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.
Thermal Model:
RΘSA = ((TJ - TA)/PD) - (RΘJC) - (RΘCS)
= ((125°C - 80°C) / 0.36W) - 55°C/W - 0.15°C/W
= 125 - 55.15
= 69.9°C/W
This heat sink in this example must have a thermal resistance
of no more than 69.9°C/W to maintain a junction temperature
of no more than +125°C.
Typical Applications:
Governing Equation:
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
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
TOTAL DOSE RADIATION TEST
PERFORMANCE
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 = 55° C/W from MSK 0002RH Data Sheet
5.) RΘCS = 0.15° C/W for most thermal greases
6.) Rearrange governing equation to solve for RΘSA
Radiation performance curves for TID testing have been
generated for all radiation testing performed by MS
Kennedy. These curves show performance trends
throughout the TID test process and can be located in
the MSK 0002RH radiation test report. The complete
radiation test report is available in the RAD HARD PROD-
UCTS section on the MSK website.
http://www.mskennedy.com/store.asp?pid=9951&catid=19680
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8548-2 Rev. D 10/12