RT8015
The maximum power dissipation depends on operating
ambient temperature for fixed TJ(MAX) and thermal
resistance qJA. 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 qJA 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 qJA can be
decreased by adding a copper under the exposed pad of
SOP-8 (Exposed Pad) package.
(a) CopperArea = (2.3 x 2.3) mm2, qJA = 75°C/W
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), qJA is 75°C/W. Adding
copper area of pad under theSOP-8 (Exposed Pad)(Figure
4.b) reduces the qJA to 64°C/W. Even further, increasing
the copper area of pad to 70mm2 (Figure 4.e) reduces the
qJA to 49°C/W.
(b) CopperArea = 10mm2, qJA = 64°C/W
2.4
(c) CopperArea = 30mm2, qJA = 54°C/W
Copper Area
70mm2
50mm2
2
30mm2
10mm2
1.6
Min. layout
1.2
0.8
0.4
0
(d) CopperArea = 50mm2, qJA = 51°C/W
0
20
40
60
80
100
120
140
(°C)
Ambient Temperature (°C)
Figure 3.Derating Curve for Package
(e) CopperArea = 70mm2, qJA = 49°C/W
Figure 4. Thermal Resistance vs. CopperArea Layout
ThermalDesign
DS8015-03 March 2011
www.richtek.com
13
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
