To determine if a heat sink is necessary for your application
and if so, what type, refer to the thermal model and governing
RΘSA = ((TJ - TA)/PD) - (RΘJC) - (RΘCS)
= ((125°C - 80°C) / 0.36W) - 40°C/W - 0.15°C/W
= 125 - 40.15
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
PD=Total Power Dissipation
RΘJC=Junction to Case Thermal Resistance
RΘCS=Heat Sink to Ambient Thermal Resistance
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.
Vo= ±6Vp Sine Wave, Freq. = 1KHz
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)
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
Rev. - 10/00