PA98 • PA98A

PA98U

5

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

GENERAL

PleasereadApplicationNote1"GeneralOperatingConsiderations"whichcoversstability,supplies,heatsinking,

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

thathelpautomatetaskssuchascalculationsforstability,internalpowerdissipation,currentlimit;heatsinkselec-

tion;ApexPrecisionPower’scompleteApplicationNoteslibrary;TechnicalSeminarWorkbook;andEvaluationKits.

CURRENT LIMIT

Forproperoperation,thecurrentlimitresistor(R

gram.Theminimumvalueis1.4ohm,howeverforoptimumreliabilitytheresistorvalueshouldbesetashighas

possible.Thevalueiscalculatedasfollows;withthemaximumpracticalvalueof30ohms.

.7

R

I

SAFE OPERATING AREA (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.

SAFE OPERATING CURVES

The safe operating area curves define the maximum

additional internal power dissipation the amplifier can

toleratewhenitproducesthenecessaryoutputtodrive

anexternalload.Thisisnotthesameastheabsolute

maximuminternalpowerdissipationlistedelsewherein

thespecificationsincethequiescentpowerdissipation

issignificantcomparedtothetotal.

SOA

SUPPLY TO OUTPUT DIFFERENTIAL, V

25

50

75 100 125

250

500

500

300

200

100

50

30

20

10

PULSE CURVES @ 10% DUTY CYCLE MAX.

100mS

200mS

DC,

T

C

= 25°C

DC,

T

C

= 125°C

DC,

T

C

= 85°C

TYPICAL APPLICATION

DYNAMIC FOCUSING

Dynamicfocusingistheactivecorrectionoffocusingvoltage

asabeamtraversesthefaceofaCRT.Thisisnecessaryin

highresolutionflatfacemonitorssincethedistancebetween

cathodeandscreenvariesasthebeammovesfromthecenter

ofthescreentotheedges.PA98lendsitselfwelltothisfunc-

tion since it can be connected as a summing amplifier with

inputsfromthenominalfocuspotentialandthedynamiccor-

rection.Thenominalmightbederivedfromapotentiometer,or

perhapsautomaticfocusingcircuitrymightbeusedtogeneratethispotential.Thedynamiccorrectionisgenerated

fromthesweepvoltagesbycalculatingthedistanceofthebeamfromthecenterofthedisplay.

PHASE COMPENSATION

Gain

C

C

R

C

1

68pF

100Ω

20

10pF

330Ω

100

3.3pF

0Ω

C

2

IN1

R

F

R

CL

R

+225V

225V

PA98

IN2

R

DC

FOCUS

X SWEEP

SAMPLE

Y SWEEP

SAMPLE

TO

FOCUS

GRID