RT9173APM5 datasheet(9/13 Pages) RICHTEK

9 / 13 page

RT9173/A

DS9173/A-18 March 2007

www.richtek.com

Figure 7. The Package Section Drawing of RT9173/A

SOP-8 Package

Figure 8. Thermal Resistance Equivalent Circuit of

RT9173/A SOP-8 Package

The thermal resistance

θJA of IC package is determined by

the package design and the PCB design. However, the

package design has been decided. If possible, it's useful

to increase thermal performance by the PCB design. The

thermal resistance can be decreased efficiently by adding

copper under the main path of thermal flow on the package.

The maximum power dissipation depends on operating

ambient temperature for fixed TJ(MAX) and thermal

resistance

θJA. For RT9173/A package, the Figure 9 and

the Figure 10 show the thermal resistance

θJA vs. copper

area of SOP-8 and TO-263-5 packages on single layer

(1S) and 4-layer (2S2P) thermal test board at TA = 25

°C,

PCB copper thickness = 2oz.

Figure 10. Thermal Resistance

θJA vs. Copper Area of

TO-263-5 Packages

For example, as shown in Figure 9, RT9173/A SOP-8 with

10mm x 10mm cooper area on 4-layers (2S2P) thermal

test board at TA = 25

°C, we can obtain the lower thermal

resistance about 45

°C/W. The power maximum dissipation

can be calculated as :

PD(MAX) = (125

°C - 25°C) / (45 °C/W) = 2.22W (SOP-8)

As shown in Figure 10, RT9173/A TO-263-5 with

15mm x 15mm cooper area on 4-layers (2S2P) thermal

test board at TA = 25

°C, we can obtain the lower thermal

resistance about 29

°C/W. The power maximum dissipation

Ambient

Molding Compound

Gold Wire

Lead Frame

Die Pad

Die

Die Pad

Molding Compound

Lead Frame

Case Point

Junction

DIE

DIE-ATTACH

DIE-PAD

GOLD-LINE

LEAD FRAME

PCB

Ambient

MOLDING-COMPOUND

path 1

path 2

path 3

LEAD FRAME

Internally Fused

θJA vs. Copper Area

100

1020

3040

5060

7080

90 100

Copper Area (mm

SOP-8

2S2P thermal test board

Figure 9. Thermal Resistance

θJA vs. Copper Area of

SOP-8 Packages

Thermal Resistance vs. Cooper Area

100

150

200

250

300

350

400

Cooper Area (mm

TO-263-5

1S thermal test board

2S2P thermal test board

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