MSK0002 datasheet(3/5 Pages) MSK

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APPLICATION NOTES

HEAT SINKING

To determine if a heat sink is necessary for your application

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

equation below.

RΘSA = ((TJ - TA)/PD) - (RΘJC) - (RΘCS)

= ((125°C - 80°C) / 0.36W) - 40°C/W - 0.15°C/W

= 125 - 40.15

= 84.9°C/W

This heat sink in this example must have a thermal resistance

of no more than 84.9°C/W to maintain a junction temperature

of no more than +125°C.

TJ=PD X (RΘJC +RΘCS +RΘSA) +TA

Where

TJ=Junction Temperature

PD=Total Power Dissipation

RΘJC=Junction to Case Thermal Resistance

RΘCS=Heat Sink to Ambient Thermal Resistance

TC=Case Temperature

TA=Ambient Temperature

TS=Sink Temperature

Thermal Model:

Rev. - 10/00

Governing Equation:

Example:

This example demonstrates a worst case analysis for the buffer

output stage. This occurs when the output voltage is 1/2 the

power supply voltage. Under this condition, maximum power

transfer occurs and the output is under maximum stress.

Conditions:

VCC= ±12VDC

Vo= ±6Vp Sine Wave, Freq. = 1KHz

RL= 100Ω

For a worst case analysis we will treat the ±6Vp sine wave as

an 6 VDC output voltage.

1.) Find Driver Power Dissipation

PD= (Vcc-Vo) (Vo/RL)

= (12V-6V) (6V/100Ω)

= 360mW

2.) For conservative design, set TJ=+125°C Max.

3.) For this example, worst case TA=+80°C

4.) RΘJC = 40° C/W from MSK 0002H Data Sheet

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

6.) Rearrange governing equation to solve for RΘSA

Typical Applications:

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