Datasheet

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TO-220 Power Dissipation
P
D
max +
(
3.3 * 2.5
)
V 3A + 2.4W
(7)
R
QJA
max +
(
125 * 55
)
°C
2.4W
+ 29°CńW
(8)
5
15
25
35
45
55
65
0510152025
R
θ
SA
− Heatsink Thermal Resistance − °C/W
− Thermal Resistance −
θJA
R C/W
°
No Heatsink
Natural Convection
Air Flow = 150 LFM
Air Flow = 250 LFM
Air Flow = 500 LFM
TPS75801 , , TPS758A01
TPS75815 , TPS75818
TPS75825 , TPS75833
SLVS330F – JUNE 2001 – REVISED APRIL 2007
THERMAL INFORMATION (continued)
The TO-220 package provides an effective means of managing power dissipation in through-hole applications.
The TO-220 package dimensions are provided in the mechanical drawings at the end of this data sheet. A
heatsink can be used with the TO-220 package to effectively lower the junction-to-ambient thermal resistance.
To illustrate, the TPS75825 in a TO-220 package was chosen. For this example, the average input voltage is
3.3V, the average output voltage is 2.5V, the average output current is 3A, the ambient temperature +55 ° C, the
air flow is 150 LFM, and the operating environment is the same as documented below. Neglecting the quiescent
current, the maximum average power is:
Substituting T
J
max for T
J
in Equation 6 results in Equation 8 :
From Figure 23 , R
Θ JA
vs Heatsink Thermal Resistance, a heatsink with R
Θ SA
= 22 ° C/W is required to dissipate
2.4W. The model operating environment used in the computer model to construct Figure 23 consisted of a
standard JEDEC High-K board (2S2P) with a 1-ounce internal copper plane and ground plane. Since the
package pins were soldered to the board, 450mm
2
of the board was modeled as a heatsink. Figure 24 shows
the side view of the operating environment used in the computer model.
Figure 23. Thermal Resistance vs Heatsink Thermal Resistance
14
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