢀtheꢀlossesꢀinꢀtheꢀLTC3541-2ꢀcircuits:ꢀV ꢀquiescentꢀ
IN
2
current,ꢀI Rꢀlosses,ꢀandꢀlossꢀacrossꢀVLDOꢀoutputꢀdevice.ꢀ
20
WhenꢀoperatingꢀwithꢀbothꢀtheꢀbuckꢀandꢀVLDOꢀregulatorꢀ
0
activeꢀ(ENBUCKꢀandꢀENVLDOꢀequalꢀtoꢀlogicꢀhigh),ꢀV ꢀ
IN
X5R
quiescentꢀcurrentꢀlossꢀandꢀlossꢀacrossꢀtheꢀVLDOꢀoutputꢀ
–20
deviceꢀdominateꢀtheꢀefficiencyꢀlossꢀatꢀlowꢀloadꢀcurrents,ꢀ
Y5V
2
whereasꢀtheꢀI RꢀlossꢀandꢀlossꢀacrossꢀtheꢀVLDOꢀoutputꢀ
–40
–60
deviceꢀdominateꢀtheꢀefficiencyꢀlossꢀatꢀmediumꢀtoꢀhighꢀloadꢀ
currents.ꢀAtꢀlowꢀloadꢀcurrentsꢀwithꢀtheꢀpartꢀoperatingꢀwithꢀ
theꢀlinearꢀregulatorꢀ(ENBUCKꢀequalꢀtoꢀlogicꢀlow,ꢀENVLDOꢀ
equalꢀtoꢀlogicꢀhigh),ꢀefficiencyꢀisꢀtypicallyꢀdominatedꢀbyꢀ
–80
BOTH cAPAcITORS ARE 1µF,
10V, 0603 cASE SIZE
–100
theꢀlossꢀacrossꢀtheꢀlinearꢀregulatorꢀoutputꢀdeviceꢀandꢀV ꢀ
IN
–50
0
25
50
75
–25
TEMPERATURE (°c)
quiescentꢀcurrent.ꢀInꢀaꢀtypicalꢀefficiencyꢀplot,ꢀtheꢀefficiencyꢀ
curveꢀatꢀveryꢀlowꢀloadꢀcurrentsꢀcanꢀbeꢀmisleadingꢀsinceꢀ
theꢀactualꢀpowerꢀlostꢀisꢀofꢀlittleꢀconsequence.
35412 F07
Figure 7. Change in Capacitor vs Temperature
35412fb
ꢀꢃ
LTC3541-2
U U
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APPLICATIO S I FOR ATIO
1.ꢀTheꢀV ꢀquiescentꢀcurrentꢀlossꢀinꢀtheꢀbuckꢀisꢀdueꢀtoꢀtwoꢀ
THERMAL CONSIDERATIONS
IN
components:ꢀtheꢀDCꢀbiasꢀcurrentꢀasꢀgivenꢀinꢀtheꢀElectricalꢀ
Characteristicsꢀandꢀtheꢀinternalꢀmainꢀswitchꢀandꢀsynchro-
nousꢀswitchꢀgateꢀchargeꢀcurrents.ꢀTheꢀgateꢀchargeꢀcurrentꢀ
resultsꢀfromꢀswitchingꢀtheꢀgateꢀcapacitanceꢀofꢀtheꢀinternalꢀ
powerꢀswitches.ꢀEachꢀtimeꢀtheꢀgateꢀisꢀswitchedꢀfromꢀhighꢀ
toꢀlowꢀtoꢀhighꢀagain,ꢀaꢀpacketꢀofꢀcharge,ꢀdQ,ꢀmovesꢀfromꢀ
Theꢀ LTC3541-2ꢀ requiresꢀ theꢀ packageꢀ backplaneꢀ metalꢀ
(GNDꢀpin)ꢀtoꢀbeꢀwellꢀsolderedꢀtoꢀtheꢀPCꢀboard.ꢀThisꢀgivesꢀ
theꢀ DFNꢀ packageꢀ exceptionalꢀ thermalꢀ properties.ꢀ Theꢀ
powerꢀhandlingꢀcapabilityꢀofꢀtheꢀdeviceꢀwillꢀbeꢀlimitedꢀ
byꢀtheꢀmaximumꢀratedꢀjunctionꢀtemperatureꢀofꢀ125°C.ꢀ
TheꢀLTC3541-2ꢀhasꢀinternalꢀthermalꢀlimitingꢀdesignedꢀtoꢀ
protectꢀtheꢀdeviceꢀduringꢀmomentaryꢀoverloadꢀconditions.ꢀ
Forꢀcontinuousꢀnormalꢀconditions,ꢀtheꢀmaximumꢀjunctionꢀ
temperatureꢀratingꢀofꢀ125°Cꢀmustꢀnotꢀbeꢀexceeded.ꢀItꢀisꢀ
importantꢀtoꢀgiveꢀcarefulꢀconsiderationꢀtoꢀallꢀsourcesꢀofꢀ
thermalꢀresistanceꢀfromꢀjunctionꢀtoꢀambient.ꢀAdditionalꢀ
heatꢀsourcesꢀmountedꢀnearbyꢀmustꢀalsoꢀbeꢀconsidered.ꢀ
Forꢀsurfaceꢀmountꢀdevices,ꢀheatꢀsinkingꢀisꢀaccomplishedꢀ
byꢀusingꢀtheꢀheat-spreadingꢀcapabilitiesꢀofꢀtheꢀPCꢀboardꢀ
andꢀitsꢀcopperꢀtraces.ꢀCopperꢀboardꢀstiffenersꢀandꢀplatedꢀ
throughꢀholesꢀcanꢀalsoꢀbeꢀusedꢀtoꢀspreadꢀtheꢀheatꢀgener-
atedꢀbyꢀpowerꢀdevices.
V ꢀtoꢀground.ꢀTheꢀresultingꢀdQ/dtꢀisꢀtheꢀcurrentꢀoutꢀofꢀ
IN
V ꢀthatꢀisꢀtypicallyꢀlargerꢀthanꢀtheꢀDCꢀbiasꢀcurrentꢀandꢀ
IN
proportionalꢀtoꢀfrequency.ꢀBothꢀtheꢀDCꢀbiasꢀandꢀgateꢀchargeꢀ
lossesꢀareꢀproportionalꢀtoꢀV ꢀandꢀthusꢀtheirꢀeffectsꢀwillꢀ
IN
beꢀmoreꢀpronouncedꢀatꢀhigherꢀsupplyꢀvoltages.
2
2.ꢀI Rꢀlossesꢀareꢀcalculatedꢀfromꢀtheꢀresistancesꢀofꢀtheꢀ
internalꢀswitches,ꢀR ,ꢀandꢀexternalꢀinductorꢀR .ꢀInꢀcon-
SW
L
tinuousꢀmode,ꢀtheꢀaverageꢀoutputꢀcurrentꢀflowingꢀthroughꢀ
inductorꢀLꢀisꢀ“chopped”ꢀbetweenꢀtheꢀmainꢀswitchꢀandꢀtheꢀ
synchronousꢀswitch.ꢀThus,ꢀtheꢀseriesꢀresistanceꢀlookingꢀ
intoꢀtheꢀSWꢀpinꢀisꢀaꢀfunctionꢀofꢀbothꢀtopꢀandꢀbottomꢀ
MOSFETꢀR ꢀandꢀtheꢀdutyꢀcycleꢀ(DC)ꢀasꢀfollows:
DS(ON)
ToꢀavoidꢀtheꢀLTC3541-2ꢀexceedingꢀtheꢀmaximumꢀjunctionꢀ
temperature,ꢀsomeꢀthermalꢀanalysisꢀisꢀrequired.ꢀTheꢀgoalꢀ
ofꢀtheꢀthermalꢀanalysisꢀisꢀtoꢀdetermineꢀwhetherꢀtheꢀpowerꢀ
dissipatedꢀexceedsꢀtheꢀmaximumꢀjunctionꢀtemperatureꢀofꢀ
theꢀpart.ꢀTheꢀtemperatureꢀriseꢀisꢀgivenꢀby:
ꢀ R ꢀ=ꢀ(R
)(DC)ꢀ+ꢀ(R )(1ꢀ–ꢀDC)
DS(ON)TOP DS(ON)BOT
SW
TheꢀR
ꢀforꢀbothꢀtheꢀtopꢀandꢀbottomꢀMOSFETsꢀcanꢀ
DS(ON)
beꢀobtainedꢀfromꢀtheꢀTypicalꢀPerformanceꢀCharacteristicsꢀ
2
curves.ꢀThus,ꢀtoꢀobtainꢀI Rꢀlosses,ꢀsimplyꢀaddꢀR ꢀtoꢀ
SW
R ꢀandꢀmultiplyꢀtheꢀresultꢀbyꢀtheꢀsquareꢀofꢀtheꢀaverageꢀ
ꢀ T ꢀ=ꢀP •ꢀθ
L
R
Dꢀ JA
outputꢀcurrent.
whereꢀP ꢀisꢀtheꢀpowerꢀdissipatedꢀbyꢀtheꢀregulatorꢀandꢀθ ꢀ
D
JA
3.ꢀLossesꢀinꢀtheꢀVLDO/linearꢀregulatorꢀareꢀdueꢀtoꢀtheꢀDCꢀbiasꢀ
currentsꢀasꢀgivenꢀinꢀtheꢀElectricalꢀCharacteristicsꢀandꢀtoꢀtheꢀ
isꢀtheꢀthermalꢀresistanceꢀfromꢀtheꢀjunctionꢀofꢀtheꢀdieꢀtoꢀ
theꢀambientꢀtemperature.
(V ꢀ–ꢀV )ꢀvoltageꢀdropꢀacrossꢀtheꢀinternalꢀoutputꢀdeviceꢀ
IN
OUT
Theꢀjunctionꢀtemperature,ꢀT ,ꢀisꢀgivenꢀby:
J
transistor.
ꢀ T ꢀ=ꢀT ꢀ+ꢀT
R
J
A
Otherꢀ lossesꢀ whenꢀ theꢀ buckꢀ andꢀ VLDOꢀ regulatorꢀ areꢀ
inꢀoperationꢀ(ENBUCKꢀandꢀ ENVLDOꢀequalꢀlogicꢀhigh),ꢀ
whereꢀT ꢀisꢀtheꢀambientꢀtemperature.
A
includingꢀC ꢀandꢀC ꢀESRꢀdissipativeꢀlossesꢀandꢀinduc-
IN
OUT
torꢀcoreꢀlosses,ꢀgenerallyꢀaccountꢀforꢀlessꢀthanꢀ2%ꢀtotalꢀ
additionalꢀloss.
35412fb
ꢀꢄ
LTC3541-2
U U
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APPLICATIO S I FOR ATIO
Asꢀanꢀexample,ꢀconsiderꢀtheꢀLTC3541-2ꢀwithꢀanꢀinputꢀ DESIGN EXAMPLE
voltageꢀV ꢀofꢀ2.9V,ꢀanꢀLV ꢀvoltageꢀofꢀ1.875V,ꢀanꢀLV ꢀ
IN
IN
OUT
Asꢀaꢀdesignꢀexample,ꢀassumeꢀtheꢀLTC3541-2ꢀisꢀusedꢀinꢀ
aꢀsingleꢀlithium-ionꢀbatteryꢀpoweredꢀcellularꢀphoneꢀap-
voltageꢀofꢀ1.5V,ꢀaꢀloadꢀcurrentꢀofꢀ300mAꢀforꢀtheꢀVLDOꢀ
regulator,ꢀaꢀloadꢀcurrentꢀofꢀ200mAꢀforꢀtheꢀbuckꢀ(totalꢀ
loadꢀforꢀbuckꢀ=ꢀ500mA),ꢀandꢀanꢀambientꢀtemperatureꢀ
ofꢀ85°C.ꢀFromꢀtheꢀtypicalꢀperformanceꢀgraphꢀofꢀswitchꢀ
plication.ꢀTheꢀV ꢀwillꢀbeꢀoperatingꢀfromꢀaꢀmaximumꢀofꢀ
IN
4.2Vꢀdownꢀtoꢀaboutꢀ2.9V.ꢀTheꢀloadꢀcurrentꢀrequirementꢀ
isꢀaꢀmaximumꢀofꢀ0.5Aꢀforꢀtheꢀbuckꢀoutputꢀbutꢀmostꢀofꢀ
theꢀtimeꢀitꢀwillꢀbeꢀinꢀstandbyꢀmode,ꢀrequiringꢀonlyꢀ2mA.ꢀ
Efficiencyꢀatꢀbothꢀlowꢀandꢀhighꢀloadꢀcurrentsꢀisꢀimportant.ꢀ
Theꢀoutputꢀvoltageꢀforꢀtheꢀbuckꢀisꢀ1.875V.ꢀTheꢀrequire-
mentꢀforꢀtheꢀoutputꢀofꢀtheꢀVLDOꢀregulatorꢀisꢀ1.5Vꢀoutputꢀ
voltageꢀwhileꢀprovidingꢀupꢀtoꢀ0.3Aꢀofꢀcurrent.ꢀWithꢀthisꢀ
informationꢀweꢀcanꢀcalculateꢀLꢀusingꢀEquationꢀ2:
resistance,ꢀtheꢀR
ꢀofꢀtheꢀP-channelꢀswitchꢀatꢀ85°Cꢀisꢀ
DS(ON)
approximatelyꢀ0.25Ω.TheꢀR
ꢀofꢀtheꢀN-channelꢀswitchꢀ
DS(ON)
isꢀapproximatelyꢀ0.4Ω.ꢀTherefore,ꢀpowerꢀdissipatedꢀbyꢀtheꢀ
partꢀisꢀapproximately:
2
ꢀ P ꢀ=ꢀ(I
) ꢀ•ꢀR ꢀ+ꢀ(I
)•ꢀ
D
LOADBUCK
SW
LOADVLDO ꢀ
ꢀ ꢀ ꢀꢀꢀꢀꢀ(LV ꢀ–ꢀLV )ꢀ=ꢀ188mW
IN
OUT
VOUT
VIN
1
f ΔI
Forꢀtheꢀ3mmꢀ×ꢀ3mmꢀDFNꢀpackage,ꢀtheꢀθ ꢀisꢀ43°C/W.
JA
L =
VOUT 1−
(2)
L
Thus,ꢀtheꢀjunctionꢀtemperatureꢀofꢀtheꢀregulatorꢀis:
ꢀ
ꢀ
ꢀ T ꢀ=ꢀ85°Cꢀ+ꢀ(0.188)(43)ꢀ=ꢀ93°C
SubstitutingꢀV ꢀ=ꢀ1.875V,ꢀV ꢀ=ꢀ3.55Vꢀ(typ),ꢀΔI ꢀ=ꢀ200mAꢀ
J
OUT
IN
L
andꢀfꢀ=ꢀ2.25MHzꢀinꢀEquationꢀ3ꢀgives:
whichꢀisꢀwellꢀbelowꢀtheꢀmaximumꢀjunctionꢀtemperatureꢀ
ofꢀ125°C.
1.8V
2.25MHz(200mA)
1.8V
3.45V
L =
1−
=1.91µH
(3)
Noteꢀthatꢀatꢀhigherꢀsupplyꢀvoltages,ꢀtheꢀjunctionꢀtempera-
tureꢀisꢀlowerꢀdueꢀtoꢀreducedꢀswitchꢀresistanceꢀR
ꢀ
ꢀ
.
DS(ON)
Aꢀ2.2µHꢀinductorꢀworksꢀwellꢀforꢀthisꢀapplication.ꢀForꢀbestꢀ
efficiencyꢀchooseꢀaꢀ600mAꢀorꢀgreaterꢀinductorꢀwithꢀlessꢀ
thanꢀ0.2Ωꢀseriesꢀresistance.
PC BOARD LAYOUT CHECKLIST
Whenꢀlayingꢀoutꢀtheꢀprintedꢀcircuitꢀboard,ꢀtheꢀfollowingꢀ
checklistꢀshouldꢀbeꢀusedꢀtoꢀensureꢀproperꢀoperationꢀofꢀtheꢀ
LTC3541-2.ꢀCheckꢀtheꢀfollowingꢀinꢀyourꢀlayout:
C ꢀwillꢀrequireꢀanꢀRMSꢀcurrentꢀratingꢀofꢀatꢀleastꢀ0.25Aꢀ
IN
=ꢀ I
/2ꢀ atꢀ temperatureꢀ .ꢀ C ꢀ forꢀ theꢀ buckꢀ isꢀ
LOAD(MAX)
OUT
chosenꢀtoꢀhaveꢀaꢀvalueꢀofꢀ22µFꢀandꢀanꢀESRꢀofꢀlessꢀthanꢀ
0.25Ω.ꢀInꢀmostꢀcases,ꢀaꢀceramicꢀcapacitorꢀwillꢀsatisfyꢀ
thisꢀrequirement.
1.ꢀTheꢀpowerꢀtraces,ꢀconsistingꢀofꢀtheꢀGNDꢀtrace,ꢀtheꢀSWꢀ
traceꢀandꢀtheꢀV ꢀtraceꢀshouldꢀbeꢀkeptꢀshort,ꢀdirectꢀandꢀ
IN
wide.
C
ꢀforꢀtheꢀVLDOꢀregulatorꢀisꢀchosenꢀasꢀ2.2µF.
OUT
2.ꢀDoesꢀtheꢀ(+)ꢀplateꢀofꢀC ꢀconnectꢀtoꢀV ꢀasꢀcloselyꢀasꢀ
IN
IN
possible?ꢀThisꢀcapacitorꢀprovidesꢀtheꢀACꢀcurrentꢀtoꢀtheꢀ
internalꢀpowerꢀMOSFETs.
3.ꢀKeepꢀtheꢀswitchingꢀnode,ꢀSW,ꢀawayꢀfromꢀtheꢀsensitiveꢀ
LFBꢀnode.
4.ꢀ Keepꢀ theꢀ (–)ꢀ platesꢀ ofꢀ C ꢀ andꢀ C ꢀ asꢀ closeꢀ asꢀ
IN
OUT
possible.
35412fb
ꢀꢅ
LTC3541-2
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
2.9V TO 4.2V
V
OUT
1V/DIV
SW
ENVLDO
MODE
V
IN
2.2µH
LV
OUT
LTC3541-2
ENBUCK GND
1V/DIV
V
V
OUT
OUT1
V
IN
V
1.875V
200mA
OUT2
2V/DIV
1.5V
LV
LV
OUT
PGND
IN
300mA
10µF
2.2µF
35412TA02b
35412 TA02a
I
I
= 200mA
LVOUT
2ms/DIV
VOUT
= 300mA
Dual Output with Minimal External Components Using Auto-Start-Up
Sequence, Buck in Pulse-Skip Mode for Low Noise Operation
V
IN
2.9V TO 4.2V
V
OUT
1V/DIV
SW
ENVLDO
MODE
V
IN
2.2µH
LV
OUT
LTC3541-2
1V/DIV
ENBUCK
GND
V
V
OUT1
OUT
V
IN
1.875V
200mA
V
OUT2
2V/DIV
1.5V
LV
LV
OUT
PGND
IN
300mA
10µF
2.2µF
35412TA03b
35412 TA03a
I
I
= 200mA
LVOUT
2ms/DIV
VOUT
= 300mA
35412fb
ꢀꢆ
LTC3541-2
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
2.9V TO 4.2V
V
OUT
1V/DIV
SW
ENVLDO
MODE
V
IN
2.2µH
LV
LTC3541-2
OUT
1V/DIV
ENBUCK
GND
V
V
OUT1
OUT
V
IN
1.875V
200mA
V
OUT2
2V/DIV
1.5V
LV
LV
OUT
PGND
IN
300mA
10µF
2.2µF
35412 TA04a
35412TA04b
I
I
= 200mA
LVOUT
4ms/DIV
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
2.9V TO 4.2V
V
OUT
1V/DIV
SW
ENVLDO
MODE
V
LV
IN
OUT
2.2µH
1V/DIV
LTC3541-2
ENBUCK GND
V
IN
2V/DIV
V
V
OUT1
OUT
1.875V
200mA
V
OUT2
LV
LV
PGND
1.5V
IN
OUT
300mA
2.2µF
10µF
35412TA05b
I
I
= 200mA
LVOUT
4ms/DIV
VOUT
35412 TA05a
= 30mA
35412fb
ꢀꢇ
LTC3541-2
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
35412fb
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
LTC3541-2
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
V :ꢀ1.8Vꢀtoꢀ20V,ꢀV
LT®3023ꢀ
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,ꢀꢀ
IN
DO
OUT(MIN)
ꢀ=ꢀ45mV,ꢀI ꢀ=ꢀ50µA,ꢀI ꢀ<ꢀ1µA,ꢀV ꢀ=ꢀADJ,ꢀDFNꢀPackages,ꢀStableꢀwithꢀ
Q SD OUT
V
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.ꢀ
35412fb
LT 0407 REV A • 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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