RT8282B RICHTEK [Richtek Technology Corporation], RT8282B Datasheet - Page 12

• Manufacturer Part Number: RT8282B
• Description: 2A, 23V, 1.2MHz Synchronous Step-Down Converter
• Manufacturer: RICHTEK [Richtek Technology Corporation]

RT8282B
Thermal Considerations
For continuous operation, do not exceed the 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 junction to ambient.
The maximum power dissipation can be calculated by
following formula :
P
Where
temperature ,
the junction to ambient thermal resistance.
For recommended operating conditions specification of
RT8282B, the maximum junction temperature is 125°C.
The junction to ambient thermal resistance
dependent. For PSOP-8 package, the thermal resistance
θ
thermal test board. The maximum power dissipation at
T
P
(min.copper area PCB layout)
P
(70mm
The thermal resistance
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
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), θ
Adding copper area of pad under the SOP-8 (Exposed
Pad) (Figure 6.b) reduces the θ
increasing the copper area of pad to 70mm
reduces the θ
The maximum power dissipation depends on operating
ambient temperature for fixed T
resistance θ
www.richtek.com
12
JA
A
D(MAX)
D(MAX)
D(MAX)
= 25°C
is 75°C/W on the standard JEDEC 51-7 four-layer
2
= (T
copper area PCB layout)
T
=
J(MAX)
=
can be calculated by following formula :
J(MAX)
(125°C
(125°C
JA
T
JA
. For RT8282B packages, the Figure 7 of
A
is the maximum operation junction
to 49°C/W.
is the ambient temperature and the
− T
A
− 25°C) / (75°C/W) = 1.333W
− 25°C) / (49°C/W) = 2.04W
) / θ
θ
JA
JA
of SOP-8 (Exposed Pad) is
JA
θ
to 64°C/W. Even further,
JA
can be decreased by
J(MAX)
and thermal
JA
2
θ
(Figure 6.e)
JA
is 75°C/W.
is layout
θ
JA
is
derating curves allows the designer to see the effect of
rising ambient temperature on the maximum power
dissipation allowed.
(a) Copper Area = (2.3 x 2.3) mm
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Figure 7. Derating Curves for RT8282B Package
(c) Copper Area = 30mm
(b) Copper Area = 10mm
0
25
Ambient Temperature (°C)
50
DS8282B-01 March 2011
2
2
, θ
, θ
75
JA
JA
2
, θ
= 64°C/W
= 54°C/W
Four-Layer PCB
JA
Copper Area
70mm
50mm
30mm
10mm
Min.Layout
= 75°C/W
100
2
2
2
2
125