Datasheet
www.ti.com
1
10
01020
− Power Dissipation Limit − W
P
D
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
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)
TPS75901, TPS75915
TPS75918, TPS75925, TPS75933
SLVS318E – DECEMBER 2000 – REVISED MARCH 2004
THERMAL INFORMATION (continued)
Figure 24. Power Dissipation vs Heatsink Thermal Resistance
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 TPS75925 in a TO-263 package was chosen. For this example, the average input voltage is
3.3V, 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:
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
2.4W. 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.
17