Datasheet
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1
10
01020
– Power Dissipation Limit – W
P
D
POWER DISSIPATION LIMIT
vs
HEATSINK THERMAL RESISTANCE
R
θ
SA
– Heatsink Thermal Resistance – °C/W
No Heatsink
T
A
= 55°C
Natural Convection
Air Flow = 150 LFM
Air Flow = 250 LFM
Air Flow = 500 LFM
TO-263 Power Dissipation
P
D
max
(
3.3 – 2.5
)
V x 3 A 2.4 W
(7)
R
θJA
max (125 – 55)°C2.4 W 29°CW
(8)
TPS75601, TPS75615
TPS75618, TPS75625
TPS75633
SLVS329C – JUNE 2001 – REVISED MARCH 2004
THERMAL INFORMATION (continued)
Figure 24.
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 TPS75625 in a TO-263 package was chosen. For this example, the average input voltage is 3.3
V, the average 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:
Substituting T
J
max for T
J
into Equation 4 gives Equation 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.
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