PR8275
High Voltage Start-Up PWM Controller
latchꢀisꢀreleasedꢀifꢀtheꢀ2ndꢀUVLO(off)ꢀpointꢀ
isꢀcountedꢀthenꢀtheꢀoutputꢀisꢀrecoveryꢀtoꢀ
switchingꢀagain.ꢀByꢀusingꢀsuchꢀprotectionꢀ
mechanism,ꢀtheꢀaverageꢀinputꢀpowerꢀcanꢀ
beꢀreducedꢀtoꢀveryꢀlowꢀlevelꢀsoꢀthatꢀtheꢀ
componentꢀtemperatureꢀandꢀstressꢀ
canꢀbeꢀcontrolledꢀwithinꢀtheꢀsafeꢀoperatingꢀ
area.
Fig.7
OVP (Over Voltage Protection) on Vcc
Theꢀ Vgsꢀ ratingsꢀ ofꢀ theꢀ nowadaysꢀ powerꢀ
workingꢀasꢀaꢀhiccupꢀmode.ꢀFigureꢀ8ꢀshowsꢀ
itsꢀ operation.ꢀ Onꢀ theꢀ otherꢀ hand,ꢀ ifꢀ theꢀ
OVPꢀ conditionꢀ isꢀ removed,ꢀ theꢀ Vccꢀ levelꢀ
willꢀgetꢀbackꢀtoꢀnormalꢀlevelꢀandꢀtheꢀoutputꢀ
isꢀ automaticallyꢀ returnedꢀ toꢀ theꢀ normalꢀ
operation.
MOSFETsꢀ areꢀ mostꢀ withꢀ maximumꢀ 30V.ꢀ
ToꢀpreventꢀtheꢀVgsꢀfromꢀtheꢀfaultꢀcondition,ꢀ
PR8275ꢀisꢀimplementedꢀanꢀOVPꢀfunctionꢀ
onꢀ Vcc.ꢀ Wheneverꢀ theꢀ Vccꢀ voltageꢀ isꢀ
higherꢀthanꢀtheꢀOVPꢀthresholdꢀvoltage,ꢀtheꢀ
outputꢀ gateꢀ driveꢀ circuitꢀwillꢀ beꢀ shutdownꢀ
simultaneousꢀthusꢀtoꢀstopꢀtheꢀswitchingꢀofꢀ
theꢀ powerꢀ MOSFETꢀ untilꢀ theꢀ nextꢀ
UVLO(on). ꢀ
Theꢀ Vccꢀ OVPꢀ functionꢀ inꢀ PR8275ꢀ isꢀ anꢀ
autoꢁrecoveryꢀ typeꢀ protection.ꢀIfꢀtheꢀOVPꢀ
condition,ꢀusuallyꢀcausedꢀbyꢀtheꢀfeedbackꢀ
loopꢀopened,ꢀisꢀnotꢀreleased,ꢀtheꢀVccꢀwillꢀ
trippedꢀ theꢀ OVPꢀ levelꢀ againꢀ andꢀ
reꢁshutdownꢀ theꢀ output.ꢀ Theꢀ Vccꢀ isꢀ
ꢀ
Fig.8ꢀ
Fault Protection
Aꢀ lotꢀ ofꢀ protectionꢀ featuresꢀ haveꢀ beenꢀ
theꢀgateꢀ outputꢀ willꢀ beꢀ offꢀimmediatelyꢀ toꢀ
protectꢀtheꢀpowerꢀcircuitꢀꢁꢁꢁꢀ
1.ꢀ RTꢀpinꢀshortꢀtoꢀgroundꢀ
2.ꢀ RTꢀpinꢀfloatingꢀ
implementedꢀinꢀtheꢀPR8275ꢀtoꢀpreventꢀtheꢀ
powerꢀ supplyꢀ orꢀ adapterꢀ fromꢀ beingꢀ
damagedꢀcausedꢀbyꢀsingleꢀfaultꢀconditionꢀ
onꢀtheꢀopenꢀorꢀshortꢀconditionꢀonꢀtheꢀpinꢀofꢀ
PR8275.ꢀUnderꢀtheꢀconditionsꢀlistedꢀbelow,ꢀ
ꢀ
3.ꢀ CSꢀpinꢀfloatingꢀ
Pull-Low Resistor on the Gate Pin of MOSFET
Inꢀ PR8275,ꢀ anꢀ antiꢁfloatingꢀ resistorꢀ isꢀ
implementedꢀ onꢀ theꢀ OUTꢀ pinꢀ toꢀ preventꢀ
V1.0
8/10
ETC [ ETC ]
