HT7L2102 datasheet(6/11 Pages) HOLTEK

6 / 11 page

Rev. 1.00

November 4, 2011

HT7L2102

Under Voltage Lockout (UVLO)

AnUVLOcomparatorisimplementedintoensure

thatthedeviceisfullyfunctionalbeforetheoutput

stageisenabled.AsshowninFig.10,hysteresis

isprovidedtopreventthePWMControllerfrom

shutting down during any voltage dips which

mightoccurduringstartup.Theturn-onandturn-

off threshold levels are set at 16.0V and 10.0V,

respectively.

Figure 10. UVLO Scheme and Start-Up Current

Current Sense and Leading-Edge

Blanking (LEB)

ALeading-EdgeBlankingSchemeisintegratedin

thedevicetopreventfalsetriggeringduetofeedback

currentspikeswhichmayappearontheCSpin,

furthereliminatingtheneedforanR-Cfilterwhich

isalwaysarequirementintraditionalcurrentmode

PWMControllerapplications.

Figure 11. LEB with R-C Filter Removed

Internal Slope-Compensation

An important issue with current mode control

structures is instability due to Sub-Harmonic

OscillationwhentheDuty-Cycle>50%.Toprevent

thisproblemfromoccurring,aSlope-Compensation

function is always necessary. In traditional

currentmodePWMControllerapplication,many

externalcomponentsarenecessarytoimplement

aSlope-Compensationfunction.Howeverinthe

HT7L2102, the internal Slope-Compensation

eliminatestheneedfortheseexternalcomponents

resultinginasimplifiedtheapplicationcircuitdesign.

Short-Circuit Protection (SCP) and

Over-Load Protection (OLP)

Toprotectallthedevicesinasystemfrombeing

damagedduetooverloadorshortcircuitconditions,

asmartSCPfunctionisimplementedinthedevice.

Herethefeedbacksystemwillforcethevoltageloop

tomovetowardasaturationvalueandthenpullup

thevoltageontheCOMPpin.WhenevertheVCOMP

increasestotheSCPthresholdof4.7Vandremains

thereforlongerthan40mS,theprotectionschemewill

activateandthenturnoffthegateoutputtostopthe

powercircuitswitching.Byusingsuchaprotection

mechanism,theaverageinputpowercanbereduced

toaverylowlevelsothatcomponenttemperatureand

stresscanbecontrolledwithinsafeoperatinglevels.

Figure 12. SCP Function Behavior

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