RT7257EN Просмотр технического описания (PDF) - Richtek Technology
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RT7257EN Datasheet PDF : 15 Pages
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RT7257E
Preliminary
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 RT7257E packages, the Figure 7 of
derating 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
25
50
75
100
125
Ambient Temperature (°C)
Figure 7. Derating Curves for RT7257E Package
(a) Copper Area = (2.3 x 2.3) mm2, θJA = 75°C/W
(b) Copper Area = 10mm2, θJA = 64°C/W
(c) Copper Area = 30mm2 , θJA = 54°C/W
(d) Copper Area = 50mm2 , θJA = 51°C/W
(e) Copper Area = 70mm2 , θJA = 49°C/W
Figure 6. Themal Resistance vs. Copper Area Layout
Design
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