0

10

20

30

40

50

60

0

5

10

15

20

25

30

35

40

BOARD AREA (cm

2

)

0LFM (0m/s) air

225LFM (1.14m/s) air

500LFM (2.54m/s) air

Evaluation Board Area

LMZ14202H

SNVS691H – JANUARY 2011 – REVISED OCTOBER 2015

www.ti.com

Power Dissipation and Board Thermal Requirements (continued)

To achieve this thermal resistance the PCB is required to dissipate the heat effectively. The area of the PCB will

have a direct effect on the overall junction-to-ambient thermal resistance. In order to estimate the necessary

copper area we can refer to the following Figure 54. Figure 54 is taken from the Typical Characteristics section

and shows how the RθJA varies with the PCB area.

Figure 54. Package Thermal Resistance RθJA 4-Layer Printed-Circuit-Board With 1-oz Copper

For RθJA-MAX< 22.2°C/W and only natural convection (that is, no air flow), the PCB area will have to be at least 30

cm2. This corresponds to a square board with approximately 5.5cm × 5.5cm (2.17in × 2.17in) copper area, 4

layers, and 1-oz copper thickness. Higher copper thickness will further improve the overall thermal performance.

Note that thermal vias should be placed under the IC package to easily transfer heat from the top layer of the

PCB to the inner layers and the bottom layer.

For more guidelines and insight on PCB copper area, thermal vias placement, and general thermal design

practices refer to Application Note AN-2020 (SNVA419).

24

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