参数资料
型号: LTC3677EUFF-3#PBF
厂商: LINEAR TECHNOLOGY CORP
元件分类: 电源管理
英文描述: POWER SUPPLY MANAGEMENT CKT, PQCC44
封装: 7 X 4 MM, 0.75 MM HEIGHT, LEAD FREE, PLASTIC, QFN-44
文件页数: 21/44页
文件大小: 4112K
代理商: LTC3677EUFF-3#PBF
LTC3677-3
36773f
operaTion
ThepowergoodstatusbitsofLDO1andLDO2areavail-
ableinI2Cthroughtheread-backregistersPGLDO[1]and
PGLDO[2]forLDO1andLDO2respectively.Thepower
goodcomparatorsforbothLDOsaresampledwhenthe
I2CportreceivesthecorrectI2Creadaddress.
Figure7showstheLDOapplicationcircuit.Thefull-scale
outputvoltageforeachLDOisprogrammedusingaresistor
dividerfromtheLDOoutput(LDO1orLDO2)connected
tothefeedbackpins(LDO1_FBorLDO2_FB)suchthat:
V
R
LDOx =
+
0 8
1
2
1
.
Forstability,eachLDOoutputmustbebypassedtoground
withaminimum1μFceramiccapacitor(COUT).
step-downswitchingregulatorsalsoincludesoft-startto
limitinrushcurrentwhenpoweringon,short-circuitcur-
rentprotection,andswitchnodeslewlimitingcircuitryto
reduceEMIradiation.Noexternalcompensationcompo-
nentsarerequiredfortheswitchingregulators.Switching
regulators1and2(Buck1andBuck2)aresequencedup
anddowntogetherthroughthepushbuttoninterface(see
thePushbuttonInterfacesectionformoreinformation),
whileBuck3hasanindividualenablepin(EN3)thatisac-
tivewhenthepushbuttonisinthepower-uporpower-on
states.Buck3isdisabledinthepowerdownandpoweroff
states.Itisrecommendedthatthestep-downswitching
regulatorinputsupplies(VIN12andVIN3)beconnectedtothe
systemsupplypin(VOUT).Thisisrecommendedbecause
theundervoltagelockoutcircuitontheVOUTpin(VOUT
UVLO)disablesthestep-downswitchingregulatorswhen
theVOUTvoltagedropsbelowtheVOUTUVLOthreshold.If
drivingthestep-downswitchingregulatorinputsupplies
from a voltage other than VOUT the regulators should
notbeoperatedoutsidethespecifiedoperatingrangeas
operationisnotguaranteedbeyondthisrange.
Output Voltage Programming
Figure8 shows the step-down switching regulator ap-
plication circuit. The full-scale output voltage for each
step-downswitchingregulatorisprogrammedusinga
resistordividerfromthestep-downswitchingregulator
output connected to the feedback pins (FB1, FB2 and
FB3)suchthat:
V
R
OUTx =
+
0 8
1
2
1
.
Figure 7. LDO Application Circuit
0.8V
R1
LDOx
OUTPUT
COUT
R2
36773 F07
MP
VINLDOx
GND
LDOx_FB
1
0
LDOx
LDOxEN
Figure 8. Step-Down Switching Regulator Application Circuit
0.8V
R1
L
VOUTx
COUT
CFB
R2
36773 F08
MP
MN
EN
MODE
SLEW
VIN
GND
FBx
SWx
PWM
CONTROL
STEP-DOWN SWITCHING REGULATOR OPERATION
Introduction
TheLTC3677-3includesthree2.25MHzconstant-frequency
currentmodestep-downswitchingregulatorsproviding
500mA,500mAand800mAeach.Allstep-downswitch-
ingregulatorscanbeprogrammedforaminimumoutput
voltageof0.8Vandcanbeusedtopoweramicrocontroller
core,microcontrollerI/O,memoryorotherlogiccircuitry.
Allstep-downswitchingregulatorssupport100%duty
cycleoperation(lowdropoutmode)whentheinputvolt-
agedropsveryclosetotheoutputvoltageandarealso
capableofBurstModeoperationforhighestefficiencies
atlightloads.BurstModeoperationisindividuallyselect-
ableforeachstep-downswitchingregulatorthroughthe
I2CregisterbitsBK1BRST,BK2BRSTandBK3BRST.The
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