HEAT SINKING

To select the correct heat sink for your application, re-

fertothethermalmodelandgoverningequationbelow.

Thermal Model:

APPLICATION NOTES

CURRENT LIMIT

The MSK0021 has an on-board current limit scheme

designed to limit the output drivers anytime output current

exceeds a predetermined limit.The following formula may

be used to determine the value of the current limit resis-

tancenecessarytoestablishthedesiredcurrentlimit.

Current Limit Connection

3

___

See "Application Circuits" in this data sheet for ad-

ditionalinformationoncurrentlimitconnections.

POWER SUPPLY BYPASSING

Both the negative and the positive power supplies must be

effectively decoupled with a high and low frequency bypass

circuittoavoidpowersupplyinducedoscillation.Aneffective

decouplingschemeconsistsofa0.1microfaradceramicca-

pacitorinparallelwitha4.7microfaradtantalumcapacitorfrom

eachpowersupplypintoground.Itisalsoagoodpracticewith

high power op-amps, such as the MSK0021, to place a 30-50

microfarad capacitor with a low effective series resistance, in

parallelwiththeothertwopowersupplydecouplingcapacitors.

This capacitor will eliminate any peak output voltage clipping

whichmayoccurduetopoorpowersupplyloadregulation.

All power supply decoupling capacitors should be placed as

closetothepackagepowersupplypinsaspossible.

SAFE OPERATING AREA

The safe operating area curve is a graphical representation

ofthepowerhandlingcapabilityoftheamplifierundervarious

conditions.Thewirebondcurrentcarryingcapability,transistor

junction temperature and secondary breakdown limitations

areallincorporatedintothesafeoperatingareacurves.All

applicationsshouldbecheckedagainsttheS.O.A.curvesto

ensurehighM.T.B.F.

Governing Equation:

Where

= Junction Temperature

= Total Power Dissipation

= Junction to Case Thermal Resistance

= Heat Sink to Ambient Thermal Resistance

= Case Temperature

= Ambient Temperature

= Sink Temperature

Inourexampletheamplifierapplicationrequirestheoutputtodrivea

10voltpeaksinewaveacrossa10ohmloadfor1ampofoutputcurrent.

For a worst case analysis we will treat the 1 amp peak output current

asaD.C.outputcurrent.Thepowersuppliesare±15VDC.

1.) FindPowerDissipation

=(3.5mA)X(30V)+(5V)X(1A)

=0.1W+5W

=5.1W

=(125°C-25°C)/5.1W-(2.0°C/W)-(0.15°C/W)

=17.5°C/W

The heat sink in this example must have a thermal resistance of no

morethan17.5°C/Wtomaintainajunctiontemperatureoflessthan

+125°C.

8548-83Rev.E9/15