MSK105B 查看數據表（PDF） - M.S. Kennedy

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MSK105B

HIGH POWER QUAD OPERATIONAL AMPLIFIER

M.S. Kennedy 

APPLICATION NOTES CONTINUED

HEAT SINKING

To determine if a heat sink is necessary for your appli-

cation and if so, what type, refer to the thermal model

and governing equation below.

Thermal

Model:

Example:

Inside the MSK 105 package are two monolithic dual amplifi-

ers that do not exhibit thermal crossover (die to die) at 45°

spreading angle. Therefore, our example will focus on only one

of the two die. Further, consideration must be taken to calcu-

late power dissipation on each amplifier of the die to determine

worst case power dissipation. Only the worst case amplifier

will be used in this example. In our example, the amplifer is

required to drive 10 volts across a 20 ohm load. This calcu-

lates to 0.5 amps of output current. The power supplies are

±20 Vdc.

1.) To Find Power Dissipation

PD = [(quiescent current) x (+VCC - (-VCC))] + (VCC - VO) x IOUT

PD = 37.5 mA* x 40V + 10V x 0.5A

PD = 1.5W + 5W

PD = 6.5W

*quiescent current for one amplifier is 1/4 of entire quiescent current.

Tj shall be 150°C

Ta shall be 25°C

Rθjc = 8.0°C/W

Rθcs = 0.15°C/W (most thermal greases)

2.) Rearrange the governing equation to solve for RθSA

(heat sink to air)

Rθsa = ((Tj - TA)/PD) - Rθjc - Rθcs

= ((150°C - 25°C)/6.5W) - 8.0°C/W - 0.15°C/W

= 11.08°C/W

Therefore, to maintain a junction temperature of no more than

150°C for that amplifier, the heat sink must have a thermal

resistance of no more than 11.1°C/W.

Thermal Path:

Governing Equation:

TJ=PD x (RθJC + RθCS + RθSA) + TA

Where

TJ = Junction Temperature

PD = Total Power Dissipation

RθJC = Junction to Case Thermal Resistance

RθCS = Case to Heat Sink Thermal Resistance

RθSA = Heat Sink to Ambient Thermal Resistance

TC = Case Temperature

TA = Ambient Temperature

TS = Sink Temperature

4

Rev. D 10/01

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