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

PA91

PA91U



GENERAL

PleasereadApplicationNote1"GeneralOperatingConsiderations"whichcoversstability,supplies,heatsinking,

mounting,currentlimit,SOAinterpretation,andspecificationinterpretation.Visitwww.cirrus.comfordesigntools

thathelpautomatetaskssuchascalculationsforstability,internalpowerdissipation,currentlimit;heatsinkselec-

tion;Apex’scompleteApplicationNoteslibrary;TechnicalSeminarWorkbook;andEvaluationKits.

CURRENTLIMIT

Forproperoperation,thecurrentlimitresistor(R

gram.Foroptimumreliabilitytheresistorvalueshouldbesetashighaspossible.Thevalueiscalculatedasfollows;

withthemaximumpracticalvalueof32ohms.

.65

R

I

LIM

SAFEOPERATINGAREA(SOA)

The MOSFET output stage of this power operational

amplifierhastwodistinctlimitations:

1. ThecurrenthandlingcapabilityoftheMOSFETge-

ometryandthewirebonds.

2. ThejunctiontemperatureoftheoutputMOSFETs.

NOTE:Theoutputstageisprotectedagainsttransient

flyback.However,forprotectionagainstsustained,high

energyflyback,externalfast-recoverydiodesshouldbe

used.

SAFEOPERATINGCURVES

The safe operating area curves define the maximum

additional internal power dissipation the amplifier can

toleratewhenitproducesthenecessaryoutputtodrive

anexternalload.

TYPICALAPPLICATION

LOWPOWER,PIEZOELECTRICPOSITIONING

Piezopositioningmaybeappliedtothefocusingofseg-

mented mirror systems. The composite mirror may be

composedofhundredsofelements,eachrequiringfocus-

ingundercomputercontrol.Insuchcomplexsystemsthe

PA91 reduces the costs of power supplies and cooling

withitsadvantagesoflowcostandlowquiescentpower

consumptionwhileincreasingcircuitdensitywiththeSIP

package.

PHASECOMPENSATION

GAIN

C

R

≥1

68pF

100Ω

≥5

10pF

100Ω

≥10

4.7pF

0Ω

≥30

NONE

0Ω

*C