PA93

PA93U

5

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

®

SAFE OPERATING AREA (SOA)

TheMOSFEToutputstageofthispoweroperationalam-

plifierhastwodistinctlimitations:

1. ThecurrenthandlingcapabilityoftheMOSFETgeom-

etryandthewirebonds.

2. ThejunctiontemperatureoftheoutputMOSFETs.

NOTE: The output stage is protected against transient

flyback.However,forprotectionagainstsustained,high

energyflyback,externalfast-recoverydiodesshouldbe

used.

SAFE OPERATING CURVES

Thesafeoperatingareacurvesdefinethemaximumad-

ditionalinternalpowerdissipationtheamplifiercantoler-

ate when it produces the necessary output to drive an

externalload.

INPUT PROTECTION

AlthoughthePA93canwithstanddifferentialvoltagesup

to±20V,additionalexternalprotectionisrecommended.

Low leakage, low capacitance JFETs connected as di-

odesarerecommended(e.g.2N4416,Q1-Q4inFigure2).Thedifferen-

tialinputvoltagewillbeclampedto±1.4V.Thisissufficientoverdriveto

producemaximumpowerbandwidth.

POWER SUPPLY PROTECTION

Unidirectionalzenerdiodetransientsuppressorsarerecommendedas

protectiononthesupplypins.SeeFigure2.Thezenersclamptransients

tovoltageswithinthepowersupplyratingandalsoclamppowersupply

reversals to ground. Whether the zeners are used or not, the system

powersupplyshouldbeevaluatedfortransientperformanceincluding

power-onovershootandpower-offpolarityreversalsaswellaslineregu-

lation.

Conditionswhichcancauseopencircuitsorpolarityreversalsoneither

powersupplyrailshouldbeavoidedorprotectedagainst.Reversalsoropensonthenegativesupplyrailisknown

toinduceinputstagefailure.Unidirectionaltranszorbspreventthis,anditisdesirablethattheybebothelectrically

andphysicallyasclosetotheamplifieraspossible.

STABILITY

ThePA93isexternallycompensatedandperformancecanbetailoredtotheapplication.Usethegraphsofsmall

signalresponseandpowerresponseasaguide.ThecompensationcapacitorC

voltage.AnNPOcapacitorisrecommended.ThecompensationnetworkC

plifierpins4and5toavoidspuriousoscillation.

QUIESCENT CURRENT REDUCTION

Whenpin3(I

butalsoraisesdistortionsincetheoutputstageisthenclassCbiased.Theoutputstagebiascurrentisnominally

setat1mA.Pin3maybeleftopenifnotused.

SUPPLY TO OUTPUT DIFFERENTIAL, V

10

20

30 40

100

200 300

500

.1

.08

.06

.6

.4

.3

.2

.8

3

2

1

4

6

8

20

10

DC,T

C

= 125C

100mS

60 80

200mS

DC, T

DC,T

C

= 85C

SOA

–IN

+IN

Z1

Z2

11, 12

7, 8

1

2

6

PA93

Q1

Q2

Q3

Q4

FIGURE 2.

OVERVOLTAGE

PROTECTION