HEAT SINKING

To select the correct heat sink for your application, refer to the

thermal model and governing equation below.

Thermal Model:

APPLICATION NOTES

CURRENT LIMIT

The MSK 0041 has an on-board current limit scheme de-

signed 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 resistance

necessary to establish the desired current limit.

Current Limit Connection

3

Rev. - 4/02

___

See "Application Circuits" in this data sheet for additional

information on current limit connections.

POWER SUPPLY BYPASSING

Both the negative and the positive power supplies must

be effectively decoupled with a high and low frequency by-

pass circuit to avoid power supply induced oscillation. An

effective decoupling scheme consists of a 0.1 microfarad

ceramic capacitor in parallel with a 4.7 microfarad tantalum

capacitor from each power supply pin to ground.This ca-

pacitor will eliminate any peak output voltage clipping which

may occur due to poor power supply load regulation. All

power supply decoupling capacitors should be placed as

close to the package power supply pins as possible.

SAFE OPERATING AREA

The safe operating area curve is a graphical representation

of the power handling capability of the amplifier under vari-

ous conditions. The wire bond current carrying capability,

transistor junction temperature and secondary breakdown

limitations are all incorporated into the safe operating area

curves. All applications should be checked against the curves

to ensure high M.T.B.F.

Governing Equation:

Where

= Junction Temperature

= Total Power Dissipation

= Junction to Case Thermal Resistance

= Case to Heat Sink Thermal Resistance

= Heat Sink to Ambient Thermal Resistance

= Case Temperature

= Ambient Temperature

= Sink Temperature

In our example the amplifier application requires the output to drive

a 10 volt peak sine wave across a 100 ohm load for 0.1 amp of

output current. For a worst case analysis we will treat the 0.1 amp

peak output current as a D.C. output current. The power supplies

are ±15 VDC.

1.) Find Power Dissipation

=(3.5 mA) X (30V) + (5V) X (0.1A)

=0.1W + 0.5W

=0.6W

= (150°C - 25°C) / 0.6W - (85°C/W) - (0.15°C/W)

= 123°C/W

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

more than 123°C/W to maintain a junction temperature of less than

+150°C. This calculation assumes a case to sink thermal resistance

of 0.15°C/W.