参数资料
型号: LTC4266CGW#TRPBF
厂商: LINEAR TECHNOLOGY CORP
元件分类: 电源管理
英文描述: POWER SUPPLY MANAGEMENT CKT, PDSO36
封装: 0.300 INCH, LEAD FREE, PLASTIC, SSOP-36
文件页数: 11/30页
文件大小: 414K
代理商: LTC4266CGW#TRPBF
LTC4266
4266fa
ApplicAtions inForMAtion
capacitance(>10μF)asthedetectionsignature.Notethat
PDsinthisrangeofcapacitancearedefinedasinvalid,so
aPSEthatdetectslegacyPDsistechnicallynoncompliant
withtheIEEEspec.
TheLTC4266canbeconfiguredtodetectthistypeoflegacy
PD.Legacydetectionisdisabledbydefault,butcanbe
manuallyenabledonaper-portbasis.Whenenabled,the
portwillreportdetectgoodwhenitseeseitheravalidIEEE
PDorahigh-capacitancelegacyPD.Withlegacymode
disabled,onlyvalidIEEEPDswillberecognized.
CLASSIFICATION
802.3afClassification
APDcanoptionallypresentaclassificationsignatureto
thePSEtoindicatethemaximumpoweritwilldrawwhile
operating.TheIEEEspecificationdefinesthissignatureas
aconstantcurrentdrawwhenthePSEportvoltageisinthe
VCLASSrange(between15.5Vand20.5V),withthecurrent
levelindicatingoneof5possiblePDclasses.Figure14
showsatypicalPDloadline,startingwiththeslopeof
the25ksignatureresistorbelow10V,thentransitioning
totheclassificationsignaturecurrent(inthiscase,Class
3)intheVCLASSrange.Table3showsthepossibleclas-
sificationvalues.
Table3.ClassificationValues
CLASS
RESULT
Class0
NoClassSignaturePresent;TreatLikeClass3
Class1
3W
Class2
7W
Class3
13W
Class4
25.5W(Type2)
Ifclassificationisenabled,theportwillclassifythePD
immediatelyafterasuccessfuldetectioncycleinsemi-auto
orautomodes,orwhencommandedtoinmanualmode.It
measuresthePDclassificationsignaturebyapplying18V
for12ms(bothvaluestypical)totheportviatheOUT
npin
andmeasuringtheresultingcurrent;itthenreportsthe
discoveredclassintheportstatusregister.IftheLTC4266
wasresetwiththeAUTOpinhighandtheportisinauto
mode,itwilladditionallyusetheclassificationresulttoset
theICUTandILIMthresholds.SeethePower-OnResetand
theAUTO/MIDPinsectionformoreinformation.
Theclassificationcircuitryisdisabledwhentheportis
initiallypoweredupwiththeAUTOpinlow,inshutdown
mode, or when the corresponding class enable bit is
cleared.
802.3at2-EventClassification
The802.3atspecdefinestwomethodsofclassifyinga
Type2PD.
OnemethodaddsextrafieldstotheEthernetLLDPdata
protocol;althoughtheLTC4266iscompatiblewiththis
classification method, it cannot perform classification
directly since it doesn’t have access to the data path.
LLDPclassificationrequiresthePSEtopowerthePDas
astandard802.3af(Type1)device.Itthenwaitsforthe
hosttoperformLLDPcommunicationwiththePDand
updatethePSEportdata.TheLTC4266supportschang-
ingtheILIMandICUTlevelsonthefly,allowingthehost
tocompleteLLDPclassification.
Thesecond802.3atclassificationmethod,knownas2-
eventclassificationorping-pong,isfullysupportedbythe
LTC4266.AType2PDthatisrequestingmorethan13W
willindicateClass4duringnormal802.3afclassification.
IftheLTC4266seesClass4,itforcestheporttoaspeci-
fiedlowervoltage(calledthemarkvoltage,typically9V),
pausesbriefly,andthenre-runsclassificationtoverifythe
Class4reading(Figure1).Italsosetsabitinthehigh
VOLTAGE (VCLASS)
0
CURRENT
(mA)
60
50
40
30
20
10
0
5
10
15
20
4266 F13
25
TYPICAL
CLASS 3
PD LOAD
LINE
48mA
33mA
PSE LOAD LINE
23mA
14.5mA
6.5mA
CLASS 4
CLASS 2
CLASS 1
CLASS 0
CLASS 3
OVER
CURRENT
Figure13.PDClassification
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