Datasheet

T
J
+ T
A
) P
D
max x R
θJA
R
θJA
+
T
J
–T
A
P
D
max
P
D
max +
(
5 * 2.5
)
V x 1 A + 2.5 W
R
θJA
max + (125 * 55)°Cń2.5 W + 28°CńW
15
20
25
30
35
40
0.1 1 10 100
Copper Heatsink Area − cm
2
− Thermal Resistance −
θJA
R C/W
°
No Air Flow
150 LFM
250 LFM
TPS726126
TPS72615, TPS72616
TPS72618, TPS72625
SLVS403H –MAY 2002–REVISED JUNE 2010 www.ti.com
Equation 2 simplifies into Equation 3:
(3)
Rearranging Equation 3 gives Equation 4:
(4)
Using Equation 3 and the computer model generated curves shown in Figure 20 and Figure 23, a designer can
quickly compute the required heatsink thermal resistance/board area for a given ambient temperature, power
dissipation, and operating environment.
DDPAK Power Dissipation
The DDPAK package provides an effective means of managing power dissipation in surface mount applications.
The DDPAK 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 DDPAK package enhances the thermal performance of the
package.
To illustrate, the TPS72625 in a DDPAK package was chosen. For this example, the average input voltage is 5
V, the output voltage is 2.5 V, the average output current is 1 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:
(5)
Substituting T
J
max for T
J
into Equation 4 gives Equation 6:
(6)
From Figure 20, DDPAK Thermal Resistance vs Copper Heatsink Area, the ground plane needs to be 1 cm
2
for
the part to dissipate 2.5 W. The operating environment used in the computer model to construct Figure 20
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 21 shows the side view of the operating environment used in the computer model.
Figure 20. DDPAK Thermal Resistance vs Copper Heatsink Area
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Product Folder Link(s): TPS726126 TPS72615 TPS72616 TPS72618 TPS72625