HT7A6005 datasheet(5/11 Pages) HOLTEK

5 / 11 page

Rev. 1.10

July 17, 2013

HT7A6005

Application Information

Operation Overview

TheHT7A6005isalowpower,widetemperature

rangegeneralpurposecurrentmodePWMController.

Thedeviceisdesignedtorequireaminimumof

external components for different power circuit

topologiessuchasPrimary-SideFeedbackFlyback

andDC-DCBuck/Boost.Thedevicecanbeusedfor

LEDdrivingapplicationssuchasLEDbacklights

andLEDlighting.TomeetLEDconstantcurrent

requirements,thedevicecanmaintainalowcurrent

toleranceof±1%forLEDdrivingapplications.

Under Voltage Lockout (UVLO)

AUVLOcomparatorisprovidedtoensurethatthe

deviceisfullyfunctionalbeforetheoutputstageis

enabled.AsshowninFigure5,hysteresisisprovided

topreventthePWMControllerfromshuttingdown

duringanyvoltagedipswhichmightoccurduringthe

startupprocess.Theturn-onandturn-offthreshold

levelsaresetat8.4Vand7.6V,respectively.

Figure 5. UVLO Scheme and Start-Up Current

Current Sense and Leading-Edge

Blanking (LEB)

For Isolation Flyback applications, a Leading-

EdgeBlankingSchemeisnecessary.ALeading-

EdgeBlankingSchemeisintegratedinthedeviceto

preventfalsetriggeringduetofeedbackcurrentspikes

whichmayappearontheCSpin.Thiseliminates

theneedfortheusualR-Cfilterwhichisnormallya

requirementintypicalcurrentmodePWMController

applications.

HT7A6005

350ns

Blank Time

removed

GND

VREF

0.1uF

10K

Figure 6. LEB with R-C Filter Removed

Internal Slope-Compensation

An important issue with current mode control

schemesisinstabilityduetosub-harmonicoscillation

whentheDuty-Cycle>50%.Topreventthisproblem

from occurring,a Slope-Compensationfunction

isalwaysnecessary.Intraditionalcurrentmode

controllerapplications,manyexternalcomponents

arenecessarytoimplementaSlope-Compensation

function.HoweverintheHT7A6005theinternal

Slope-Compensationfunctioneliminatestheneedfor

theseexternalcomponentsresultinginasimplified

applicationcircuitdesign.

Oscillator Frequency Tuning

Bychoosinganappropriatevalueofexternalresistor

betweentheRTPinandGND,asuitableoperating

frequencycanbegenerated.Therelationshipbetween

theRTvalueandtheoperatingfrequencyisprovided

inFigure7.

Figure 7. RT Resistor Value vs. Operating Frequency

HT7A6005 Datasheet(PDF) 5 Page - Holtek Semiconductor Inc

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