MSK105(2000) Просмотр технического описания (PDF) - M.S. Kennedy

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Компоненты Описание

производитель

MSK105
(Rev.:2000)

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

amplifiers. For this thermal analysis, each die will be

considered individually. In our example the amplifier ap-

plication requires each output to drive a 10 volt peak

sine wave across a 20 ohm load for 0.5 amp of output

current. For a worst case analysis we will treat the 0.5

amp peak output current as a D.C. output current. The

power supplies are ±20VDC.

1.) Find Driver Power Dissipation

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

[(VCC-VO) x IOUT X 2]

= (75mA) x (40V) + (10V) x (0.5A) + (10V) x (0.5A)

= 3W + 10W

= 13W

2.) For conservative design, set TJ=+150°C.

3.) For this example, worst case TA=+25°C

4.) RθJC = 4.0°C/W typically

5.) RθCS = 0.15°C/W for most thermal greases

6.) Rearrange governing equation to solve for RθSA

RθSA = ((TJ - TA)/PD) - (RθJC) - (RθCS)

= ((150°C - 25°C) / 13W) - (4°C/W) - (.15°C/W)

≅ 5.5°C/W

The heat sink in this example must have a thermal

resistance of no more than 5.5°C/W to maintain a junc-

tion temperature of no more than +150°C.

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. C 8/00

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