RT8284 データシートの表示（PDF） - Richtek Technology
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RT8284 Datasheet PDF : 15 Pages
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RT8284
Thermal Considerations
For continuous operation, do not exceed absolute
maximum operation junction temperature 125°C. The
maximum power dissipation depends on the thermal
resistance of IC package, PCB layout, the rate of
surroundings airflow and temperature difference between
junctions to ambient. The maximum power dissipation can
be calculated by following formula :
PD(MAX) = (TJ(MAX) − TA) / θJA
Where TJ(MAX) is the maximum operation junction
temperature, TA is the ambient temperature and the θJA
is the junction to ambient thermal resistance.
For recommended operating conditions specification of
RT8284, the maximum junction temperature is 125°C. The
junction to ambient thermal resistance θJA is layout
dependent. For SOP-8 (Exposed Pad) package, the
thermal resistance θJA is 75°C/W on the standard JEDEC
51-7 four layers thermal test board. For SOP-8 package,
the thermal resistance θJA is 90°C/W on the standard
JEDEC 51-7 four layers thermal test board. The maximum
power dissipation at TA = 25°C can be calculated by
following formula :
PD(MAX) = (125°C − 25°C) / (75°C/W) = 1.33W
(min. copper area PCB layout with SOP-8 Exposed Pad)
PD(MAX) = (125°C − 25°C) / (49°C/W) = 2.04W
(70mm2 copper area PCB layout with SOP-8 Exposed
Pad)
PD(MAX) = (125°C − 25°C) / (90°C/W) = 1.11W
(min. copper area PCB layout with SOP-8)
The thermal resistance θJA of SOP-8 (Exposed Pad) is
determined by the package architecture design and the
PCB layout design. However, the package architecture
design had been designed. If possible, it's useful to increase
thermal performance by the PCB layout copper design.
The thermal resistance θJA can be decreased by adding
copper area under the exposed pad of SOP-8 (Exposed
Pad) package.
As shown in Figure 6, 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 6.a), θJA is 75°C/W. Adding
copper area of pad under the SOP-8 (Exposed Pad) (Figure
6.b) reduces the θJA to 64°C/W. Even further, increasing
the copper area of pad to 70mm2 (Figure 6.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. For RT8284 packages, the Figure 7 of de-
rating curves allows the designer to see the effect of rising
ambient temperature on the maximum power dissipation
allowed.
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0
Four-Layer PCB
Copper Area
70mm2
50mm2
30mm2
10mm2
Min.Layout
SOP-8
25
50
75
100
125
Ambient Temperature (°C)
Figure 7. Derating Curves for RT8284 Package
(a) Copper Area = (2.3 x 2.3) mm2, θJA = 75°C/W
(b) Copper Area = 10mm2, θJA = 64°C/W
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DS8284-01 March 2011
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