each interface is equal to the total power dissipated in the device times the thermal resistance (PD 鈥?/div>
胃).
+ PD 鈥?/div>
胃
JA
Where,
胃
JA
=
胃
JC
+
胃
CH
+
胃
HA
T
A
(擄C) = Temperature of Ambient Air
T
J
(擄C) = Temperature of the Semiconductor Junction
PD (Watts) = Power Dissipated in Semiconductor
胃
JC
(擄C/Watt) = Thermal Resistance (Junction to Case)
胃
CH
(擄C/Watt) = Thermal Resistance (Case to Heat Sink)
胃
HA
(擄C/Watt) = Thermal Resistance (Heat Sink to Air)
胃
JA
(擄C/Watt) = Thermal Resistance (Junction to Air)
The following example shows typical values for a TO-3 package mounted in two different ways 鈥?one for high power
applications, the other for low power applications. The value for
胃
JC
of 0.8擄C/W is for the OPA512 operating under
AC signal conditions. For DC signal conditions,
胃
JC
is about 1.4擄C/W.
Power Dissipated
Junction
PD
T
J
胃
JC
UNITS
Watts
擄C
擄C/Watt
擄C
擄C/Watt
擄C
擄C/Watt
擄C
HIGH POWER
APPLICATION
100W
145擄C
0.8
65擄C
0.1
55擄C
0.3
25擄C
10W
37擄C
*
0.8
29擄C
0.1
28擄C
0.3
25擄C
LOW POWER
APPLICATION
10W
158擄C
*
0.8
150擄C
0.5
145擄C
12
25擄C
1W
39擄C
0.8
38擄C
0.5
37擄C
12
25擄C
Case
Mounting
Resistance
Heat Sink
T
C
胃
CH
T
H
胃
HA
Ambient Air
T
A
*
Note, the difference in junction temperature that thermal resistance
can make even when operating at the same power level.
Calculations begin at the bottom of the chart and assume 25擄C ambient temperature in these examples. Each component of
thermal resistance produces a temperature rise equal to the product of power dissipated and thermal resistance. The
temperature of the junction is equal to the product of power dissipated and the total thermal resistance (PD 鈥?/div>
胃
JA
).
Thermal resistances can vary significantly with particular models and mounting. While
胃
values can be obtained from
specifications, calculated temperatures should be confirmed by measurements made at the bottom of the case.
The information provided herein is believed to be reliable; however, BURR-BROWN assumes no responsibility for inaccuracies or omissions. BURR-BROWN assumes
no responsibility for the use of this information, and all use of such information shall be entirely at the user鈥檚 own risk. Prices and specifications are subject to change
without notice. No patent rights or licenses to any of the circuits described herein are implied or granted to any third party. BURR-BROWN does not authorize or warrant
any BURR-BROWN product for use in life support devices and/or systems.
漏
1992 Burr-Brown Corporation
AB-038
Printed in U.S.A. August, 1992
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