SA60U

5

P r o d u c t I n n o v a t i o n F r o m

SA60

GENERAL

PleasereadApplicationNote30on"PWMBasics".RefertoApplicationNote1"GeneralOperatingConsiderations"

forhelpfulinformationregardingpowersupplies,heatsinkingandmounting.Visitwww.Cirrus.comfordesigntools

thathelpautomatepwmfilterdesign;heatsinkselection;ApexPrecisionPower’scompleteApplicationNotesli-

brary;TechnicalSeminarWorkbook;andEvaluationKits.

PWM OSCILLATOR – INTERNAL OR ExTERNAL

TheSA60containsaninternalPWMoscillatorwhosefrequencyisdeterminedbyanexternalcapacitorconnected

betweenpin1andpin2.Maximumfrequencyis125kHz.TheusermayalsodisregardtheinternalPWMoscillator

andsupplytheSA60withanexternalTTLpulsegeneratorupto250KHZ.

PIN DESCRIPTION

suppliesforthehighsidedriversarederivedfromthisvoltage.

onthispinislimitedto+80VbythedriveIC.TheMOSFETSareratedat100volts.

ISENSE A & B-Thesearetiedtopowergnddirectlyorthroughsenseresistors.

ANALOG GND-isthereferencefortheinternalPWMoscillator.Connectthispintopin6.ConnectlowsideofVcc

supplyandanyothersupplyusedtogenerateanaloginputsignalstoANALOGGND.

ANALOG INPUT-isananaloginputforcontrollingthePWMpulsewidthofthebridge.AvoltagehigherthanVcc/2

willproducegreaterthan50%dutycyclepulsesoutofBOUT.AvoltagelowerthanVcc/2willproducegreater

than50%dutycyclepulsesoutofAOUT.Ifusinginthedigitalmode,biasthispointat1/2thelogichighlevel.

DISABLE-Istheconnectionfordisablingall4outputswitches.DISABLEhighoverridesallotherinputs.When

takenlow,everythingfunctionsnormally.AninternalpulluptoVccwillkeepDISABLEhighifpinleftopen.

PWM INPUT-IstheTTLcompatibledigitalinputforcontrollingthePWMpulsewidthofthebridge.Adutycycle

greaterthan50%willproducegreaterthan50%dutycyclepulsesoutoftheAout.Adutycyclelessthan50%

willproducegreaterthan50%dutycyclefromtheBout.Foranaloginputs,theintegrationcapacitorforthe

internalclockmustbeconnectedbetweenthispinandanalogground.Theinternalswitchingfrequencyispro-

grammableupto125kHzbyselectionoftheintegrationcapacitor.Theformulais:

BYPASSING

Adequatebypassingofthepowersuppliesisrequiredforproperoperation.Failuretodosocancauseerraticand

lowefficiencyoperationaswellasexcessiveringingattheoutputs.TheVssupplyshouldbebypassedwithat

leasta1µFceramiccapacitorinparallelwithanotherlowESRcapacitorofatleast10µFperampofoutputcurrent.

Capacitortypesratedforswitchingapplicationsaretheonlytypesthatshouldbeconsidered.The1µFceramic

capacitormustbephysicallyconnecteddirectlytotheVsandPOWERGNDpins.Evenoneinchofleadlengthwill

causeexcessiveringingattheoutputs.Thisisduetotheveryfastswitchingtimesandtheinductanceofthelead

connection.ThebypassingrequirementsoftheVccsupplyarelessstringent,butstillnecessary.A.1µFto.47µF

ceramiccapacitorconnecteddirectlytotheVccandANALOGGNDpinswillsuffice.

PCB LAYOUT

ThedesignerneedstoappreciatethattheSA60combinesinonecircuitbothhighspeedhighpowerswitchingand

lowlevelanalogsignals.Certainlayoutrulesofthumbmustbeconsideredwhenacircuitboardlayoutisdesigned

usingtheSA60:

1. Bypassingofthepowersuppliesiscritical.Capacitorsmustbeconnecteddirectlytothepowersupplypinswith

veryshortleadlengths(wellunder1inch).Ceramicchipcapacitorsarebest.

2. ConnectANALOGGNDtoPOWERGNDwithaconductorhavingnointermediateconnections.ConnectallVs

powersupply,filterandloadrelatedgroundconnectionstoPOWERGNDkeepingtheseconductorsseparate

– 50

C

1.44 x10

Fsw

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