RT8284N
Thermal Considerations
(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
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 :
θJA to 49°C/W.
The maximum power dissipation depends on operating
ambient temperature for fixed TJ(MAX) and thermal
resistance θJA. The of de-rating curves in Figure 7 allow
the designer to see the effect of rising ambient temperature
on the maximum power dissipation allowed.
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.
2.2
Four-Layer PCB
2.0
1.8
1.6
1.4
Copper Area
70mm2
50mm2
For recommended operating conditions specification, 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
30mm2
10mm2
1.2
Min.Layout
1.0
0.8
0.6
0.4
0.2
0.0
SOP-8
θ
JA 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 :
0
25
50
75
100
125
Ambient Temperature (°C)
Figure 7. Derating Curve of Maximum PowerDissipation
(a) Copper Area = (2.3 x 2.3) mm2,θJA = 75°C/W
(b) Copper Area = 10mm2,θJA = 64°C/W
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
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12
DS8284N-03 May 2012
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
