Datasheet
SLVS293D − NOVEMBER 2000 − REVISED MAY 2002
17
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
THERMAL INFORMATION
TO−263 power dissipation
The TO−263 package provides an effective means of managing power dissipation in surface mount
applications. The TO−263 package dimensions are provided in the Mechanical Data section at the end of the
data sheet. The addition of a copper plane directly underneath the TO−263 package enhances the thermal
performance of the package.
To illustrate, the TPS75525 in a TO−263 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
(7)
Substituting T
J
max for T
J
into equation 4 gives equation 8:
R
θJA
max + (125 – 55)°Cń2.4 W + 29°CńW
(8)
From Figure 25, R
θJA
vs Copper Heatsink Area, the ground plane needs to be 2 cm
2
for the part to dissipate
2.4 W. The model operating environment used in the computer model to construct Figure 25 consisted of a
standard JEDEC High-K board (2S2P) with a 1 oz. internal copper plane and ground plane. The package is
soldered to a 2 oz. copper pad. The pad is tied through thermal vias to the 1 oz. ground plane. Figure 26 shows
the side view of the operating environment used in the computer model.
Figure 25
15
20
25
30
35
40
0 0.01 0.1 1 10 100
THERMAL RESISTANCE
vs
COPPER HEATSINK AREA
Copper Heatsink Area − cm
2
− Thermal Resistance −
θJA
R C/W
°
No Air Flow
150 LFM
250 LFM