www.德州仪器.com
detaileddescription(持续)
OUTPUTDISCHARGECONTROL
CURRENTPROTECTION
V
trip
(mv)
R
trip
(k
)
10 (
一个)
(2)
I
ocl
V
trip
R
ds(在)
I
波纹
2
V
trip
R
ds(在)
1
2
L
ƒ
V
在
V
输出
V
输出
V
在
(3)
在/下面-voltageprotection
UVLOPROTECTION
THERMALSHUTDOWN
TPS51124
SLVS616A–NOVEMBER2005–REVISEDNOVEMBER2005
tps51124dischargestheoutputwhenenxislow,orthecontrolleristurnedoffbytheprotectionfunctions
(ovp,uvp,uvlo,andthermalshutdown).tps51124dischargesoutputsusinganinternal,10-
Ω
场效应晶体管
whichisconnectedtovoxandpgndx.theexternallow-sidemosfetisnotturnedonfortheoutputdischarge
operationtoavoidthepossibilityofcausingnegativevoltageattheoutput.outputdischargetimeconstantisa
functionoftheoutputcapacitanceandtheresistanceoftheinternaldischargemosfet.thisdischargeensures
那,onrestart,theregulatedvoltagealwaysstartsfromzerovolts.incaseasmpsisrestartedbeforedischarge
completion,dischargeisterminatedandtheswitchingresumesafterthereferencelevel,rampedupbyan
internaldac,comesbacktotheremainingoutputvoltage.
tps51124hascycle-用-cycleover-currentlimitingcontrol.theinductorcurrentismonitoredduringthe
止
stateandthecontrollerkeepsthe
止
stateduringtheinductorcurrentislargerthantheover-currenttriplevel.
inordertoprovidebothgoodaccuracyandcosteffectivesolution,tps51124supportstemperature
compensatedMOSFETR
ds(在)
感觉到.tripxpinshouldbeconnectedtogndthroughthetripvoltagesetting
电阻,r
trip
.tripxterminalsources10-
µ
AItripcurrentandthetriplevelissettotheOCLtripvoltageV
trip
作
在下.
thetriplevelshouldbeintherangeof30mvto200mvoveralloperationaltemperatures.theinductorcurrent
ismonitoredbythevoltagebetweenPGNDxpinandLLxpinsothatLLxpinshouldbeconnectedtothedrain
terminalofthelow-sidemosfet.itriphas4200ppm/
°
Ctemperatureslopetocompensatethetemperature
dependencyoftheR
ds(在)
.pgndxisusedasthepositivecurrentsensingnodesothatpgndxshouldbe
connectedtothesourceterminalofthelow-sidemosfet.asthecomparisonisdoneduringthe
止
状态,v
trip
setsthevalleyleveloftheinductorcurrent.因此,theloadcurrentatover-currentthreshold,i
ocl
,canbe
calculatedasfollows;
inanover-currentcondition,thecurrenttotheloadexceedsthecurrenttotheoutputcapacitor;因此,theoutput
voltagetendstofalloff(droop).eventually,itendsupcrossingtheunder-voltageprotectionthresholdandshuts
向下.
tps51124monitorsaresistordividedfeedbackvoltagetodetectoverandundervoltage.whenthefeedback
voltagebecomeshigherthan115%ofthetargetvoltage,theovpcomparatoroutputgoeshighandthecircuit
latchesasthehigh-sidemosfetdriveroffandthelow-sidemosfetdriveron.
也,thetps51124monitorsvoxvoltagedirectlyandifitbecomesgreaterthan5.75v,thetps51124turnsoff
thetopmosfetdriver,andshutsoffbothdriversoftheotherchannel.
whenthefeedbackvoltagebecomeslowerthan70%ofthetargetvoltage,theuvpcomparatoroutputgoes
highandaninternaluvpdelaycounterbeginscounting.after32
µ
s,tps51124latchesoffbothtopand
bottommosfetdrivers,andshutsoffbothdriversoftheotherchannel.thisfunctionisenabledafter1.7times
软-startdelaytime,approximately2ms,toensurestart-upproperly.
tps51124hasv5filtunder-voltagelock-outprotection(uvlo).whenthev5filtvoltageislowerthanuvlo
thresholdvoltage,thetps51124isshutoff.thisisnon-latchprotection.
tps51124monitorsitsowntemperature.ifthetemperatureexceedsthethresholdvalue(typically160
°
c),这
switchersareshutoffasbothdrvhanddrvlatlow;theoutputdischargefunctionisenabled.tps51124is
shutoff.thisisnon-latchprotection.
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