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参数资料
| 型号： | LTC4266IUHF#PBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 电源管理 |
| 英文描述： | POWER SUPPLY MANAGEMENT CKT, PQCC38 |
| 封装： | 5 X 7 MM, LEAD FREE, PLASTIC, MO-220WHKD, QFN-38 |
| 文件页数： | 10/30页 |
| 文件大小： | 414K |
| 代理商： | LTC4266IUHF#PBF |
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LTC4266
4266fa
ApplicAtions inForMAtion
4-PointDetection
TheLTC4266usesa4-pointdetectionmethodtodiscover
PDs.False-positivedetectionsareminimizedbycheck-
ingforsignatureresistancewithbothforced-currentand
forced-voltagemeasurements.Initially,twotestcurrents
areforcedontotheport(viatheOUTnpin)andtheresulting
voltagesaremeasured.Thedetectioncircuitrysubtracts
thetwoV-Ipointstodeterminetheresistiveslopewhile
removingoffsetcausedbyseriesdiodesorleakageat
theport(seeFigure12).Iftheforced-currentdetection
yieldsavalidsignatureresistance,twotestvoltagesare
thenforcedontotheportandtheresultingcurrentsare
measured and subtracted. Both methods must report
validresistancesfortheporttoreportavaliddetection.
PDsignatureresistancesbetween17kand29k(typically)
aredetectedasvalidandreportedasDetectGoodinthe
correspondingPortStatusregister.Valuesoutsidethis
range,includingopenandshortcircuits,arealsoreported.
Iftheportmeasureslessthan1Vatthefirstforced-current
test,thedetectioncyclewillabortandShortCircuitwillbe
reported.Table2showsthepossibledetectionresults.
Table2.DetectionStatus
MEASUREDPDSIGNATURE
DETECTIONRESULT
IncompleteorNotYetTested
DetectStatusUnknown
<2.4k
ShortCircuit
Capacitance>2.7F
CPDtooHigh
2.4k<RPD<17k
RSIGtooLow
17k<RPD<29k
DetectGood
>29k
RSIGtooHigh
>50k
OpenCircuit
Voltage>10V
PortVoltageOutsideDetectRange
OperatingModes
Theport’soperatingmodedetermineswhentheLTC4266
runs a detection cycle. In manual mode, the port will
idleuntilthehostordersadetectcycle.Itwillthenrun
detection,reporttheresults,andreturntoidletowaitfor
anothercommand.
Insemi-automode,theLTC4266autonomouslypollsa
portforPDs,butitwillnotapplypoweruntilcommanded
todosobythehost.Theportstatusregisterisupdated
attheendofeachdetectioncycle.Ifavalidsignature
resistanceisdetectedandclassificationisenabled,the
portwillclassifythePDandreportthatresultaswell.
Theportwillthenwaitforatleast100ms(or2secondsif
midspanmodeisenabled),andwillrepeatthedetection
cycletoensurethatthedataintheportstatusregisteris
up-to-date.
Iftheportisinsemi-automodeandhighpoweropera-
tionisenabled,theportwillnotturnoninresponseto
apower-oncommandunlessthecurrentdetectresultis
detectgood.AnyotherdetectresultwillgenerateatSTART
faultifapower-oncommandisreceived.Iftheportisnot
inhighpowermode,itwillignorethedetectionresultand
applypowerwhencommanded,maintainingbackwards
compatibilitywiththeLTC4259A.
Behaviorinautomodeissimilartosemi-auto;however,
afterdetectgoodisreportedandtheportisclassified(if
classificationisenabled),itisautomaticallypoweredon
withoutfurtherintervention.Instandalonemode,theICUT
andILIMthresholdsareautomaticallysetinautomode;
see the power-on Reset and the AUTO Pin section for
moreinformation.
Thesignaturedetectioncircuitryisdisabledwhentheport
isinitiallypoweredupwiththeAUTOpinlow,inshutdown
mode, or when the corresponding detect enable bit is
cleared.
DetectionofLegacyPDs
Proprietary PDs that predate the original IEEE 802.3af
standardarecommonlyreferredtotodayaslegacyde-
vices.OnetypeoflegacyPDusesalargecommonmode
Figure12.PDDetection
FIRST
DETECTION
POINT
SECOND
DETECTION
POINT
VALID PD
25k SLOPE
275
165
CURRENT
(A)
0V-2V
OFFSET
VOLTAGE
4266 F12
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