Datasheet

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SLVS293D − NOVEMBER 2000 − REVISED MAY 2002
15
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
THERMAL INFORMATION
TO−220 power dissipation
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 Data section at the end of the data sheet. A
heatsink can be used with the TO−220 package to effectively lower the junction-to-ambient thermal resistance.
To illustrate, the TPS75525 in a TO−220 package was chosen. For this example, the average input voltage is
3.3 V, the output voltage is 2.5 V, the average output current is 3 A, 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:
P
D
max +
(
3.3–2.5
)
Vx3A + 2.4 W
(5)
Substituting T
J
max for T
J
into equation 4 gives equation 6:
R
θJA
max + (125 – 55)°Cń2.4 W + 29°CńW
(6)
From Figure 22, R
θJA
vs Heatsink Thermal Resistance, a heatsink with R
θSA
= 22°C/W is required to dissipate
2.4 W. The model operating environment used in the computer model to construct Figure 22 consisted of a
standard JEDEC High-K board (2S2P) with a 1 oz. internal copper plane and ground plane. Since the package
pins were soldered to the board, 450 mm
2
of the board was modeled as a heatsink. Figure 23 shows the side
view of the operating environment used in the computer model.
Figure 22
5
15
25
35
45
55
65
0510152025
R
θSA
− Heatsink Thermal Resistance − °C/W
THERMAL RESISTANCE
vs
HEATSINK THERMAL RESISTANCE
− Thermal Resistance −
θJA
R C/W
°
No Heatsink
Natural Convection
Air Flow = 150 LFM
Air Flow = 250 LFM
Air Flow = 500 LFM