The maximum power dissipation depends on operating
ambient temperature for fixed TJ(MAX) and thermal
resistance θJA. For RT8015 package, the Figure 3 of de-
rating curves allows the designer to see the effect of rising
ambient temperature on the maximum power allowed.
The thermal resistance θJA of SOP-8 (Exposed Pad) is
determined by the package design and the PCB design.
However, the package design had been designed. If
possible, it’ s useful to increase thermal performance by
the PCB design. The thermal resistance θJA can be
decreased by adding a copper under the exposed pad of
SOP-8 (Exposed Pad) package.
As shown in Figure 4, the amount of copper area to which
the SOP-8 (Exposed Pad) is mounted affects thermal
performance. When mounted to the standard SOP-8
(Exposed Pad) pad (Figure 4.a), θJA is 75°C/W. Adding
copper area of pad under the SOP-8 (Exposed Pad) (Figure
4.b) reduces the θJA to 64°C/W. Even further, increasing
the copper area of pad to 70mm2 (Figure 4.e) reduces the
θJA to 49°C/W.
2.4
Copper Area
70mm2
2
50mm2
30mm2
1.6
10mm2
Min. layout
1.2
0.8
0.4
0
0
20
40 60
80 100 120 140
Ambient Temperature (°CC)
Figure 3. Derating Curve for Package
RT8015
(a) Copper Area = (2.3 x 2.3) mm2, θJA = 75°C/W
(b) Copper Area = 10mm2, θJA = 64°C/W
(c) Copper Area = 30mm2, θJA = 54°C/W
(d) Copper Area = 50mm2, θJA = 51°C/W
(e) Copper Area = 70mm2, θJA = 49°C/W
Figure 4. Thermal Resistance vs. Copper Area Layout
Thermal Design
DS8015-03 March 2011
www.richtek.com
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