LTC3541EDD-1-PBF [Linear]
High Efficiency Buck + VLDO Regulator; 高效率降压+ VLDO稳压器
| 型号： | LTC3541EDD-1-PBF |
| 厂家： | 
Linear |
| 描述： | High Efficiency Buck + VLDO Regulator |
| 文件： | 总20页 (文件大小：356K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LTC3541-1
High Efficiency
Buck + VLDO Regulator
U
DESCRIPTIO
FEATURES
ꢀ High Efficiency, 500mA Buck Plus 300mA VLDO
Regulator
TM
TheꢀLTC®3541-1ꢀcombinesꢀaꢀsynchronousꢀbuckꢀDC/
DCꢀconverterꢀwithꢀaꢀveryꢀlowꢀdropoutꢀlinearꢀregulatorꢀ
(VLDO)ꢀtoꢀprovideꢀupꢀtoꢀtwoꢀoutputꢀvoltagesꢀfromꢀaꢀsingleꢀ
inputꢀvoltageꢀwithꢀminimalꢀexternalꢀcomponents.ꢀWhenꢀ
configuredꢀforꢀdualꢀoutputꢀoperation,ꢀtheꢀLTC3541-1’sꢀautoꢀ
start-upꢀfeatureꢀwillꢀbringꢀtheꢀVLDO/linearꢀregulatorꢀoutputꢀ
intoꢀregulationꢀinꢀaꢀcontrolledꢀmannerꢀpriorꢀtoꢀenablingꢀtheꢀ
Buckꢀregulatorꢀoutputꢀwithoutꢀtheꢀneedꢀforꢀexternalꢀpinꢀ
control.ꢀBuckꢀoutputꢀpriorꢀtoꢀVLDO/linearꢀregulatorꢀoutputꢀ
sequencingꢀmayꢀalsoꢀbeꢀobtainedꢀviaꢀexternalꢀpinꢀcontrol.ꢀ
TheꢀinputꢀvoltageꢀrangeꢀisꢀideallyꢀsuitedꢀforꢀLi-Ionꢀbattery-
poweredꢀapplications,ꢀasꢀwellꢀasꢀpoweringꢀsub-3.3Vꢀlogicꢀ
fromꢀ5Vꢀorꢀ3.3Vꢀrails.
■
Auto Start-Up Powers VLDO/Linear Regulator
Output Prior to Buck Regulator Output
■
ꢀ Independent High Efficiency, 500mA Buck
(V : 2.7V to 5.5V)
IN
■
■
■
■
■
■
ꢀ 300mA VLDO Regulator with 30mA Standalone Mode
ꢀ No External Schottky Diodes Required
ꢀ Buck Output Voltage Range: 0.8V to 5V
ꢀ VLDO Input Voltage Range (LV ): 0.9V to 5.5V
IN
ꢀ VLDO Output Voltage Range VLDO: 0.4V to 4.1V
ꢀ SelectableꢀFixedꢀFrequency,ꢀPulse-SkipꢀOperationꢀor
ꢀ BurstꢀMode®ꢀOperation
■
ꢀ Short-CircuitꢀProtected
Theꢀsynchronousꢀbuckꢀconverterꢀprovidesꢀaꢀhighꢀefficiencyꢀ
output,ꢀtypicallyꢀ90%,ꢀcapableꢀofꢀprovidingꢀupꢀtoꢀ500mAꢀ
ofꢀcontinuousꢀoutputꢀcurrentꢀwhileꢀswitchingꢀatꢀ2.25MHz,ꢀ
allowingꢀtheꢀuseꢀofꢀsmallꢀsurfaceꢀmountꢀinductorsꢀandꢀca-
pacitors.ꢀAꢀmode-selectꢀpinꢀallowsꢀBurstꢀModeꢀoperationꢀ
toꢀbeꢀenabledꢀforꢀhigherꢀefficiencyꢀatꢀlightꢀloadꢀcurrents,ꢀorꢀ
disabledꢀforꢀlowerꢀnoise,ꢀconstantꢀfrequencyꢀoperation.ꢀ
■
ꢀ CurrentꢀModeꢀOperationꢀforꢀExcellentꢀLineꢀandꢀLoadꢀ
TransientꢀResponse
■
ꢀ ConstantꢀFrequencyꢀOperation:ꢀ2.25MHz
■
ꢀ LowꢀDropoutꢀBuckꢀOperation:ꢀ100%ꢀDutyꢀCycle
■
ꢀ Small,ꢀThermallyꢀEnhanced,ꢀ10-Leadꢀ(3mmꢀ×ꢀ3mm)ꢀ
DFNꢀPackage
U
APPLICATIO S
TheꢀVLDOꢀregulatorꢀprovidesꢀaꢀlowꢀnoise,ꢀlowꢀvoltageꢀ
outputꢀcapableꢀofꢀprovidingꢀupꢀtoꢀ300mAꢀofꢀcontinuousꢀ
outputꢀcurrentꢀusingꢀonlyꢀaꢀ2.2µFꢀceramicꢀcapacitor.ꢀTheꢀ
inputꢀsupplyꢀvoltageꢀofꢀtheꢀVLDOꢀregulatorꢀ(LV )ꢀmayꢀ
comeꢀfromꢀtheꢀbuckꢀregulatorꢀorꢀaꢀseparateꢀsupply.
■
ꢀ PDAs/PalmtopꢀPCs
■
ꢀ DigitalꢀCameras
IN
■
ꢀ CellularꢀPhones
ꢀ PCꢀCards
ꢀ WirelessꢀandꢀDSLꢀModems
ꢀ OtherꢀPortableꢀPowerꢀSystems
■
, LT, LTc, LTM and Burst Mode are registered trademarks of Linear Teꢀhnology
corporation. VLDO is a trademark of Linear Teꢀhnology corporation.
All other trademarks are the property of their respeꢀtive owners.
■
■
Proteꢀted by U.S. Patents, inꢀluding 5481178, 6611131, 6304066, 6498466, 6580258
U
Buck (Burst) Efficiency and Power Loss vs Load Current
TYPICAL APPLICATIO
100
1
LTC3541-1 Typical Application
90
EFFICIENCY
80
V
IN
2.9V TO 5.5V
0.1
70
V
ENVLDO
IN
60
50
POWER LOSS
ENBUCK MODE
LTC3541-1
0.01
0.001
0.0001
2.2µH
V
150k
412k
OUT1
2.5V
SW
GND
40
30
20
10
0
200mA
LV
LFB
IN
243k
22pF
BUCKFB LV
PGND
OUT
V
V
V
= 3.3V
OUT2
IN
OUT
1.5V
= 2.5V
115k
10µF
300mA
2.2µF
1
10
100
1000
35411 TA01b
LOAD CURRENT (mA)
35411 TA01a
35411fa
ꢀ
LTC3541-1
W W W U
ABSOLUTE AXI U RATI GS
pIN CONFIGURATION
(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
BUcKFB
LFB
9
8
7
6
ENVLDO
11
MODE
GND
PinꢀVoltages:
ꢀ ENVLDO,ꢀENBUCK,ꢀMODE,ꢀSW,ꢀ
LV
LV
IN
OUT
ꢀ LFB,ꢀBUCKFBꢀ.............................–0.3Vꢀtoꢀ(V ꢀ+ꢀ0.3V)
LinearꢀRegulatorꢀI
OperatingꢀAmbientꢀTemperatureꢀRangeꢀ
(Noteꢀ2).................................................... –40°Cꢀtoꢀ85°C
JunctionꢀTemperatureꢀ(Noteꢀ5)ꢀ............................. 125°C
StorageꢀTemperatureꢀRange................... –65°Cꢀtoꢀ125°C
IN
ꢀ(100ms)ꢀ(Noteꢀ9)ꢀ......100mA
OUT(MAX)
DD PAcKAGE
10-LEAD (3mm × 3mm) PLASTIc DFN
ꢀ=ꢀ125°C,ꢀθ ꢀ=ꢀ43°C/Wꢀ
JA
EXPOSEDꢀPADꢀ(PINꢀ11)ꢀISꢀGND,ꢀMUSTꢀBEꢀSOLDEREDꢀTOꢀPCB
ꢀ
T
JMAX
ORdeR INFORmATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
10-Leadꢀ(3mmꢀ×ꢀ3mm)ꢀPlasticꢀDFN
TEMPERATURE RANGE
–40°Cꢀtoꢀ85°C
LTC3541EDD-1#PBF
LTC3541EDD-1#TRPBF
LCWQ
ConsultꢀLTCꢀMarketingꢀforꢀpartsꢀspecifiedꢀwithꢀwiderꢀoperatingꢀtemperatureꢀranges.ꢀ
ConsultꢀLTCꢀMarketingꢀforꢀinformationꢀonꢀnon-standardꢀleadꢀbasedꢀfinishꢀparts.
*Forꢀmoreꢀinformationꢀonꢀleadꢀfreeꢀpartꢀmarking,ꢀgoꢀto:ꢀhttp://www.linear.com/leadfree/ꢀꢀ
Forꢀmoreꢀinformationꢀonꢀtapeꢀandꢀreelꢀspecifications,ꢀgoꢀto:ꢀhttp://www.linear.com/tapeandreel/
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)
MIN
0.8
TYP
0.95
MAX
1.25
UNITS
Aꢀ
I
I
I
PK
IN
●
●
●
●
BUCKFBꢀPinꢀInputꢀCurrent
LFBꢀPinꢀInputꢀCurrent
InputꢀVoltageꢀRange
V
V
ꢀ=ꢀ0.9V
BUCKFB
50
nA
nA
BUCKFB
LFB
ꢀ=ꢀ0.45V
LFB
–200
2.7
–40
V
V
(Noteꢀ4)
5.5
0.4
V
IN
BuckꢀV ꢀLineꢀRegulationꢀꢀ
V ꢀ=ꢀ2.7Vꢀtoꢀ5.5V,ꢀENBUCKꢀ=ꢀV ,ꢀꢀ
0.04
0.6
0.6
0.3
%/V
IN(LINEREG)
IN
IN
IN
ENVLDOꢀ=ꢀ0V,ꢀMODEꢀ=ꢀV ꢀ(Noteꢀ6)
IN
VLDOꢀV ꢀLineꢀRegulationꢀꢀ
V ꢀ=ꢀ2.7Vꢀtoꢀ5.5V,ꢀLV ꢀ=ꢀ1.2V,ꢀENBUCKꢀ=ꢀV ,ꢀ
mV/V
mV/V
mV/V
IN
IN
OUT
IN
(ReferredꢀtoꢀLFB)
ENVLDOꢀ=ꢀV ,ꢀI
ꢀ=ꢀ100mA,ꢀLV ꢀ=ꢀ1.5Vꢀ
IN OUT(VLDO) IN
LinearꢀRegulatorꢀV ꢀLineꢀ
Regulationꢀ(ReferredꢀtoꢀLFB)
V ꢀ=ꢀ2.7Vꢀtoꢀ5.5V,ꢀLV ꢀ=ꢀ1.2V,ꢀENBUCKꢀ=ꢀ0V,ꢀ
IN OUT
IN
ENVLDOꢀ=ꢀV ,ꢀI
ꢀ=ꢀ10mA
IN OUT(LREG)
LV
LV ꢀLineꢀRegulationꢀꢀ
LV ꢀ=ꢀ0.9Vꢀtoꢀ5.5V,ꢀV ꢀ=ꢀ5.5V,ꢀLV ꢀ=ꢀ0.4V,ꢀꢀ
IN(LINEREG)
IN
IN IN OUT
(ReferredꢀtoꢀLFB)
ENBUCKꢀ=ꢀV ,ꢀENVLDOꢀ=ꢀV ,ꢀMODEꢀ=ꢀV ,ꢀ
IN
IN
IN
I
ꢀ=ꢀ100mA
OUT(VLDO)
VLDO
LV ꢀ–ꢀLV ꢀDropoutꢀVoltageꢀ
LV ꢀ=ꢀ1.5V,ꢀENBUCKꢀ=ꢀV ,ꢀENVLDOꢀ=ꢀV ,ꢀꢀ
28
60
mV
DO
IN
OUT
IN
IN
IN
(Noteꢀ9)
MODEꢀ=ꢀV ,ꢀI
ꢀ=ꢀ50mA,ꢀV ꢀ=ꢀ0.3Vꢀ
IN OUT(VLDO) LFB
V
BuckꢀOutputꢀLoadꢀRegulationꢀ
ENBUCKꢀ=ꢀV ,ꢀENVLDOꢀ=ꢀ0V,ꢀMODEꢀ=ꢀV ꢀ(Noteꢀ6)
0.5
%
%
LOADREG
IN
IN
●
●
VLDOꢀOutputꢀLoadꢀRegulationꢀ
I
ꢀ=ꢀ1mAꢀ–ꢀ300mA,ꢀLV ꢀ=ꢀ1.5V,ꢀLV ꢀ=ꢀ1.2V,ꢀ
0.25
0.5
0.5
OUT(VLDO)
IN
OUT
ENBUCKꢀ=ꢀV ,ꢀENVLDOꢀ=ꢀV ,ꢀMODEꢀ=ꢀV
IN
IN
IN
LinearꢀRegulatorꢀOutputꢀLoadꢀ
I
ꢀ=ꢀ1mAꢀ–ꢀ30mA,ꢀLV ꢀ=ꢀ1.2V,ꢀꢀ
0.25
%
OUT(LREG)
OUT
ENBUCKꢀ=ꢀ0V,ꢀENVLDOꢀ=ꢀV
IN
35411fa
ꢁ
LTC3541-1
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
ReferenceꢀRegulationꢀVoltageꢀ
(Noteꢀ6)
CONDITIONS
ENBUCKꢀ=ꢀV ,ꢀENVLDOꢀ=ꢀ0V,ꢀT ꢀ=ꢀ25°C
MIN
0.784
TYP
0.8
MAX
0.816
UNITS
V
V
BUCKFB
IN
A
ENBUCKꢀ=ꢀV ,ꢀENVLDOꢀ=ꢀ0V,ꢀ0°Cꢀ≤ꢀT ꢀ≤ꢀ85°C
0.782
0.78
0.8
0.8
0.4
0.4
0.4
85
0.818
0.82
V
V
IN
A
●
●
ENBUCKꢀ=ꢀV ,ꢀENVLDOꢀ=ꢀ0V,ꢀ–40°Cꢀ≤ꢀT ꢀ≤ꢀ85°C
IN
A
V
ReferenceꢀRegulationꢀVoltageꢀ
(Noteꢀ7)
ENBUCKꢀ=ꢀ0V,ꢀENVLDOꢀ=ꢀV ,ꢀT ꢀ=ꢀ25°C
0.392
0.391
0.390
0.408
0.409
0.410
V
LFB
IN
A
ENBUCKꢀ=ꢀ0V,ꢀENVLDOꢀ=ꢀV ,ꢀ0°Cꢀ≤ꢀT ꢀ≤ꢀ85°C
V
IN
A
ENBUCKꢀ=ꢀ0V,ꢀENVLDOꢀ=ꢀV ,ꢀ–40°Cꢀ≤ꢀT ꢀ≤ꢀ85°C
V
IN
A
I
Buckꢀ+ꢀVLDOꢀꢀ
LV ꢀ=ꢀ1.5V,ꢀLV ꢀ=ꢀ1.2V,ꢀENBUCKꢀ=ꢀV ,ꢀꢀ
µA
S
IN
OUT
IN
BurstꢀModeꢀSleepꢀꢀ
ENVLDOꢀ=ꢀV ,ꢀMODEꢀ=ꢀ0V,ꢀI
ꢀ=ꢀ10µA,ꢀ
IN
OUT(VLDO)
V ꢀQuiescentꢀCurrent
V
ꢀ=ꢀ0.9V
BUCKFB
IN
Buckꢀ+ꢀVLDOꢀꢀ
LV ꢀ=ꢀ1.5V,ꢀLV ꢀ=ꢀ1.2V,ꢀENBUCKꢀ=ꢀV ,ꢀꢀ
315
300
55
µA
µA
µA
µA
µA
µA
IN
OUT
IN
BurstꢀModeꢀActiveꢀ
ENVLDOꢀ=ꢀV ,ꢀMODEꢀ=ꢀ0V,ꢀI
ꢀ=ꢀ10µA,ꢀ
IN
OUT(VLDO)
V ꢀQuiescentꢀCurrent
V
ꢀ=ꢀ0.7V
BUCKFB
IN
Buckꢀ+ꢀVLDOꢀ
LV ꢀ=ꢀ1.5V,ꢀLV ꢀ=ꢀ1.2V,ꢀENBUCKꢀ=ꢀV ,ꢀꢀ
IN
OUT
IN
Pulse-SkipꢀModeꢀActiveꢀ
ENVLDOꢀ=ꢀV ,ꢀMODEꢀ=ꢀV ,ꢀI
V
V
ꢀ=ꢀ10µA,ꢀ
IN
IN OUT(VLDO)
V ꢀQuiescentꢀCurrent
ꢀ=ꢀ0.7V
IN
BUCKFB
Buckꢀ
ꢀ=ꢀ0.9V,ꢀI
ꢀ=ꢀ0A,ꢀENBUCKꢀ=ꢀV ,ꢀ
BUCKFB
ENVLDOꢀ=ꢀ0V,ꢀMODEꢀ=ꢀ0V
OUT(BUCK) IN
BurstꢀModeꢀSleepꢀ
V ꢀQuiescentꢀCurrent
IN
Buckꢀ
V
ꢀ=ꢀ0.7V,ꢀI
ꢀ=ꢀ0A,ꢀENBUCKꢀ=ꢀV ,ꢀ
300
285
50
BUCKFB
OUT(BUCK)
IN
BurstꢀModeꢀActiveꢀ
ENVLDOꢀ=ꢀ0V,ꢀMODEꢀ=ꢀ0V
V ꢀQuiscentꢀCurrent
IN
Buckꢀ
V
BUCKFB
ꢀ=ꢀ0.7V,ꢀI ꢀ=ꢀ0A,ꢀENBUCKꢀ=ꢀV ,ꢀ
OUT(BUCK)
IN
Pulse-SkipꢀModeꢀActiveꢀ
ENVLDOꢀ=ꢀ0V,ꢀMODEꢀ=ꢀV
IN
V ꢀQuiescentꢀCurrent
IN
LinearꢀRegulatorꢀV ꢀQuiescentꢀ
Current
LV ꢀ=ꢀ1.2V,ꢀENBUCKꢀ=ꢀ0V,ꢀENVLDOꢀ=ꢀV ,ꢀ
OUT IN
IN
I
ꢀ=ꢀ10µA
OUT(LREG)
V ꢀShutdownꢀQuiescentꢀCurrent ENBUCKꢀ=ꢀ0V,ꢀENVLDOꢀ=ꢀ0V
2.5
0.1
µA
µA
MHz
Ω
IN
LV ꢀShutdownꢀQuiescentꢀCurrent LV ꢀ=ꢀ3.6V,ꢀENBUCKꢀ=ꢀ0V,ꢀENVLDOꢀ=ꢀ0V
IN
IN
●
f
OscillatorꢀFrequency
1.8
0.9
2.25
0.25
0.35
0.01
2.7
1
OSC
R
R
R
R
ꢀofꢀP-ChannelꢀMOSFET
ꢀofꢀN-ChannelꢀMOSFET
I
I
ꢀ=ꢀ100mA
PFET
NFET
LSW
DS(ON)
SW
Ω
ꢀ=ꢀ100mA
SW
DS(ON)
I
SWꢀLeakage
Enableꢀ=ꢀ0V,ꢀV ꢀ=ꢀ0Vꢀorꢀ6V,ꢀV ꢀ=ꢀ6V
µA
V
SW
IN
●
●
●
V
V
InputꢀPinꢀHighꢀThreshold
InputꢀPinꢀLowꢀThreshold
InputꢀPinꢀCurrent
MODE,ꢀENBUCK,ꢀENVLDO
IH
MODE,ꢀENBUCK,ꢀENVLDO
0.3
1
V
IL
I
I
I
,ꢀ
0.01
µA
MODE
,ꢀ
ENBUCK
ENVLDO
Note 4:ꢀMinimumꢀoperatingꢀV ꢀvoltageꢀrequiredꢀforꢀVLDOꢀregulatorꢀandꢀ
Note 1:ꢀStressesꢀbeyondꢀthoseꢀlistedꢀunderꢀAbsoluteꢀMaximumꢀRatingsꢀ
mayꢀcauseꢀpermanentꢀdamageꢀtoꢀtheꢀdevice.ꢀExposureꢀtoꢀanyꢀAbsoluteꢀ
MaximumꢀRatingꢀconditionꢀforꢀextendedꢀperiodsꢀmayꢀaffectꢀdeviceꢀ
reliabilityꢀandꢀlifetime.
Note 2:ꢀTheꢀLTC3541-1ꢀisꢀguaranteedꢀtoꢀmeetꢀperformanceꢀspecificationsꢀ
fromꢀ0°Cꢀtoꢀ85°C.ꢀVLDO/linearꢀregulatorꢀoutputꢀisꢀtestedꢀandꢀspecifiedꢀ
IN
linearꢀregulatorꢀregulationꢀis:ꢀꢀ
ꢀ
ꢀ
ꢀ
V ꢀ≥ꢀLV ꢀ+ꢀ1.4VꢀandꢀV ꢀ≥ꢀ2.7V
IN
OUT
IN
Note 5:ꢀT ꢀisꢀcalculatedꢀfromꢀtheꢀambientꢀtemperature,ꢀT ,ꢀandꢀpowerꢀ
J
A
dissipation,ꢀP ,ꢀaccordingꢀtoꢀtheꢀfollowingꢀformula:
D
ꢀ
T ꢀ=ꢀT ꢀ+ꢀ(P ꢀ•ꢀ43°C/W)
J A D
underꢀpulseꢀloadꢀconditionsꢀsuchꢀthatꢀT ꢀ≈ꢀT ,ꢀandꢀareꢀ100%ꢀproductionꢀ
J
A
Note 6:ꢀTheꢀLTC3541-1ꢀisꢀtestedꢀinꢀaꢀproprietaryꢀtestꢀmodeꢀthatꢀconnectsꢀ
ꢀtoꢀtheꢀoutputꢀofꢀtheꢀerrorꢀamplifier.ꢀForꢀtheꢀreferenceꢀregulationꢀ
testedꢀatꢀ25°C.ꢀSpecificationsꢀoverꢀtheꢀ–40°Cꢀtoꢀ85°Cꢀoperatingꢀ
temperatureꢀrangeꢀareꢀassuredꢀbyꢀdesign,ꢀcharacterizationꢀandꢀcorrelationꢀ
withꢀstatisticalꢀprocessꢀcontrols.
V
BUCKFB
andꢀlineꢀregulationꢀtests,ꢀtheꢀoutputꢀofꢀtheꢀerrorꢀamplifierꢀisꢀsetꢀtoꢀtheꢀ
midpoint.ꢀForꢀtheꢀloadꢀregulationꢀtest,ꢀtheꢀoutputꢀofꢀtheꢀerrorꢀamplifierꢀisꢀ
drivenꢀtoꢀminimumꢀandꢀmaximumꢀofꢀtheꢀsignalꢀrange.
Note 3:ꢀMinimumꢀoperatingꢀLV ꢀvoltageꢀrequiredꢀforꢀVLDOꢀregulatorꢀ
IN
regulationꢀis:ꢀ
ꢀ
LV ꢀ≥ꢀLV ꢀ+ꢀV
ꢀandꢀLV ꢀ≥ꢀ0.9V
DROPOUT IN
IN
OUT
35411fa
ꢂ
LTC3541-1
ELECTRICAL CHARACTERISTICS
Note 10:ꢀThisꢀICꢀincludesꢀovertemperatureꢀprotectionꢀthatꢀisꢀintendedꢀ
toꢀprotectꢀtheꢀdeviceꢀduringꢀmomentaryꢀoverloadꢀconditions.ꢀJunctionꢀ
temperatureꢀwillꢀexceedꢀ125°Cꢀwhenꢀovertemperatureꢀprotectionꢀisꢀactive.ꢀ
Continuousꢀoperationꢀaboveꢀtheꢀspecifiedꢀmaximumꢀoperatingꢀjunctionꢀ
temperatureꢀmayꢀimpairꢀdeviceꢀreliability.
Note 7:ꢀMeasurementꢀmadeꢀinꢀclosedꢀloopꢀlinearꢀregulatorꢀconfigurationꢀ
withꢀLV ꢀ=ꢀ1.2V,ꢀI
ꢀ=ꢀ10µA.
LOAD
OUT
Note 8:ꢀMeasurementꢀmadeꢀinꢀaꢀproprietaryꢀtestꢀmodeꢀwithꢀslopeꢀ
compensationꢀdisabled.
Note 9:ꢀMeasurementꢀisꢀassuredꢀbyꢀdesign,ꢀcharacterizationꢀandꢀstatisticalꢀ
processꢀcontrol.
W U
TYPICAL PERFOR A CE CHARACTERISTICS
Efficiency vs Input Voltage for
Buck (Burst)
Efficiency vs Input Voltage for
Buck (Pulse Skip)
Efficiency vs Load Current for
Buck (Burst)
100
95
90
85
80
75
70
65
60
55
50
100
95
90
85
80
75
70
65
60
55
50
100
90
80
70
60
50
40
30
20
10
0
V
= 1.8V
V
OUT
= 1.8V
OUT
V
= 2.7V
IN
I
= 500mA
I
I
= 500mA
= 30mA
OUT
V
= 4.2V
IN
OUT
OUT
V
= 3.6V
IN
I
= 100mA
OUT
I
= 100mA
OUT
I
= 30mA
OUT
V
= 1.8V
1
OUT
2
3
4
5
6
2
3
4
5
6
0.1
10
100
1000
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
LOAD CURRENT (mA)
35412 G03
35411 G01
35411 G02
Efficiency vs Load Current for
Buck (Burst)
Efficiency vs Load Current for
Buck (Pulse Skip)
Efficiency vs Load Current for
Buck (Pulse Skip)
100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
0
V
= 2.7V
V
= 2.5V
V
= 1.8V
IN
OUT
OUT
V
= 2.7V
IN
V
= 4.2V
V
= 2.7V
IN
IN
V
= 3.6V
IN
V
= 3.6V
IN
V
= 3.6V
V
= 4.2V
V
= 4.2V
IN
IN
IN
V
= 2.5V
1
OUT
0.1
10
100
1000
0.1
1
10
100
1000
0.1
1
10
100
1000
LOAD cURRENT (mA)
LOAD CURRENT (mA)
LOAD CURRENT (mA)
35411 G05
35411 G06
35411 G04
35411fa
ꢃ
LTC3541-1
W U
TYPICAL PERFOR A CE CHARACTERISTICS
Buck (Burst) Plus VLDO Bias
Current vs VLDO Load Current
Output (Auto Start-Up Sequence,
Buck in Pulse Skip) vs Time
VLDO Dropout Voltage vs
Load Current
100
80
250
200
150
100
50
V
= 1.5V
V
I
= 3.6V
OUT
IN
V
= 0
OUT
LOAD(BUCK)
V
= 3V
IN
2V/DIV
I
= I + I
– I
BIAS VIN LVIN LOAD
V
= 3.6V
IN
LV
2V/DIV
OUT
60
V
= 4.2V
IN
V
IN
40
2V/DIV
20
0
35411 G09
4ms/DIV
I
I
= 400mA
LVOUT
VOUT
= 30mA
0
0
100
150
200
250
300
0.1
1
10
100
50
1000
LOAD CURRENT (mA)
LOAD CURRENT (mA)
35411 G07
35411 G08
Oscillator Frequency
vs Temperature
Oscillator Frequency
vs Supply Voltage
VLDO/Linear Regulator Reference
vs Temperature
2.50
2.45
2.40
2.35
2.30
2.25
2.20
2.15
2.10
2.05
2.00
0.410
0.408
0.406
0.404
0.402
0.400
0.398
0.396
0.394
0.392
0.390
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
–50
0
25
75 100
–25
4
5
6
3
TEMPERATURE (°C)
SUPPLY VOLTAGE (V)
35411 G10
53411 G12
35411 G11
Buck (Burst) and VLDO Output
Buck Reference vs Temperature
RDS(ON) vs Temperature
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
IN
LV
OUT
10mV/DIV
AC COUPLED
V
OUT
10mV/DIV
SYNCH SWITCH
MAIN SWITCH
AC COUPLED
V
V
V
= 2.5V
= 3.6V
= 5.5V
35411 G15
IN
IN
IN
2µs/DIV
V
= 3.6V
OUT
IN
LV
= 1.5V
V
I
= 1.8V
= 50mA
OUT
–50
0
25
50
75 100 125
–50
25
50
75
100 125
–25
–25
0
LOAD
Burst Mode OPERATION
TEMPERATURE (°C)
TEMPERATURE (°C)
53411 G13
35411 G14
35411fa
ꢄ
LTC3541-1
W U
TYPICAL PERFOR A CE CHARACTERISTICS
Buck (Pulse Skip) Load Step from
1mA to 500mA
Buck (Burst) Load Step from
1mA to 500mA
VLDO Load Step from
1mA to 300mA
V
V
OUT
OUT
100mV/DIV
100mV/DIV
LV
OUT
AC COUPLED
AC COUPLED
20mV/DIV
AC COUPLED
I
I
L
L
500mA/DIV
500mA/DIV
I
I
I
LOAD
LOAD
LOAD
250mA/DIV
500mA/DIV
500mA/DIV
35411 G16
35411 G18
35411 G17
40µs/DIV
V
V
I
= 3.6V
400µs/DIV
= 1mA TO 300mA
V
= 3.6V
OUT
40µs/DIV
V
V
I
= 3.6V
IN
OUT
IN
IN
OUT
= 1.8V
= 1mA TO 500mA
LV
I
= 1.5V
= 1.8V
= 1mA TO 500mA
LOAD
LOAD
LOAD
VLDO Load Step from
100mA to 300mA
Linear Regulator to VLDO
Transition, Load = 1mA
Linear Regulator to VLDO
Transition, Load = 30mA
L
VOUT
10mV/DIV
LV
LV
OUT
OUT
AC COUPLED
20mV/DIV
10mV/DIV
AC COUPLED
AC COUPLED
V
OUT
10mV/DIV
AC COUPLED
I
LOAD
I
LOAD
50mA/DIV
250mA/DIV
35411 G19
35411 G20
35412 G2
400µs/DIV
= 100mA TO 300mA
40µs/DIV
V
= 3.6V
OUT
V
= 3.6V
IN
V
LV
V
= 3.6V
2µs/DIV
IN
IN
LV
I
= 1.5V
LV
I
= 1.5V
= 1.5V
OUT
OUT
= 1.875V
= 1mA
LOAD
LOAD
OUT
VLDO to Linear Regulator
Transition, Load = 1mA
VLDO to Linear Regulator
Transition, Load = 30mA
LV
LV
OUT
OUT
10mV/DIV
10mV/DIV
AC COUPLED
AC COUPLED
I
LOAD
I
LOAD
50mA/DIV
50mA/DIV
35411 G22
35411 G23
40µs/DIV
V
= 3.6V
40µs/DIV
V
= 3.6V
IN
IN
LV
I
= 1.5V
LV
I
= 1.5V
OUT
OUT
= 1mA
= 30mA
LOAD
LOAD
35411fa
ꢅ
LTC3541-1
U U
U
PI FU CTIO S
V
(Pin 1):ꢀMainꢀSupplyꢀPin.ꢀThisꢀpinꢀmustꢀbeꢀcloselyꢀ
MODE (Pin 8):ꢀBuckꢀModeꢀSelectionꢀPin.ꢀThisꢀpinꢀenablesꢀ
buckꢀPulse-Skipꢀoperationꢀwhenꢀdrivenꢀtoꢀaꢀlogicꢀhighꢀ
andꢀenablesꢀbuckꢀBurstꢀModeꢀoperationꢀwhenꢀdrivenꢀtoꢀ
aꢀlogicꢀlow.
IN
decoupledꢀtoꢀGNDꢀwithꢀaꢀ10µFꢀorꢀgreaterꢀcapacitor.
ENBUCK (Pin 2):ꢀBuckꢀEnableꢀPin.ꢀThisꢀpinꢀenablesꢀtheꢀ
buckꢀregulatorꢀwhenꢀdrivenꢀtoꢀaꢀlogicꢀhigh.
ENVLDO (Pin 9):ꢀ VLDO/Linearꢀ Regulatorꢀ Enableꢀ Pin.ꢀ
Whenꢀdrivenꢀtoꢀaꢀlogicꢀhigh,ꢀthisꢀpinꢀenablesꢀtheꢀlinearꢀ
regulatorꢀwhenꢀtheꢀENBUCKꢀpinꢀisꢀdrivenꢀtoꢀaꢀlogicꢀlow,ꢀ
andꢀenablesꢀtheꢀVLDOꢀwhenꢀtheꢀENBUCKꢀpinꢀisꢀdrivenꢀtoꢀ
aꢀlogicꢀhigh.
BUCKFB (Pin 3):ꢀBuckꢀRegulatorꢀFeedbackꢀPin.ꢀThisꢀpinꢀ
receivesꢀtheꢀbuckꢀregulator’sꢀfeedbackꢀvoltageꢀfromꢀanꢀ
externalꢀresistiveꢀdivider.
LFB (Pin 4):ꢀVLDO/LinearꢀRegulatorꢀFeedbackꢀPin.ꢀThisꢀ
pinꢀreceivesꢀeitherꢀtheꢀVLDOꢀorꢀlinearꢀregulator’sꢀfeedbackꢀ
voltageꢀfromꢀanꢀexternalꢀresistiveꢀdivider.
SW (Pin 10):ꢀSwitchꢀNodeꢀPin.ꢀThisꢀpinꢀconnectsꢀtheꢀ
internalꢀmainꢀandꢀsynchronousꢀpowerꢀMOSFETꢀswitchesꢀ
toꢀtheꢀexternalꢀinductorꢀforꢀtheꢀbuckꢀregulator.
LV
(Pin 5):ꢀVLDO/LinearꢀRegulatorꢀOutputꢀPin.ꢀThisꢀ
OUT
pinꢀprovidesꢀtheꢀregulatedꢀoutputꢀvoltageꢀfromꢀtheꢀVLDOꢀ
Exposed Pad (Pin 11):ꢀGroundꢀPin.ꢀThisꢀpinꢀmustꢀbeꢀ
solderedꢀtoꢀtheꢀPCBꢀtoꢀprovideꢀbothꢀelectricalꢀcontactꢀtoꢀ
groundꢀandꢀgoodꢀthermalꢀcontactꢀtoꢀtheꢀPCB.
orꢀlinearꢀregulator.
LV (Pin 6):ꢀVLDO/LinearꢀRegulatorꢀInputꢀSupplyꢀPin.ꢀ
IN
ThisꢀpinꢀprovidesꢀtheꢀinputꢀsupplyꢀvoltageꢀforꢀtheꢀVLDOꢀ
Note:ꢀTableꢀ1ꢀdetailsꢀtheꢀtruthꢀtableꢀforꢀtheꢀcontrolꢀpinsꢀ
ofꢀtheꢀLTC3541-1.
powerꢀFET.
GND (Pin 7):ꢀAnalogꢀGroundꢀPin.
Table 1. LTC3541-1 Control Pin Truth Table
PIN NAME
OPERATIONAL DESCRIPTION
ENBUCK ENVLDO MODE
0
0
0
1
X
X
LTC3541-1ꢀPoweredꢀDown
BuckꢀPoweredꢀDown,ꢀVLDOꢀRegulatorꢀ
PoweredꢀDown,ꢀLinearꢀRegulatorꢀ
Enabled
1
1
1
1
0
0
1
1
0
1
0
1
BuckꢀEnabled,ꢀVLDOꢀRegulatorꢀPoweredꢀ
Down,ꢀLinearꢀRegulatorꢀPoweredꢀDown, ꢀ
BurstꢀModeꢀOperation
BuckꢀEnabled,ꢀVLDOꢀRegulatorꢀPoweredꢀ
Down,ꢀLinearꢀRegulatorꢀPoweredꢀDown,ꢀꢀ
Pulse-SkipꢀModeꢀOperation
BuckꢀEnabled,ꢀVLDOꢀRegulatorꢀEnabled,ꢀ
LinearꢀRegulatorꢀPoweredꢀDown,ꢀBurstꢀ
ModeꢀOperation
BuckꢀEnabled,ꢀVLDOꢀRegulatorꢀEnabled,ꢀ
LinearꢀRegulatorꢀPoweredꢀDown,ꢀPulse-
SkipꢀModeꢀOperation
35411fa
ꢆ
LTC3541-1
U
U
W
FU CTIO AL BLOCK DIAGRA
2.2µH
I
= 500mA
OUT(BUCK)
V
≥ LV
+ 1.4V
OUT
IN(MIN)
10µF
10
SW
V
IN
1
500mA BUCK
SW
V
IN
22pF
REF
FB
GND
BUCKFB
3
6
PGND
LV
IN
VLDO/LINEAR REG
V
LV
IN
IN
REF
REF
LV
< V – 1.4V
IN
ENBUCK
ENVLDO
MODE
OUT(MAX)
+
2
9
8
I
I
= 300mA (VLDO REG)
= 30mA (LINEAR REG)
OUT
OUT
CONTROL
LOGIC
LFB
LV
–
OUT
5
4
CNTRL
GND
2.2µF
LFB
GND
PGND
11
7
35411 F01
Figure 1. LTC3541-1 Functional Block Diagram
U
OPERATIO
TheꢀLTC3541-1ꢀcontainsꢀaꢀhighꢀefficiencyꢀsynchronousꢀ
buckꢀconverter,ꢀaꢀveryꢀlowꢀdropoutꢀregulatorꢀ(VLDO)ꢀandꢀ
aꢀlinearꢀregulator.ꢀItꢀcanꢀbeꢀusedꢀtoꢀprovideꢀupꢀtoꢀtwoꢀ
outputꢀvoltagesꢀfromꢀaꢀsingleꢀinputꢀvoltageꢀmakingꢀtheꢀ
LTC3541-1ꢀidealꢀforꢀapplicationsꢀwithꢀlimitedꢀboardꢀspace.ꢀ
Theꢀcombinationꢀandꢀconfigurationꢀofꢀtheseꢀmajorꢀblocksꢀ
withinꢀtheꢀLTC3541-1ꢀisꢀdeterminedꢀbyꢀwayꢀofꢀtheꢀcontrolꢀ
pinsꢀENBUCKꢀandꢀENVLDOꢀasꢀdefinedꢀinꢀTableꢀ1.
intoꢀconsiderationꢀwhenꢀusingꢀtheꢀbuckꢀregulatorꢀtoꢀprovideꢀ
theꢀpowerꢀforꢀbothꢀtheꢀVLDOꢀandꢀforꢀexternalꢀloads.ꢀ
WithꢀtheꢀENBUCKꢀpinꢀdrivenꢀtoꢀaꢀlogicꢀlowꢀandꢀENVLDOꢀ
drivenꢀtoꢀaꢀlogicꢀhigh,ꢀtheꢀLTC3541-1ꢀenablesꢀtheꢀlinearꢀ
regulator,ꢀprovidingꢀaꢀlowꢀnoiseꢀregulatedꢀoutputꢀvoltageꢀ
atꢀtheꢀLV ꢀpinꢀwhileꢀdrawingꢀminimalꢀquiescentꢀcurrentꢀ
OUT
fromꢀtheꢀV ꢀinputꢀpin.ꢀThisꢀfeatureꢀallowsꢀoutputꢀvoltageꢀ
IN
LV ꢀtoꢀbeꢀbroughtꢀintoꢀregulationꢀwithoutꢀtheꢀpresenceꢀ
OUT
WithꢀtheꢀENBUCKꢀpinꢀdrivenꢀtoꢀaꢀlogicꢀhighꢀandꢀENVLDOꢀ
drivenꢀtoꢀaꢀlogicꢀlow,ꢀtheꢀLTC3541-1ꢀenablesꢀtheꢀbuckꢀ
converterꢀ toꢀ efficientlyꢀ reduceꢀ theꢀ voltageꢀ providedꢀ atꢀ
ofꢀtheꢀLV ꢀvoltage.ꢀ
IN
Withꢀ theꢀ ENBUCKꢀ andꢀ ENVLDOꢀ pinsꢀ bothꢀ drivenꢀ toꢀ aꢀ
logicꢀ high,ꢀ theꢀ LTC3541-1ꢀ enablesꢀ theꢀ highꢀ efficiencyꢀ
buckꢀconverterꢀandꢀVLDOꢀregulator,ꢀprovidingꢀdualꢀoutputꢀ
operationꢀfromꢀaꢀsingleꢀinputꢀvoltage.ꢀWhenꢀconfiguredꢀ
inꢀthisꢀmanner,ꢀtheꢀLTC3541-1’sꢀautoꢀstart-upꢀsequencingꢀ
featureꢀwillꢀbringꢀtheꢀVLDO/linearꢀregulatorꢀoutputꢀintoꢀ
regulationꢀinꢀaꢀcontrolledꢀmannerꢀpriorꢀtoꢀenablingꢀtheꢀ
theꢀV ꢀinputꢀpinꢀtoꢀanꢀoutputꢀvoltageꢀwhichꢀisꢀsetꢀbyꢀanꢀ
IN
externalꢀfeedbackꢀresistorꢀnetwork.ꢀTheꢀbuckꢀregulatorꢀ
canꢀbeꢀconfiguredꢀforꢀPulse-SkipꢀorꢀBurstꢀModeꢀopera-
tionꢀbyꢀdrivingꢀtheꢀMODEꢀpinꢀtoꢀaꢀlogicꢀhighꢀorꢀlogicꢀlowꢀ
respectively.ꢀTheꢀbuckꢀregulatorꢀisꢀcapableꢀofꢀprovidingꢀaꢀ
maximumꢀoutputꢀcurrentꢀofꢀ500mA,ꢀwhichꢀmustꢀbeꢀtakenꢀ
35411fa
ꢇ
LTC3541-1
U
OPERATIO
buckꢀregulatorꢀwithoutꢀtheꢀneedꢀforꢀexternalꢀpinꢀcontrol.ꢀ
AꢀdetailedꢀdiscussionꢀofꢀtheꢀtransitionsꢀbetweenꢀtheꢀVLDOꢀ
andꢀ linearꢀ regulatorꢀ canꢀ beꢀ foundꢀ inꢀ theꢀ VLDO/Linearꢀ
RegulatorꢀLoopꢀsection.ꢀ
WhenꢀtheꢀMODEꢀpinꢀisꢀdrivenꢀtoꢀaꢀlogicꢀhighꢀtheꢀLTC3541-1ꢀ
operatesꢀinꢀPulse-Skipꢀmodeꢀforꢀlowꢀoutputꢀvoltageꢀripple.ꢀ
Inꢀthisꢀmode,ꢀtheꢀLTC3541-1ꢀcontinuesꢀtoꢀswitchꢀatꢀaꢀ
constantꢀfrequencyꢀdownꢀtoꢀveryꢀlowꢀcurrents,ꢀwhereꢀitꢀ
willꢀbeginꢀskippingꢀpulsesꢀusedꢀtoꢀcontrolꢀtheꢀmainꢀ(top)ꢀ
switchꢀtoꢀmaintainꢀtheꢀproperꢀaverageꢀinductorꢀcurrent.
Buck Regulator Control Loop
TheꢀLTC3541-1ꢀinternalꢀbuckꢀregulatorꢀusesꢀaꢀconstantꢀ
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.
Ifꢀtheꢀinputꢀsupplyꢀvoltageꢀisꢀdecreasedꢀtoꢀaꢀvalueꢀap-
proachingꢀtheꢀoutputꢀvoltage,ꢀtheꢀdutyꢀcycleꢀofꢀtheꢀbuckꢀ
isꢀincreasedꢀtowardꢀmaximumꢀon-timeꢀandꢀ100%ꢀdutyꢀ
cycle.ꢀTheꢀoutputꢀvoltageꢀwillꢀthenꢀbeꢀdeterminedꢀbyꢀtheꢀ
inputꢀvoltageꢀminusꢀtheꢀvoltageꢀdropꢀacrossꢀtheꢀmainꢀ
switchꢀandꢀtheꢀinductor.
VLDO/Linear Regulator Loop
InꢀtheꢀLTC3541-1,ꢀtheꢀVLDOꢀandꢀlinearꢀregulatorꢀloopsꢀ
consistꢀofꢀanꢀamplifierꢀandꢀN-channelꢀMOSFETꢀoutputꢀ
stagesꢀ that,ꢀ whenꢀ connectedꢀ withꢀ theꢀ properꢀ externalꢀ
components,ꢀwillꢀservoꢀtheꢀoutputꢀtoꢀmaintainꢀaꢀregula-
Theꢀpeakꢀinductorꢀcurrentꢀisꢀdeterminedꢀbyꢀcomparingꢀtheꢀ
buckꢀfeedbackꢀsignalꢀtoꢀanꢀinternalꢀ0.8Vꢀreference.ꢀWhenꢀ
theꢀloadꢀcurrentꢀincreases,ꢀtheꢀoutputꢀofꢀtheꢀbuckꢀandꢀ
henceꢀtheꢀbuckꢀfeedbackꢀsignalꢀdecrease.ꢀThisꢀdecreaseꢀ
causesꢀtheꢀpeakꢀinductorꢀcurrentꢀtoꢀincreaseꢀuntilꢀtheꢀaver-
ageꢀinductorꢀcurrentꢀmatchesꢀtheꢀloadꢀcurrent.ꢀWhileꢀtheꢀ
mainꢀswitchꢀisꢀoff,ꢀtheꢀsynchronousꢀswitchꢀisꢀturnedꢀonꢀ
untilꢀeitherꢀtheꢀinductorꢀcurrentꢀstartsꢀtoꢀreverseꢀdirectionꢀ
orꢀtheꢀbeginningꢀofꢀaꢀnewꢀclockꢀcycle.
torꢀoutputꢀvoltage,ꢀLV .ꢀTheꢀinternalꢀreferenceꢀvoltageꢀ
OUT
providedꢀtoꢀtheꢀamplifierꢀisꢀ0.4Vꢀallowingꢀforꢀaꢀwideꢀrangeꢀ
ofꢀoutputꢀvoltages.ꢀLoopꢀconfigurationsꢀenablingꢀtheꢀVLDOꢀ
orꢀtheꢀlinearꢀregulatorꢀareꢀstableꢀwithꢀanꢀoutputꢀcapacitanceꢀ
asꢀlowꢀasꢀ2.2µFꢀandꢀasꢀhighꢀasꢀ100µF.ꢀBothꢀtheꢀVLDOꢀ
andꢀtheꢀlinearꢀregulatorsꢀareꢀcapableꢀofꢀoperatingꢀwithꢀanꢀ
inputꢀvoltage,ꢀV ,ꢀasꢀlowꢀasꢀ2.7V,ꢀbutꢀareꢀsubjectꢀtoꢀtheꢀ
IN
constraintꢀthatꢀV ꢀmustꢀbeꢀgreaterꢀthanꢀLV ꢀ+ꢀ1.4V.ꢀ
IN
OUT
TheꢀVLDOꢀisꢀdesignedꢀtoꢀprovideꢀupꢀtoꢀ300mAꢀofꢀoutputꢀ
currentꢀatꢀaꢀveryꢀlowꢀLV ꢀtoꢀLV ꢀvoltage.ꢀThisꢀallowsꢀ
WhenꢀtheꢀMODEꢀpinꢀisꢀdrivenꢀtoꢀaꢀlogicꢀlow,ꢀtheꢀLTC3541-1ꢀ
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.
IN
OUT
aꢀclean,ꢀsecondary,ꢀanalogꢀsupplyꢀvoltageꢀtoꢀbeꢀprovidedꢀ
withꢀaꢀminimumꢀdropꢀinꢀefficiency.ꢀTheꢀVLDOꢀisꢀprovidedꢀ
withꢀthermalꢀprotectionꢀthatꢀisꢀdesignedꢀtoꢀdisableꢀtheꢀ
VLDOꢀfunctionꢀwhenꢀtheꢀoutput,ꢀpassꢀtransistor’sꢀjunctionꢀ
temperatureꢀreachesꢀapproximatelyꢀ160°C.ꢀInꢀadditionꢀtoꢀ
thermalꢀprotection,ꢀshort-circuitꢀdetectionꢀisꢀprovidedꢀtoꢀ
disableꢀtheꢀVLDOꢀfunctionꢀwhenꢀaꢀshort-circuitꢀconditionꢀ
isꢀsensed.ꢀThisꢀcircuitꢀisꢀdesignedꢀsuchꢀthatꢀanꢀoutputꢀ
currentꢀofꢀapproximatelyꢀ1Aꢀcanꢀbeꢀprovidedꢀbeforeꢀthisꢀ
circuitꢀwillꢀtrigger.ꢀAsꢀdetailedꢀinꢀtheꢀElectricalꢀCharacter-
istics,ꢀtheꢀVLDOꢀregulatorꢀwillꢀbeꢀoutꢀofꢀregulationꢀwhenꢀ
thisꢀeventꢀoccurs.ꢀBothꢀtheꢀthermalꢀandꢀshort-circuitꢀfaultsꢀ
whenꢀdetectedꢀareꢀtreatedꢀasꢀcatastrophicꢀfaultꢀcondi-
35411fa
ꢈ
LTC3541-1
U
OPERATIO
tions.ꢀTheꢀLTC3541-1ꢀwillꢀbeꢀresetꢀuponꢀtheꢀdetectionꢀofꢀ
eitherꢀevent.ꢀTheꢀN-channelꢀMOSFETꢀincorporatedꢀinꢀtheꢀ
TransitioningꢀfromꢀlinearꢀregulatorꢀmodeꢀtoꢀVLDOꢀmode,ꢀ
accomplishedꢀbyꢀbringingꢀENBUCKꢀfromꢀaꢀlogicꢀlowꢀtoꢀaꢀ
logicꢀhighꢀwhileꢀENVLDOꢀisꢀaꢀlogicꢀhigh,ꢀisꢀdesignedꢀtoꢀbeꢀ
asꢀseamlessꢀandꢀtransientꢀfreeꢀasꢀpossible.ꢀTheꢀpreciseꢀ
VLDOꢀhasꢀitsꢀdrainꢀconnectedꢀtoꢀtheꢀLV ꢀpinꢀasꢀshownꢀ
IN
inꢀFigureꢀ1.ꢀToꢀensureꢀreliableꢀoperation,ꢀtheꢀLV ꢀvoltageꢀ
IN
mustꢀbeꢀstableꢀbeforeꢀtheꢀVLDOꢀisꢀenabled.ꢀForꢀtheꢀcaseꢀ
transientꢀresponseꢀofꢀLV ꢀdueꢀtoꢀthisꢀtransitionꢀisꢀaꢀ
OUT
whereꢀtheꢀvoltageꢀonꢀtheꢀLV ꢀpinꢀisꢀsuppliedꢀbyꢀtheꢀbuckꢀ
functionꢀofꢀC ꢀandꢀtheꢀloadꢀcurrent.ꢀWaveformsꢀgivenꢀ
IN
OUT
regulator,ꢀtheꢀinternalꢀpowerꢀsupplyꢀsequencingꢀlogicꢀas-
suresꢀvoltagesꢀareꢀappliedꢀinꢀtheꢀappropriateꢀmanner.ꢀForꢀ
theꢀcaseꢀwhereꢀanꢀexternalꢀsupplyꢀisꢀusedꢀtoꢀpowerꢀtheꢀ
LV ꢀpin,ꢀtheꢀvoltageꢀonꢀtheꢀLV ꢀpinꢀmustꢀbeꢀstableꢀbeforeꢀ
inꢀtheꢀTypicalꢀPerformanceꢀCharaceristicsꢀshowꢀtypicalꢀ
transientꢀresponsesꢀusingꢀtheꢀminimumꢀC ꢀofꢀ2.2µFꢀandꢀ
OUT
loadꢀcurrentsꢀofꢀ1mAꢀandꢀ30mAꢀrespectively.ꢀGenerally,ꢀtheꢀ
amplitudeꢀofꢀanyꢀtransientsꢀpresentꢀwillꢀdecreaseꢀasꢀC
ꢀ
IN
IN
OUT
theꢀENVLDOꢀpinꢀisꢀbroughtꢀfromꢀaꢀlowꢀtoꢀaꢀhigh.ꢀFurther,ꢀ
isꢀincreased.ꢀToꢀensureꢀreliableꢀoperationꢀandꢀadherenceꢀ
toꢀtheꢀloadꢀregulationꢀlimitsꢀpresentedꢀinꢀtheꢀElectricalꢀ
Characteristicsꢀtable,ꢀtheꢀloadꢀcurrentꢀmustꢀnotꢀexceedꢀ
theꢀexternalꢀLV ꢀvoltageꢀmustꢀbeꢀreducedꢀinꢀconjunctionꢀ
IN
withꢀV ꢀwheneverꢀV ꢀisꢀpulledꢀlowꢀorꢀremoved.
IN
IN
theꢀlinearꢀregulatorꢀI ꢀlimitꢀofꢀ30mAꢀwithinꢀ20msꢀafterꢀ
OUT
Theꢀlinearꢀregulatorꢀisꢀdesignedꢀtoꢀprovideꢀaꢀlowerꢀoutputꢀ
currentꢀ(30mA)ꢀthanꢀthatꢀavailableꢀfromꢀtheꢀVLDO.ꢀTheꢀ
linearꢀregulator’sꢀoutputꢀpassꢀtransistorꢀhasꢀitsꢀdrainꢀtiedꢀ
ENBUCKꢀhasꢀtransitionedꢀtoꢀaꢀlogicꢀhigh.ꢀTheꢀ300mAꢀI
ꢀ
OUT
limitꢀofꢀVLDOꢀappliesꢀthereafter.ꢀFurther,ꢀforꢀconfigurationsꢀ
thatꢀdoꢀnotꢀuseꢀtheꢀLTC3541-1’sꢀbuckꢀregulatorꢀtoꢀprovideꢀ
toꢀtheꢀV ꢀrail.ꢀThisꢀallowsꢀtheꢀlinearꢀregulatorꢀtoꢀbeꢀturnedꢀ
IN
theꢀVLDOꢀinputꢀvoltageꢀ(LV ),ꢀtheꢀuserꢀmustꢀensureꢀaꢀ
IN
onꢀpriorꢀto,ꢀandꢀindependentꢀof,ꢀtheꢀbuckꢀregulatorꢀwhichꢀ
wouldꢀordinarilyꢀdriveꢀtheꢀVLDOꢀinꢀaꢀtypicalꢀapplication.ꢀ
Theꢀlinearꢀregulatorꢀisꢀprovidedꢀwithꢀthermalꢀprotectionꢀthatꢀ
isꢀdesignedꢀtoꢀdisableꢀtheꢀlinearꢀregulatorꢀfunctionꢀwhenꢀ
theꢀoutputꢀpassꢀtransistor’sꢀjunctionꢀtemperatureꢀreachesꢀ
approximatelyꢀ160°C.ꢀInꢀadditionꢀtoꢀthermalꢀprotection,ꢀ
short-circuitꢀdetectionꢀisꢀprovidedꢀtoꢀdisableꢀtheꢀlinearꢀ
regulatorꢀfunctionꢀwhenꢀaꢀshort-circuitꢀconditionꢀisꢀsensed.ꢀ
Thisꢀcircuitꢀisꢀdesignedꢀsuchꢀthatꢀanꢀoutputꢀcurrentꢀofꢀ
approximatelyꢀ120mAꢀcanꢀbeꢀprovidedꢀbeforeꢀthisꢀcircuitꢀ
willꢀtrigger.ꢀAsꢀdetailedꢀinꢀtheꢀElectricalꢀCharacteristics,ꢀ
theꢀlinearꢀregulatorꢀwillꢀbeꢀoutꢀofꢀregulationꢀwhenꢀthisꢀ
eventꢀoccurs.ꢀBothꢀtheꢀthermalꢀandꢀshort-circuitꢀfaultsꢀareꢀ
treatedꢀasꢀcatastrophicꢀfaultꢀconditions.ꢀTheꢀLTC3541-1ꢀ
willꢀbeꢀresetꢀuponꢀtheꢀdetectionꢀofꢀeitherꢀevent.ꢀ
stableꢀLV ꢀvoltageꢀisꢀpresentꢀnoꢀlessꢀthanꢀ1msꢀpriorꢀtoꢀ
IN
ENBUCKꢀtransitioningꢀtoꢀaꢀlogicꢀhigh.
Inꢀaꢀsimilarꢀmanner,ꢀtransitioningꢀfromꢀVLDOꢀmodeꢀtoꢀ
linearꢀregulatorꢀmode,ꢀaccomplishedꢀbyꢀbringingꢀENBUCKꢀ
fromꢀaꢀlogicꢀhighꢀꢀtoꢀaꢀlogicꢀlowꢀwhileꢀENVLDOꢀisꢀaꢀlogicꢀ
high,ꢀisꢀdesignedꢀtoꢀbeꢀasꢀseamlessꢀandꢀtransientꢀfreeꢀasꢀ
possible.ꢀAgain,ꢀtheꢀpreciseꢀtransientꢀresponseꢀofꢀLV
ꢀ
OUT
dueꢀtoꢀthisꢀtransitionꢀisꢀaꢀfunctionꢀofꢀC ꢀandꢀtheꢀloadꢀ
OUT
current.ꢀ Waveformsꢀ givenꢀ inꢀ theꢀ Typicalꢀ Performanceꢀ
Characeristicsꢀ showꢀ typicalꢀ transientꢀ responsesꢀ usingꢀ
theꢀminimumꢀC ꢀofꢀ2.2µFꢀandꢀloadꢀcurrentsꢀofꢀ1mAꢀ
OUT
andꢀ30mAꢀrespectively.ꢀGenerally,ꢀtheꢀamplitudeꢀofꢀanyꢀ
transientsꢀpresentꢀwillꢀdecreaseꢀasꢀC ꢀisꢀincreased.ꢀToꢀ
OUT
ensureꢀreliableꢀoperationꢀandꢀadherenceꢀtoꢀtheꢀloadꢀregula-
tionꢀlimitsꢀpresentedꢀinꢀtheꢀElectricalꢀCharactersticsꢀtable,ꢀ
TheꢀN-channelꢀMOSFETꢀincorporatedꢀinꢀtheꢀlinearꢀregulatorꢀ
theꢀloadꢀcurrentꢀmustꢀnotꢀexceedꢀtheꢀlinearꢀregulatorꢀI
ꢀ
OUT
hasꢀitsꢀdrainꢀconnectedꢀtoꢀtheꢀV ꢀpinꢀasꢀshownꢀinꢀFigureꢀ1.ꢀ
IN
limitꢀofꢀ30mAꢀ1msꢀpriorꢀtoꢀENBUCKꢀtransitioningꢀtoꢀaꢀlogicꢀ
lowꢀandꢀthereafer.ꢀFurther,ꢀforꢀconfigurationsꢀthatꢀdoꢀnotꢀ
useꢀtheꢀLTC3541-1’sꢀbuckꢀregulatorꢀtoꢀprovideꢀtheꢀVLDOꢀ
TheꢀsizeꢀofꢀthisꢀMOSFETꢀandꢀitsꢀassociatedꢀpowerꢀbussingꢀ
isꢀdesignedꢀtoꢀaccommodateꢀ30mAꢀofꢀDCꢀcurrent.ꢀCurrentsꢀ
aboveꢀthisꢀcanꢀbeꢀsupportedꢀforꢀshortꢀperiodsꢀasꢀstipulatedꢀ
inꢀtheꢀAbsoluteꢀMaximumꢀRatingsꢀsection.
inputꢀvoltageꢀ(LV ),ꢀtheꢀuserꢀmustꢀcontinueꢀtoꢀensureꢀaꢀ
IN
stableꢀLV ꢀvoltageꢀnoꢀlessꢀthanꢀ1msꢀafterꢀENBUCKꢀhasꢀ
IN
transitionedꢀtoꢀaꢀlogicꢀlow.
35411fa
ꢀ0
LTC3541-1
U U
W U
APPLICATIO S I FOR ATIO
TheꢀbasicꢀLTC3541-1ꢀapplicationꢀcircuitꢀisꢀshownꢀonꢀtheꢀ
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
2.0ꢀ
1.5ꢀ
1.3ꢀ
1.1
3.9ꢀ×ꢀ3.9ꢀ×ꢀ2.4
ofꢀL,ꢀfollowedꢀbyꢀC ,ꢀC ,ꢀandꢀfeedbackꢀresistorꢀvaluesꢀ
IN OUT
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
1.0ꢀ
1.3
Forꢀmostꢀapplications,ꢀtheꢀappropriateꢀinductorꢀvalueꢀwillꢀ
beꢀinꢀtheꢀrangeꢀofꢀ1.5µHꢀtoꢀ3.3µHꢀwithꢀ2.2µHꢀtheꢀmostꢀ
commonlyꢀ used.ꢀ Theꢀ exactꢀ inductorꢀ valueꢀ isꢀ chosenꢀ
largelyꢀ basedꢀ onꢀ theꢀ desiredꢀ rippleꢀ currentꢀ andꢀ burstꢀ
rippleꢀperformance.ꢀGenerally,ꢀlargeꢀvalueꢀinductorsꢀre-
duceꢀrippleꢀcurrent,ꢀandꢀconversely,ꢀsmallꢀvalueꢀinductorsꢀ
Murataꢀ
LQH3C
1.0ꢀ
2.2
0.060ꢀ
0.097
1.00ꢀ
0.79
2.5ꢀ×ꢀ3.2ꢀ×ꢀ2.0
3.2ꢀ×ꢀ3.2ꢀ×ꢀ1.2ꢀ
Sumidaꢀ
CDRH2D11/HP
1.5ꢀ
2.2
0.06ꢀ
0.10
1.00ꢀ
0.72
C and C
IN
Selection
OUT
produceꢀhigherꢀrippleꢀcurrent.ꢀHigherꢀV ꢀorꢀV ꢀmayꢀ
IN
OUT
Inꢀcontinuousꢀmode,ꢀtheꢀsourceꢀcurrentꢀofꢀtheꢀtopꢀMOSFETꢀ
isꢀaꢀsquareꢀwaveꢀofꢀdutyꢀcycleꢀV /V .ꢀToꢀpreventꢀlargeꢀ
voltageꢀtransients,ꢀaꢀlowꢀESRꢀinputꢀcapacitorꢀsizedꢀforꢀtheꢀ
maximumꢀRMSꢀcurrentꢀmustꢀbeꢀused.ꢀTheꢀmaximumꢀRMSꢀ
capacitorꢀcurrentꢀisꢀgivenꢀby:
alsoꢀincreaseꢀtheꢀrippleꢀcurrentꢀasꢀshownꢀinꢀEquationꢀ1.ꢀ
OUT IN
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.ꢀThisꢀsimpleꢀworst-caseꢀconditionꢀisꢀcommon-
RMS OUT
lyꢀusedꢀforꢀdesign.ꢀNoteꢀthatꢀtheꢀcapacitorꢀmanufacturer’sꢀ
rippleꢀcurrentꢀratingsꢀareꢀoftenꢀbasedꢀonꢀ2000ꢀhoursꢀofꢀ
life.ꢀThisꢀmakesꢀitꢀadvisableꢀtoꢀfurtherꢀderateꢀtheꢀcapaci-
torꢀorꢀchooseꢀaꢀcapacitorꢀratedꢀatꢀaꢀhigherꢀtemperatureꢀ
thanꢀrequired.ꢀAlwaysꢀconsultꢀtheꢀmanufacturerꢀwithꢀanyꢀ
questionꢀregardingꢀproperꢀcapacitorꢀchoice.
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
TheꢀselectionꢀofꢀC ꢀforꢀtheꢀbuckꢀregulatorꢀisꢀdrivenꢀbyꢀ
OUT
theꢀdesiredꢀbuckꢀloopꢀtransientꢀresponse,ꢀrequiredꢀeffectiveꢀ
seriesꢀresistanceꢀ(ESR)ꢀandꢀburstꢀrippleꢀperformance.
TheꢀLTC3541-1ꢀminimizesꢀtheꢀrequiredꢀnumberꢀofꢀexternalꢀ
componentsꢀ byꢀ providingꢀ internalꢀ loopꢀ compensationꢀ
forꢀtheꢀbuckꢀregulatorꢀloop.ꢀLoopꢀstability,ꢀtransientꢀre
-
ratherꢀthanꢀwhatꢀtheꢀLTC3541-1ꢀrequiresꢀtoꢀoperate.ꢀTableꢀ2ꢀ sponseꢀandꢀburstꢀperformanceꢀcanꢀbeꢀtailoredꢀbyꢀchoiceꢀ
showsꢀsomeꢀtypicalꢀsurfaceꢀmountꢀinductorsꢀthatꢀworkꢀ ofꢀoutputꢀcapacitance.ꢀForꢀmanyꢀapplications,ꢀdesirableꢀ
wellꢀinꢀLTC3541-1ꢀapplications.
stability,ꢀtransientꢀresponseꢀandꢀrippleꢀperformanceꢀcanꢀ
35411fa
ꢀꢀ
LTC3541-1
U U
W U
APPLICATIO S I FOR ATIO
beꢀobtainedꢀbyꢀchoosingꢀanꢀoutputꢀcapacitorꢀvalueꢀofꢀ
10µFꢀtoꢀ22µF.ꢀTypically,ꢀonceꢀtheꢀESRꢀrequirementꢀforꢀ
COUTꢀhasꢀbeenꢀmet,ꢀtheꢀRMSꢀcurrentꢀratingꢀgenerallyꢀfarꢀ
exceedsꢀtheꢀIRIPPLE(P-P)ꢀrequirement.ꢀTheꢀoutputꢀrippleꢀ
ΔVOUTꢀisꢀdeterminedꢀby:
Whenꢀchoosingꢀtheꢀinputꢀandꢀoutputꢀceramicꢀcapacitors,ꢀ
chooseꢀtheꢀX5RꢀorꢀX7Rꢀdielectricꢀformulations.ꢀTheseꢀ
dielectricsꢀhaveꢀtheꢀbestꢀtemperatureꢀandꢀvoltageꢀcharac-
teristicsꢀofꢀallꢀtheꢀceramicsꢀforꢀaꢀgivenꢀvalueꢀandꢀsize.
Output Voltage Programming
1
ΔVOUT ≅ ΔIL ESR+
TheꢀoutputꢀvoltageꢀisꢀsetꢀbyꢀtyingꢀBUCKFBꢀtoꢀaꢀresistiveꢀ
dividerꢀaccordingꢀtoꢀtheꢀfollowingꢀformula:
8fc
OUT
ꢀ
whereꢀfꢀ=ꢀoperatingꢀfrequency,ꢀC ꢀ=ꢀoutputꢀcapacitanceꢀ
OUT
R2
R1
andꢀΔI ꢀ=ꢀrippleꢀcurrentꢀinꢀtheꢀinductor.ꢀForꢀaꢀfixedꢀoutputꢀ
L
VOUT = 0.8V 1+
voltage,ꢀtheꢀoutputꢀrippleꢀisꢀhighestꢀatꢀmaximumꢀinputꢀ
ꢀ
voltageꢀsinceꢀΔI ꢀincreasesꢀwithꢀinputꢀvoltage.
L
SinceꢀtheꢀimpedanceꢀatꢀtheꢀBUCKFBꢀpinꢀisꢀdependantꢀuponꢀ
theꢀresistorꢀdividerꢀnetworkꢀused,ꢀandꢀphaseꢀshiftꢀdueꢀtoꢀ
thisꢀimpedanceꢀdirectlyꢀimpactsꢀtheꢀtransientꢀresponseꢀofꢀ
theꢀbuck,ꢀR1ꢀshouldꢀbeꢀchosenꢀ<125k.ꢀInꢀaddition,ꢀstrayꢀ
capacitanceꢀatꢀthisꢀpinꢀshouldꢀbeꢀminimizedꢀ(<5pF)ꢀtoꢀpre-
ventꢀexcessiveꢀphaseꢀshift.ꢀFinally,ꢀspecialꢀattentionꢀshouldꢀ
beꢀgivenꢀtoꢀanyꢀstrayꢀcapacitancesꢀthatꢀcanꢀcoupleꢀexternalꢀ
signalsꢀontoꢀtheꢀBUCKFBꢀpinꢀproducingꢀundesirableꢀoutputꢀ
ripple.ꢀForꢀoptimumꢀperformanceꢀconnectꢀtheꢀBUCKFBꢀ
pinꢀtoꢀR1ꢀandꢀR2ꢀwithꢀaꢀshortꢀPCBꢀtraceꢀandꢀminimizeꢀallꢀ
otherꢀstrayꢀcapacitanceꢀtoꢀtheꢀBUCKFBꢀpin.
Aluminumꢀelectrolyticꢀandꢀdryꢀtantalumꢀcapacitorsꢀareꢀbothꢀ
availableꢀinꢀsurfaceꢀmountꢀconfigurations.ꢀInꢀtheꢀcaseꢀofꢀ
tantalum,ꢀitꢀisꢀcriticalꢀthatꢀtheꢀcapacitorsꢀareꢀsurgeꢀtestedꢀ
forꢀuseꢀinꢀswitchingꢀpowerꢀsupplies.ꢀAnꢀexcellentꢀchoiceꢀisꢀ
theꢀAVXꢀTPSꢀseriesꢀofꢀsurfaceꢀmountꢀtantalum.ꢀTheseꢀareꢀ
speciallyꢀconstructedꢀandꢀtestedꢀforꢀlowꢀESRꢀsoꢀtheyꢀgiveꢀ
theꢀlowestꢀESRꢀforꢀaꢀgivenꢀvolume.ꢀOtherꢀcapacitorꢀtypesꢀ
includeꢀSanyoꢀPOSCAP,ꢀKemetꢀT510ꢀandꢀT495ꢀseries,ꢀandꢀ
Spragueꢀ593Dꢀandꢀ595Dꢀseries.ꢀConsultꢀtheꢀmanufacturerꢀ
forꢀotherꢀspecificꢀrecommendations.
Using Ceramic Input and Output Capacitors
Theꢀexternalꢀresistiveꢀdividerꢀisꢀconnectedꢀtoꢀtheꢀoutput,ꢀ
allowingꢀremoteꢀvoltageꢀsensingꢀasꢀshownꢀinꢀFigureꢀ6.
Highꢀvalue,ꢀlowꢀcostꢀceramicꢀcapacitorsꢀareꢀnowꢀbecomingꢀ
availableꢀinꢀsmallerꢀcaseꢀsizes.ꢀTheirꢀhighꢀrippleꢀcurrent,ꢀ
highꢀvoltageꢀrating,ꢀandꢀlowꢀESRꢀmakeꢀthemꢀidealꢀforꢀ
switchingꢀregulatorꢀapplications.ꢀSinceꢀtheꢀLTC3541-1’sꢀ
controlꢀloopꢀdoesꢀnotꢀdependꢀonꢀtheꢀoutputꢀcapacitor’sꢀESRꢀ
forꢀstableꢀoperation,ꢀceramicꢀcapacitorsꢀcanꢀbeꢀusedꢀfreelyꢀ
toꢀachieveꢀveryꢀlowꢀoutputꢀrippleꢀandꢀsmallꢀcircuitꢀsize.
Checking Transient Response
Theꢀregulatorꢀloopꢀresponseꢀcanꢀbeꢀcheckedꢀbyꢀlookingꢀ
atꢀtheꢀloadꢀtransientꢀresponse.ꢀSwitchingꢀregulatorsꢀtakeꢀ
severalꢀcyclesꢀtoꢀrespondꢀtoꢀaꢀstepꢀinꢀloadꢀcurrent.ꢀWhenꢀ
aꢀloadꢀstepꢀoccurs,ꢀV ꢀimmediatelyꢀshiftsꢀbyꢀanꢀamountꢀ
OUT
However,ꢀcareꢀmustꢀbeꢀtakenꢀwhenꢀceramicꢀcapacitorsꢀ
areꢀusedꢀatꢀtheꢀinputꢀandꢀtheꢀoutput.ꢀWhenꢀaꢀceramicꢀ
capacitorꢀisꢀusedꢀatꢀtheꢀinputꢀandꢀtheꢀpowerꢀisꢀsuppliedꢀ
byꢀaꢀwallꢀadapterꢀthroughꢀlongꢀwires,ꢀaꢀloadꢀstepꢀatꢀtheꢀ
equalꢀtoꢀ(ΔI
ꢀ•ꢀESR),ꢀwhereꢀESRꢀisꢀtheꢀeffectiveꢀseriesꢀ
LOAD
0.8V ≤ V
≤ 5V
OUT
R2
BUcKFB
LTc3541-1
GND
outputꢀcanꢀinduceꢀringingꢀatꢀtheꢀinput,ꢀV .ꢀAtꢀbest,ꢀthisꢀ
IN
R1
ringingꢀcanꢀcoupleꢀtoꢀtheꢀoutputꢀandꢀbeꢀmistakenꢀasꢀloopꢀ
instability.ꢀAtꢀworst,ꢀaꢀsuddenꢀinrushꢀofꢀcurrentꢀthroughꢀ
35411 F06
theꢀlongꢀwiresꢀcanꢀpotentiallyꢀcauseꢀaꢀvoltageꢀspikeꢀatꢀV ,ꢀ
IN
Figure 6. Setting the LTC3541-1 Output Voltage
largeꢀenoughꢀtoꢀdamageꢀtheꢀpart.
35411fa
ꢀꢁ
LTC3541-1
U U
W U
APPLICATIO S I FOR ATIO
resistanceꢀofꢀC .ꢀΔI
ꢀalsoꢀbeginsꢀtoꢀchargeꢀorꢀdis-
OUT
LOAD
R2
R1
LV
V
= 0.4V 1 +
OUT
OUT
(
)
chargeꢀC ,ꢀwhichꢀgeneratesꢀaꢀfeedbackꢀerrorꢀsignal.ꢀTheꢀ
OUT
R2
R1
LTc3541-1
LFB
regulatorꢀloopꢀthenꢀactsꢀtoꢀreturnꢀV ꢀtoꢀitsꢀsteady-stateꢀ
value.ꢀDuringꢀthisꢀrecoveryꢀtimeꢀV ꢀcanꢀbeꢀmonitoredꢀ
OUT
OUT
c
OUT
forꢀovershootꢀorꢀringingꢀthatꢀwouldꢀindicateꢀaꢀstabilityꢀ
problem.ꢀForꢀaꢀdetailedꢀexplanationꢀofꢀswitchingꢀcontrolꢀ
loopꢀtheoryꢀseeꢀApplicationꢀNoteꢀ76.
GND
35411 F07
Figure 7. Programming the LTC3541-1
Aꢀsecond,ꢀmoreꢀsevereꢀtransientꢀisꢀcausedꢀbyꢀswitchingꢀ
inꢀloadsꢀwithꢀlargeꢀ(>1µF)ꢀsupplyꢀbypassꢀcapacitors.ꢀTheꢀ
dischargedꢀbypassꢀcapacitorsꢀareꢀeffectivelyꢀputꢀinꢀparal-
forꢀtheꢀlinearꢀregulator.ꢀToꢀcalculateꢀtheꢀchangeꢀreferredꢀ
toꢀtheꢀoutputꢀsimplyꢀmultiplyꢀbyꢀtheꢀgainꢀofꢀtheꢀfeedbackꢀ
networkꢀ(i.e.,ꢀ1ꢀ+ꢀR2/R1).ꢀForꢀexample,ꢀtoꢀprogramꢀtheꢀ
outputꢀforꢀ1.2VꢀchooseꢀR2/R1ꢀ=ꢀ2.ꢀInꢀthisꢀexample,ꢀanꢀ
outputꢀcurrentꢀchangeꢀofꢀ1mAꢀtoꢀ300mAꢀproducesꢀ1.05mVꢀ
•ꢀ(1ꢀ+ꢀ2)ꢀ=ꢀ3.15mVꢀdropꢀatꢀtheꢀoutput.
lelꢀwithꢀC ,ꢀcausingꢀaꢀrapidꢀdropꢀinꢀV .ꢀNoꢀregulatorꢀ
OUT
OUT
canꢀdeliverꢀenoughꢀcurrentꢀtoꢀpreventꢀthisꢀproblemꢀifꢀtheꢀ
loadꢀswitchꢀresistanceꢀisꢀlowꢀandꢀitꢀisꢀdrivenꢀquickly.ꢀTheꢀ
onlyꢀsolutionꢀisꢀtoꢀlimitꢀtheꢀriseꢀtimeꢀofꢀtheꢀswitchꢀdriveꢀ
soꢀ thatꢀ theꢀ loadꢀ riseꢀ timeꢀ isꢀ limitedꢀ toꢀ approximatelyꢀ
SinceꢀtheꢀLFBꢀpinꢀisꢀrelativelyꢀhighꢀimpedanceꢀ(dependingꢀ
onꢀtheꢀresistorꢀdividerꢀused),ꢀstrayꢀcapacitanceꢀatꢀthisꢀpinꢀ
shouldꢀbeꢀminimizedꢀ(<10pF)ꢀtoꢀpreventꢀphaseꢀshiftꢀinꢀtheꢀ
errorꢀamplifierꢀloop.ꢀAdditionally,ꢀspecialꢀattentionꢀshouldꢀ
beꢀgivenꢀtoꢀanyꢀstrayꢀcapacitancesꢀthatꢀcanꢀcoupleꢀexternalꢀ
signalsꢀontoꢀtheꢀLFBꢀpinꢀproducingꢀundesirableꢀoutputꢀ
ripple.ꢀForꢀoptimumꢀperformanceꢀconnectꢀtheꢀLFBꢀpinꢀtoꢀ
R1ꢀandꢀR2ꢀwithꢀaꢀshortꢀPCBꢀtraceꢀandꢀminimizeꢀallꢀotherꢀ
strayꢀcapacitanceꢀtoꢀtheꢀLFBꢀpin.
(25ꢀ•ꢀC
).ꢀThus,ꢀaꢀ10µFꢀcapacitorꢀchargingꢀtoꢀ3.3Vꢀ
LOAD
wouldꢀrequireꢀaꢀ250µsꢀriseꢀtime,ꢀlimitingꢀtheꢀchargingꢀ
currentꢀtoꢀaboutꢀ130mA.
VLDO/LINEAR REGULATOR
Adjustable Output Voltage
TheꢀLTC3541-1ꢀLV ꢀoutputꢀvoltageꢀisꢀsetꢀbyꢀtheꢀratioꢀofꢀ
OUT
twoꢀexternalꢀresistorsꢀasꢀshownꢀinꢀFigureꢀ7.ꢀTheꢀdeviceꢀ
Output Capacitance and Transient Response
servosꢀ LV ꢀ toꢀ maintainꢀ theꢀ LFBꢀ pinꢀ voltageꢀ atꢀ 0.4Vꢀ
OUT
(referencedꢀtoꢀground).ꢀThus,ꢀtheꢀcurrentꢀinꢀR1ꢀisꢀequalꢀ
toꢀ0.4V/R1.ꢀForꢀgoodꢀtransientꢀresponse,ꢀstability,ꢀandꢀac-
curacy,ꢀtheꢀcurrentꢀinꢀR1ꢀshouldꢀbeꢀatꢀleastꢀ2µA,ꢀthusꢀtheꢀ
valueꢀofꢀR1ꢀshouldꢀbeꢀnoꢀgreaterꢀthanꢀ200k.ꢀTheꢀcurrentꢀ
inꢀR2ꢀisꢀtheꢀcurrentꢀinꢀR1ꢀplusꢀtheꢀLFBꢀpinꢀbiasꢀcurrent.ꢀ
SinceꢀtheꢀLFBꢀpinꢀbiasꢀcurrentꢀisꢀtypicallyꢀ<10nA,ꢀitꢀcanꢀbeꢀ
ignoredꢀinꢀtheꢀoutputꢀvoltageꢀcalculation.ꢀTheꢀoutputꢀvolt-
ageꢀcanꢀbeꢀcalculatedꢀusingꢀtheꢀformulaꢀinꢀFigureꢀ8.ꢀNoteꢀ
thatꢀinꢀshutdownꢀtheꢀoutputꢀisꢀturnedꢀoffꢀandꢀtheꢀdividerꢀ
TheꢀLTC3541-1ꢀisꢀdesignedꢀtoꢀbeꢀstableꢀwithꢀaꢀwideꢀrangeꢀ
ofꢀceramicꢀoutputꢀcapacitors.ꢀTheꢀESRꢀofꢀtheꢀoutputꢀcapaci-
torꢀaffectsꢀstability,ꢀmostꢀnotablyꢀwithꢀsmallꢀcapacitors.ꢀAꢀ
minimumꢀoutputꢀcapacitorꢀofꢀ2.2µFꢀwithꢀanꢀESRꢀofꢀ0.05Ωꢀ
orꢀlessꢀisꢀrecommendedꢀtoꢀensureꢀstability.ꢀTheꢀLTC3541-1ꢀ
VLDOꢀisꢀaꢀmicropowerꢀdeviceꢀandꢀoutputꢀtransientꢀresponseꢀ
willꢀbeꢀaꢀfunctionꢀofꢀoutputꢀcapacitance.ꢀLargerꢀvaluesꢀ
ofꢀoutputꢀcapacitanceꢀdecreaseꢀtheꢀpeakꢀdeviationsꢀandꢀ
provideꢀimprovedꢀtransientꢀresponseꢀforꢀlargerꢀloadꢀcurrentꢀ
changes.ꢀNoteꢀthatꢀbypassꢀcapacitorsꢀusedꢀtoꢀdecoupleꢀ
individualꢀcomponentsꢀpoweredꢀbyꢀtheꢀLTC3541-1ꢀwillꢀ
increaseꢀtheꢀeffectiveꢀoutputꢀcapacitorꢀvalue.ꢀHighꢀESRꢀ
tantalumꢀ andꢀ electrolyticꢀ capacitorsꢀ mayꢀ beꢀ used,ꢀ butꢀ
aꢀlowꢀESRꢀceramicꢀcapacitorꢀmustꢀbeꢀinꢀparallelꢀatꢀtheꢀ
output.ꢀThereꢀisꢀnoꢀminimumꢀESRꢀorꢀmaximumꢀcapacitorꢀ
sizeꢀrequirement.
currentꢀwillꢀbeꢀzeroꢀonceꢀC ꢀisꢀdischarged.
OUT
TheꢀLTC3541-1ꢀVLDOꢀandꢀlinearꢀregulatorꢀloopsꢀoperateꢀ
atꢀaꢀrelativelyꢀhighꢀgainꢀofꢀ–3.5µV/mAꢀandꢀ–3.4µV/mAꢀ
respectively,ꢀreferredꢀtoꢀtheꢀLFBꢀinput.ꢀThus,ꢀaꢀloadꢀcur-
rentꢀchangeꢀofꢀ1mAꢀtoꢀ300mAꢀproducesꢀaꢀ1.05mVꢀdropꢀ
atꢀtheꢀLFBꢀinputꢀforꢀtheꢀVLDOꢀandꢀaꢀloadꢀcurrentꢀchangeꢀ
ofꢀ1mAꢀtoꢀ30mAꢀproducesꢀaꢀ0.1mVꢀdropꢀatꢀtheꢀLFBꢀinputꢀ
35411fa
ꢀꢂ
LTC3541-1
U U
W U
APPLICATIO S I FOR ATIO
Extraꢀconsiderationꢀmustꢀbeꢀgivenꢀtoꢀtheꢀuseꢀofꢀceramicꢀ
capacitors.ꢀCeramicꢀcapacitorsꢀareꢀmanufacturedꢀwithꢀaꢀ
varietyꢀofꢀdielectrics,ꢀeachꢀwithꢀdifferentꢀbehaviorꢀacrossꢀ
temperatureꢀ andꢀ appliedꢀ voltage.ꢀ Theꢀ mostꢀ commonꢀ
dielectricsꢀusedꢀareꢀZ5U,ꢀY5V,ꢀX5RꢀandꢀX7R.ꢀTheꢀZ5Uꢀ
andꢀY5Vꢀdielectricsꢀareꢀgoodꢀforꢀprovidingꢀhighꢀcapaci-
tancesꢀinꢀaꢀsmallꢀpackage,ꢀbutꢀexhibitꢀlargeꢀvoltageꢀandꢀ
temperatureꢀcoefficientsꢀasꢀshownꢀinꢀFiguresꢀ8ꢀandꢀ9.ꢀ
Whenꢀusedꢀwithꢀaꢀ2Vꢀregulator,ꢀaꢀ1µFꢀY5Vꢀcapacitorꢀcanꢀ
loseꢀasꢀmuchꢀasꢀ75%ꢀofꢀitsꢀinitialꢀcapacitanceꢀoverꢀtheꢀ
operatingꢀtemperatureꢀrange.ꢀTheꢀX5RꢀandꢀX7Rꢀdielectricsꢀ
resultꢀinꢀmoreꢀstableꢀcharacteristicsꢀandꢀareꢀusuallyꢀmoreꢀ
suitableꢀforꢀuseꢀasꢀtheꢀoutputꢀcapacitor.ꢀTheꢀX7Rꢀtypeꢀhasꢀ
betterꢀstabilityꢀacrossꢀtemperature,ꢀwhileꢀtheꢀX5Rꢀisꢀlessꢀ
expensiveꢀandꢀisꢀavailableꢀinꢀhigherꢀvalues.ꢀInꢀallꢀcases,ꢀ
theꢀoutputꢀcapacitanceꢀshouldꢀneverꢀdropꢀbelowꢀ1µFꢀorꢀ
instabilityꢀorꢀdegradedꢀperformanceꢀmayꢀoccur.
EFFICIENCY CONSIDERATIONS
Generally,ꢀtheꢀefficiencyꢀofꢀaꢀregulatorꢀisꢀequalꢀtoꢀtheꢀout-
putꢀpowerꢀdividedꢀbyꢀtheꢀinputꢀpowerꢀtimesꢀ100%.ꢀItꢀisꢀ
oftenꢀusefulꢀtoꢀanalyzeꢀindividualꢀlossꢀtermsꢀtoꢀdetermineꢀ
whichꢀtermsꢀareꢀlimitingꢀefficiencyꢀandꢀwhatꢀifꢀanyꢀchangeꢀ
wouldꢀyieldꢀtheꢀgreatestꢀimprovement.ꢀEfficiencyꢀcanꢀbeꢀ
expressedꢀas:
ꢀ Efficiencyꢀ=ꢀ100%ꢀ–ꢀ(L1ꢀ+ꢀL2ꢀ+ꢀL3ꢀ+ꢀ...)
whereꢀL1,ꢀL2,ꢀetc.ꢀareꢀtheꢀindividualꢀlossꢀtermsꢀasꢀaꢀper-
centageꢀofꢀinputꢀpower.
20
BOTH cAPAcITORS ARE 1µF,
10V, 0603 cASE SIZE
0
Althoughꢀallꢀdissipativeꢀelementsꢀinꢀtheꢀcircuitꢀproduceꢀ
losses,ꢀthreeꢀmainꢀsourcesꢀtypicallyꢀaccountꢀforꢀtheꢀmajorityꢀ
X5R
–20
–40
ofꢀtheꢀlossesꢀinꢀtheꢀLTC3541-1ꢀcircuits:ꢀV ꢀquiescentꢀcur-
IN
2
rent,ꢀI RꢀlossesꢀandꢀlossꢀacrossꢀVLDOꢀoutputꢀdevice.ꢀWhenꢀ
Y5V
operatingꢀwithꢀbothꢀtheꢀbuckꢀandꢀVLDOꢀactiveꢀ(ENBUCKꢀ
andꢀENVLDOꢀequalꢀtoꢀlogicꢀhigh),ꢀV ꢀquiescentꢀcurrentꢀ
–60
–80
IN
lossꢀandꢀlossꢀacrossꢀtheꢀVLDOꢀoutputꢀdeviceꢀdominateꢀ
2
theꢀefficiencyꢀlossꢀatꢀlowꢀloadꢀcurrents,ꢀwhereasꢀtheꢀI Rꢀ
lossꢀandꢀlossꢀacrossꢀtheꢀVLDOꢀoutputꢀdeviceꢀdominateꢀ
theꢀefficiencyꢀlossꢀatꢀmediumꢀtoꢀhighꢀloadꢀcurrents.ꢀAtꢀ
lowꢀloadꢀcurrentsꢀwithꢀtheꢀpartꢀoperatingꢀwithꢀtheꢀlinearꢀ
regulatorꢀ(ENBUCKꢀequalꢀtoꢀlogicꢀlow,ꢀENVLDOꢀequalꢀtoꢀ
logicꢀhigh),ꢀefficiencyꢀisꢀtypicallyꢀdominatedꢀbyꢀtheꢀlossꢀ
–100
0
8
2
4
6
10
Dc BIAS VOLTAGE (V)
35411 F08
Figure 8. Change in Capacitor vs Bias Voltage
20
acrossꢀtheꢀlinearꢀregulatorꢀoutputꢀdeviceꢀandꢀV ꢀquiescentꢀ
IN
current.ꢀInꢀaꢀtypicalꢀefficiencyꢀplot,ꢀtheꢀefficiencyꢀcurveꢀatꢀ
veryꢀlowꢀloadꢀcurrentsꢀcanꢀbeꢀmisleadingꢀsinceꢀtheꢀactualꢀ
powerꢀlostꢀisꢀofꢀlittleꢀconsequence.
0
X5R
–20
Y5V
1.ꢀTheꢀV ꢀquiescentꢀcurrentꢀlossꢀinꢀtheꢀbuckꢀisꢀdueꢀtoꢀtwoꢀ
IN
–40
–60
components:ꢀtheꢀDCꢀbiasꢀcurrentꢀasꢀgivenꢀinꢀtheꢀElectricalꢀ
Characteristicsꢀandꢀtheꢀinternalꢀmainꢀswitchꢀandꢀsynchro-
nousꢀswitchꢀgateꢀchargeꢀcurrents.ꢀTheꢀgateꢀchargeꢀcurrentꢀ
resultsꢀfromꢀswitchingꢀtheꢀgateꢀcapacitanceꢀofꢀtheꢀinternalꢀ
powerꢀswitches.ꢀEachꢀtimeꢀtheꢀgateꢀisꢀswitchedꢀfromꢀhighꢀ
toꢀlowꢀtoꢀhighꢀagain,ꢀaꢀpacketꢀofꢀcharge,ꢀdQ,ꢀmovesꢀfromꢀ
–80
BOTH cAPAcITORS ARE 1µF,
10V, 0603 cASE SIZE
–100
–50
0
25
50
75
–25
TEMPERATURE (°c)
35411 F09
V ꢀtoꢀground.ꢀTheꢀresultingꢀdQ/dtꢀisꢀtheꢀcurrentꢀoutꢀofꢀ
IN
Figure 9. Change in Capacitor vs Temperature
V ꢀthatꢀisꢀtypicallyꢀlargerꢀthanꢀtheꢀDCꢀbiasꢀcurrentꢀandꢀ
IN
35411fa
ꢀꢃ
LTC3541-1
U U
W U
APPLICATIO S I FOR ATIO
Forꢀsurfaceꢀmountꢀdevices,ꢀheatꢀsinkingꢀisꢀaccomplishedꢀ
byꢀusingꢀtheꢀheat-spreadingꢀcapabilitiesꢀofꢀtheꢀPCꢀboardꢀ
andꢀitsꢀcopperꢀtraces.ꢀCopperꢀboardꢀstiffenersꢀandꢀplatedꢀ
throughꢀholesꢀcanꢀalsoꢀbeꢀusedꢀtoꢀspreadꢀtheꢀheatꢀgener-
atedꢀbyꢀpowerꢀdevices.
proportionalꢀtoꢀfrequency.ꢀBothꢀtheꢀDCꢀbiasꢀandꢀgateꢀchargeꢀ
lossesꢀareꢀproportionalꢀtoꢀV ꢀandꢀthusꢀtheirꢀeffectsꢀwillꢀ
IN
beꢀmoreꢀpronouncedꢀatꢀhigherꢀsupplyꢀvoltages.
2
2.ꢀI Rꢀlossesꢀareꢀcalculatedꢀfromꢀtheꢀresistancesꢀofꢀtheꢀ
internalꢀswitches,ꢀR ,ꢀandꢀexternalꢀinductorꢀR .ꢀInꢀcon-
SW
L
ToꢀavoidꢀtheꢀLTC3541-1ꢀexceedingꢀtheꢀmaximumꢀjunctionꢀ
temperature,ꢀsomeꢀthermalꢀanalysisꢀisꢀrequired.ꢀTheꢀgoalꢀ
ofꢀtheꢀthermalꢀanalysisꢀisꢀtoꢀdetermineꢀwhetherꢀtheꢀpowerꢀ
dissipatedꢀexceedsꢀtheꢀmaximumꢀjunctionꢀtemperatureꢀofꢀ
theꢀpart.ꢀTheꢀtemperatureꢀriseꢀisꢀgivenꢀby:
tinuousꢀmode,ꢀtheꢀaverageꢀoutputꢀcurrentꢀflowingꢀthroughꢀ
inductorꢀLꢀisꢀ“chopped”ꢀbetweenꢀtheꢀmainꢀswitchꢀandꢀtheꢀ
synchronousꢀswitch.ꢀThus,ꢀtheꢀseriesꢀresistanceꢀlookingꢀ
intoꢀtheꢀSWꢀpinꢀisꢀaꢀfunctionꢀofꢀbothꢀtopꢀandꢀbottomꢀ
MOSFETꢀR
ꢀandꢀtheꢀdutyꢀcycleꢀ(DC)ꢀasꢀfollows:
DS(ON)
ꢀ T ꢀ=ꢀP •ꢀθ
ꢀ R ꢀ=ꢀ(R
)(DC)ꢀ+ꢀ(R )(1ꢀ–ꢀDC)
DS(ON)TOP DS(ON)BOT
R
Dꢀ JA
SW
whereꢀP ꢀisꢀtheꢀpowerꢀdissipatedꢀbyꢀtheꢀregulatorꢀandꢀθ ꢀ
TheꢀR
ꢀforꢀbothꢀtheꢀtopꢀandꢀbottomꢀMOSFETsꢀcanꢀ
D
JA
DS(ON)
isꢀtheꢀthermalꢀresistanceꢀfromꢀtheꢀjunctionꢀofꢀtheꢀdieꢀtoꢀ
beꢀobtainedꢀfromꢀtheꢀTypicalꢀPerformanceꢀCharacteristicsꢀ
2
theꢀambientꢀtemperature.
curves.ꢀThus,ꢀtoꢀobtainꢀI Rꢀlosses,ꢀsimplyꢀaddꢀR ꢀtoꢀ
SW
R ꢀandꢀmultiplyꢀtheꢀresultꢀbyꢀtheꢀsquareꢀofꢀtheꢀaverageꢀ
L
Theꢀjunctionꢀtemperature,ꢀT ,ꢀisꢀgivenꢀby:
J
outputꢀcurrent.
ꢀ T ꢀ=ꢀT ꢀ+ꢀT
R
J
A
3.ꢀLossesꢀinꢀtheꢀVLDO/linearꢀregulatorꢀareꢀdueꢀtoꢀtheꢀDCꢀbiasꢀ
currentsꢀasꢀgivenꢀinꢀtheꢀElectricalꢀCharacteristicsꢀandꢀtoꢀtheꢀ
whereꢀT ꢀisꢀtheꢀambientꢀtemperature.
A
(V ꢀ–ꢀV )ꢀvoltageꢀdropꢀacrossꢀtheꢀinternalꢀoutputꢀdeviceꢀ
IN
OUT
Asꢀanꢀexample,ꢀconsiderꢀtheꢀLTC3541-1ꢀwithꢀanꢀinputꢀ
transistor.
voltageꢀV ꢀofꢀ2.9V,ꢀanꢀLV ꢀvoltageꢀofꢀ1.8V,ꢀanꢀLV ꢀ
IN
IN
OUT
voltageꢀofꢀ1.5V,ꢀaꢀloadꢀcurrentꢀofꢀ200mAꢀforꢀtheꢀbuck,ꢀ
aꢀloadꢀcurrentꢀofꢀ300mAꢀforꢀtheꢀVLDOꢀandꢀanꢀambientꢀ
temperatureꢀofꢀ85°C.ꢀFromꢀtheꢀtypicalꢀperformanceꢀgraphꢀ
OtherꢀlossesꢀwhenꢀtheꢀbuckꢀandꢀVLDOꢀareꢀinꢀoperationꢀ
(ENBUCKꢀandꢀENVLDOꢀequalꢀlogicꢀhigh),ꢀincludingꢀC ꢀ
IN
andꢀC ꢀESRꢀdissipativeꢀlossesꢀandꢀinductorꢀcoreꢀlosses,ꢀ
OUT
ofꢀswitchꢀresistance,ꢀtheꢀR
ꢀofꢀtheꢀP-channelꢀswitchꢀ
DS(ON)
generallyꢀaccountꢀforꢀlessꢀthanꢀ2%ꢀtotalꢀadditionalꢀloss.
atꢀ85°Cꢀisꢀapproximatelyꢀ0.25Ω.ꢀTheꢀR
channelꢀswitchꢀisꢀapproximatelyꢀ0.4Ω.ꢀTherefore,ꢀpowerꢀ
ofꢀtheꢀN-
DS(ON)ꢀ
THERMAL CONSIDERATIONS
dissipatedꢀbyꢀtheꢀpartꢀisꢀapproximately:
Theꢀ LTC3541-1ꢀ requiresꢀ theꢀ packageꢀ backplaneꢀ metalꢀ
(GNDꢀpin)ꢀtoꢀbeꢀwellꢀsolderedꢀtoꢀtheꢀPCꢀboard.ꢀThisꢀgivesꢀ
theꢀ DFNꢀ packageꢀ exceptionalꢀ thermalꢀ properties.ꢀ Theꢀ
powerꢀhandlingꢀcapabilityꢀofꢀtheꢀdeviceꢀwillꢀbeꢀlimitedꢀ
byꢀtheꢀmaximumꢀratedꢀjunctionꢀtemperatureꢀofꢀ125°C.ꢀ
TheꢀLTC3541-1ꢀhasꢀinternalꢀthermalꢀlimitingꢀdesignedꢀtoꢀ
protectꢀtheꢀdeviceꢀduringꢀmomentaryꢀoverloadꢀconditions.ꢀ
Forꢀcontinuousꢀnormalꢀconditions,ꢀtheꢀmaximumꢀjunctionꢀ
temperatureꢀratingꢀofꢀ125°Cꢀmustꢀnotꢀbeꢀexceeded.ꢀItꢀisꢀ
importantꢀtoꢀgiveꢀcarefulꢀconsiderationꢀtoꢀallꢀsourcesꢀofꢀ
thermalꢀresistanceꢀfromꢀjunctionꢀtoꢀambient.ꢀAdditionalꢀ
heatꢀsourcesꢀmountedꢀnearbyꢀmustꢀalsoꢀbeꢀconsidered.ꢀ
2
ꢀ P ꢀ=ꢀ(I
) ꢀ•ꢀR ꢀ+ꢀ(I
)•ꢀ
D
LOADBUCK
SW
LOADVLDO ꢀ
ꢀ ꢀ ꢀꢀꢀꢀꢀ(LV ꢀ–ꢀLV )ꢀ=ꢀ167mW
IN
OUT
Forꢀtheꢀ3mmꢀ×ꢀ3mmꢀDFNꢀpackage,ꢀtheꢀθ ꢀisꢀ43°C/W.
JA
Thus,ꢀtheꢀjunctionꢀtemperatureꢀofꢀtheꢀregulatorꢀis:
ꢀ T ꢀ=ꢀ85°Cꢀ+ꢀ(0.167)(43)ꢀ=ꢀ92°C
J
whichꢀisꢀwellꢀbelowꢀtheꢀmaximumꢀjunctionꢀtemperatureꢀ
ofꢀ125°C.
Noteꢀthatꢀatꢀhigherꢀsupplyꢀvoltages,ꢀtheꢀjunctionꢀtempera-
tureꢀisꢀlowerꢀdueꢀtoꢀreducedꢀswitchꢀresistanceꢀR
.
DS(ON)
35411fa
ꢀꢄ
LTC3541-1
U U
W U
APPLICATIO S I FOR ATIO
PC BOARD LAYOUT CHECKLIST
ingꢀupꢀtoꢀ0.3Aꢀofꢀcurrent.ꢀWithꢀthisꢀinformationꢀweꢀcanꢀ
calculateꢀLꢀusingꢀEquationꢀ2:
Whenꢀlayingꢀoutꢀtheꢀprintedꢀcircuitꢀboard,ꢀtheꢀfollowingꢀ
checklistꢀshouldꢀbeꢀusedꢀtoꢀensureꢀproperꢀoperationꢀofꢀtheꢀ
LTC3541-1.ꢀCheckꢀtheꢀfollowingꢀinꢀyourꢀlayout:
VOUT
VIN
1
f ΔI
L =
VOUT 1−
(2)
L
ꢀ
ꢀ
1.ꢀTheꢀpowerꢀtraces,ꢀconsistingꢀofꢀtheꢀGNDꢀtrace,ꢀtheꢀSWꢀ
SubstitutingꢀV ꢀ=ꢀ1.8V,ꢀV ꢀ=ꢀ3.6Vꢀ(typ),ꢀΔI ꢀ=ꢀ0.2Aꢀandꢀ
traceꢀandꢀtheꢀV ꢀtraceꢀshouldꢀbeꢀkeptꢀshort,ꢀdirectꢀandꢀ
OUT
IN
L
IN
fꢀ=ꢀ2.25MHzꢀinꢀEquationꢀ3ꢀgives:
wide.
2.ꢀDoesꢀtheꢀLFBꢀpinꢀconnectꢀdirectlyꢀtoꢀtheꢀfeedbackꢀre-
sistors?ꢀTheꢀresistiveꢀdividerꢀR1/R2ꢀmustꢀbeꢀconnectedꢀ
1.8V
2.25MHz(200mA)
1.8V
3.6V
L =
1−
= 2µH
(3)
ꢀ
ꢀ
betweenꢀtheꢀ(+)ꢀplateꢀofꢀC ꢀandꢀground.
OUT
Aꢀ2.2µHꢀinductorꢀworksꢀwellꢀforꢀthisꢀapplication.ꢀForꢀbestꢀ
efficiencyꢀchooseꢀaꢀ600mAꢀorꢀgreaterꢀinductorꢀwithꢀlessꢀ
thanꢀ0.2Ωꢀseriesꢀresistance.
3.ꢀDoesꢀtheꢀ(+)ꢀplateꢀofꢀC ꢀconnectꢀtoꢀV ꢀasꢀcloselyꢀasꢀ
IN
IN
possible?ꢀThisꢀcapacitorꢀprovidesꢀtheꢀACꢀcurrentꢀtoꢀtheꢀ
internalꢀpowerꢀMOSFETs.
C ꢀwillꢀrequireꢀanꢀRMSꢀcurrentꢀratingꢀofꢀatꢀleastꢀ0.25Aꢀ=ꢀ
IN
4.ꢀKeepꢀtheꢀswitchingꢀnode,ꢀSW,ꢀawayꢀfromꢀtheꢀsensitiveꢀ
LFBꢀnode.
I
/2ꢀatꢀtemperatureꢀ.ꢀC ꢀforꢀtheꢀbuckꢀisꢀchosenꢀ
LOAD(MAX)
OUT
asꢀ22µFꢀwithꢀanꢀESRꢀofꢀlessꢀthanꢀ0.2Ω.ꢀInꢀmostꢀcases,ꢀaꢀ
ceramicꢀcapacitorꢀwillꢀsatisfyꢀthisꢀrequirement.
5.ꢀKeepꢀtheꢀ(–)ꢀplatesꢀofꢀC ꢀandꢀC ꢀasꢀcloseꢀasꢀpos-
IN
OUT
sible.
Forꢀtheꢀfeedbackꢀresistorsꢀofꢀtheꢀbuck,ꢀchooseꢀR1ꢀ=ꢀ80k.ꢀ
R2ꢀcanꢀthenꢀbeꢀcalculatedꢀfromꢀEquationꢀ4ꢀtoꢀbe:
DESIGN EXAMPLE
V
0.8
OUT
Asꢀaꢀdesignꢀexample,ꢀassumeꢀtheꢀLTC3541-1ꢀisꢀusedꢀinꢀ
aꢀsingleꢀlithium-ionꢀbatteryꢀpoweredꢀcellularꢀphoneꢀap-
R2=
−1 R1=100k
(4)
ꢀ
ꢀ
plication.ꢀTheꢀV ꢀwillꢀbeꢀoperatingꢀfromꢀaꢀmaximumꢀofꢀ
IN
ForꢀtheꢀfeedbackꢀresistorsꢀofꢀtheꢀVLDO,ꢀchooseꢀR1ꢀ=ꢀ200k.ꢀ
R2ꢀcanꢀthenꢀbeꢀcalculatedꢀfromꢀEquationꢀ5ꢀtoꢀbe:
4.2Vꢀdownꢀtoꢀaboutꢀ3V.ꢀTheꢀloadꢀcurrentꢀrequirementꢀisꢀ
aꢀmaximumꢀofꢀ0.5Aꢀforꢀtheꢀbuckꢀoutputꢀbutꢀmostꢀofꢀtheꢀ
timeꢀitꢀwillꢀbeꢀinꢀstandbyꢀmode,ꢀrequiringꢀonlyꢀ2mA.ꢀEf-
ficiencyꢀatꢀbothꢀlowꢀandꢀhighꢀloadꢀcurrentsꢀisꢀimportant.ꢀ
Theꢀoutputꢀvoltageꢀforꢀtheꢀbuckꢀisꢀ1.8V.ꢀTheꢀrequirementꢀ
forꢀtheꢀoutputꢀvoltageꢀofꢀtheꢀVLDOꢀisꢀ1.5Vꢀwhileꢀprovid-
V
OUT
R2=
−1 R1= 550k
0.4
ꢀ
C
ꢀforꢀtheꢀVLDOꢀisꢀchosenꢀasꢀ2.2µF.
OUT
35411fa
ꢀꢅ
LTC3541-1
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
3.2V TO 4.2V
V
OUT
2V/DIV
ENVLDO
MODE
GND
V
IN
LV
OUT
ENBUCK
2V/DIV
2.2µH
V
OUT1
2.5V
SW
400mA
165k
576k
LTC3541-1
V
IN
22pF
LV
LFB
IN
2V/DIV
154k
73k
V
OUT2
1.8V
BUCKFB
PGND
LV
OUT
30mA
2.2µF
10µF
3541 TA02b
4ms/DIV
I
I
= 400mA
LVOUT
VOUT
35411 TA02a
= 30mA
Dual Output with Minimal External Components Using Auto Start-Up
Sequence, Buck in Pulse Skip Mode for Low Noise Operation
V
IN
3.2V TO 4.2V
V
OUT
2V/DIV
ENVLDO
ENBUCK MODE
V
IN
LV
OUT
2V/DIV
2.2µH
V
OUT1
2.5V
GND
SW
400mA
165k
576k
LTC3541-1
V
IN
22pF
LV
IN
LFB
2V/DIV
154k
73k
V
OUT2
1.8V
BUCKFB
PGND
LV
OUT
30mA
2.2µF
3541 TA03b
10µF
4ms/DIV
I
I
= 400mA
LVOUT
VOUT
35411 TA03a
= 30mA
35411fa
ꢀꢆ
LTC3541-1
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
3.2V TO 4.2V
V
OUT
2V/DIV
ENVLDO
ENBUCK MODE
V
IN
LV
OUT
2.2µH
V
OUT1
2.5V
2V/DIV
GND
SW
200mA
165k
576k
LTC3541-1
22pF
LV
IN
LFB
V
IN
154k
73k
2V/DIV
V
OUT2
1.8V
BUCKFB
PGND
LV
OUT
300mA
2.2µF
10µF
35411 TA04b
4ms/DIV
I
I
= 200mA
LVOUT
35411 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
2.9V TO 4.2V
V
OUT
2V/DIV
V
ENVLDO
MODE
GND
IN
ENBUCK
SW
LV
OUT
2.2µH
V
OUT1
1.8V
2V/DIV
200mA
150k
412k
LTC3541-1
22pF
LV
IN
LFB
V
IN
143k
115k
2V/DIV
V
OUT2
1.5V
BUCKFB
PGND
LV
OUT
300mA
2.2µF
10µF
35411 TA05b
4ms/DIV
I
I
= 200mA
LVOUT
VOUT
35411 TA05a
= 30mA
35411fa
ꢀꢇ
LTC3541-1
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
35411fa
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
LTC3541-1
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
LTC3541-2
LTC3541-3
LTC3547
TripleꢀOutputꢀStep-DownꢀConverterꢀ1AꢀOutputꢀBuck,ꢀ V :ꢀ2.7Vꢀtoꢀ5.5V,ꢀV ꢀBuckꢀ=ꢀ0.8V,ꢀV
ꢀVLDOꢀ=ꢀ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,ꢀꢀ
OUT(MIN)
IN
OUT(MIN)
3mmꢀ×ꢀ3mmꢀ10-PinꢀDFNꢀPackage
V :ꢀ2.9Vꢀtoꢀ5.5V,ꢀV ꢀ=ꢀ1.875V,ꢀV ꢀ=ꢀ1.5V,ꢀ3mmꢀ×ꢀ3mmꢀ
OUT(VLDO)
HighꢀEfficiencyꢀBuckꢀplusꢀVLDOꢀRegulator
HighꢀEfficiencyꢀBuckꢀplusꢀVLDOꢀRegulator
IN
OUT(BUCK)
10-PinꢀDFNꢀPackage
V :ꢀ3Vꢀtoꢀ5.5V,ꢀV
ꢀ=ꢀ1.8V,ꢀV ꢀ=ꢀ1.575V,ꢀ3mmꢀ×ꢀ3mmꢀꢀ
OUT(VLDO)
IN
OUT(BUCK)
10-PinꢀDFNꢀPackage
Dualꢀ300mAꢀ(I ),ꢀ2.25MHz,ꢀSynchronousꢀꢀ
95%ꢀEfficiency,ꢀV :ꢀ2.5Vꢀtoꢀ5.5V,ꢀV
ꢀ=ꢀ0.6V,ꢀI ꢀ=ꢀ40µA,ꢀI ꢀ<ꢀ1µA,ꢀ
Q SD
OUT
IN
OUT(MIN)
Step-DownꢀDC/DCꢀConverter
8-PinꢀDFNꢀPackage
LTC3548/LTC3548-1ꢀ Dualꢀ800mA/400mAꢀ(I ),ꢀ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.ꢀ
35411fa
LT 0407 REV A • PRINTED IN USA
LinearTechnology Corporation
1630 Mꢀcarthy Blvd., Milpitas, cA 95035-7417
ꢁ0
●
●
LINEAR TECHNOLOGY CORPORATION 2007
(408)432-1900 FAX: (408) 434-0507 www.linear.ꢀom
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