T

J +

T

A )

P

θJA

RθJA +

T

P

P

(5 * 2.5) V x 1 A + 2.5 W

RθJAmax + (125 * 55)°C 2.5 W + 28°C W

15

20

25

30

35

40

0.1

1

10

100

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)

(6)

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

10

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