RT9009 データシートの表示（PDF） - Richtek Technology
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RT9009 Datasheet PDF : 9 Pages
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RT9009
Applications Information
Thermal Considerations
For continuous operation, do not exceed absolute
maximum operation junction temperature. 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 :
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
RT9009, the maximum operating junction temperature is
125°C. The junction to ambient thermal resistance θJA is
layout dependent. As shown in Figure 2, RT9009
TO-263S-5 with 15mm x 15mm PCB copper area on the
standard JEDEC 51-7 four layers thermal test board
thermal resistance θJA is about 29°C/W. The maximum
power dissipation at TA = 25°C can be calculated by
following formula :
PD(MAX) = (125°C − 25°C) / (29°C/W) = 3.448W for
TO-263S-5 packages
Thermal Resistance vs. Copper Area
70
60
50
40
30
20
10
0
0
Single Layout PCB
Four Layout PCB
TO-263S-5
50 100 150 200 250 300 350 400
PCB Copper Area (mm2)
Figure 2. Thermal Resistance θJA vs. Copper Area of
TO-263S-5 Package
The maximum power dissipation depends on operating
ambient temperature for fixed TJ(MAX) and thermal
resistance θJA. For the RT9009, the Figure 3 of de-rating
curve allows the designer to see the effect of rising ambient
temperature on the maximum power dissipation allowed.
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0
Four Layers PCB
TO-263S-5
25
50
75
100
125
Ambient Temperature (°C)
Figure 3. Derating Curve for RT9009 Package
www.richtek.com
8
DS9009-01 April 2011
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