RT7248 datasheet(13/15 Pages) RICHTEK

13 / 15 page

RT7248

DS7248-01

September 2012

www.richtek.com

is a registered trademark of Richtek Technology Corporation.

increasing the copper area of pad to 70mm2 (Figure 7.e)

reduces the

θJA to 49°C/W.

The maximum power dissipation depends on operating

ambient temperature for fixed TJ(MAX) and thermal

resistance

θJA. The Figure 8 of derating curves allows the

designer to see the effect of rising ambient temperature

on the maximum power dissipation allowed.

Figure 8. Derating Curve of Maximum Power Dissipation

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

100

125

Ambient Temperature (°C)

Copper Area

70mm

50mm

30mm

10mm

Min.Layout

Four-Layer PCB

(a) Copper Area = (2.3 x 2.3) mm2,

θJA = 75°C/W

(b) Copper Area = 10mm2,

θJA = 64°C/W

2 ,

θJA = 54°C/W

(d) Copper Area = 50mm2 ,

θJA = 51°C/W

(e) Copper Area = 70mm2 ,

θJA = 49°C/W

Figure 7. Themal Resistance vs. Copper Area Layout

Design

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