RT9018A12PSP View Datasheet(PDF) - Richtek Technology

Part Name

Description

Manufacturer

RT9018A12PSP

Maximum 3A, Ultra Low Dropout Regulator

Richtek Technology 

RT9018A/B

PD (MAX) = (125°C − 25°C) / (75°C/W) = 1.33W (SOP-8

Exposed Pad on the minimum layout)

Layout Considerations

The thermal resistance θJA of SOP-8 (Exposed Pad) is

determined by the package design and the PCB design.

However, the package design had been designed. If

possible, it’ s useful to increase thermal performance by

the PCB design. The thermal resistance θJA can be

decreased by adding a copper under the exposed pad of

SOP-8 (Exposed Pad) package.

As shown in Figure 3, 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 3.a), θJA is 75°C/W. Adding

copper area of pad under the SOP-8 (Exposed Pad) Figure

3.b) reduces the θJA to 64°C/W. Even further, increasing

the copper area of pad to 70mm2 (Figure 3.e) reduces the

θJA to 49° C/W.

Figure 3 (d). Copper Area = 50mm2, θJA = 51°C/W

Figure 3 (e). Copper Area = 70mm2, θJA = 49°C/W

Figure 3. Thermal Resistance vs. Different Cooper Area

Layout Design

Figure 3 (a). Minimum Footprint, θJA = 75°C/W

Figure 3 (b). Copper Area = 10mm2, θJA = 64°C/W

The maximum power dissipation depends on operating

ambient temperature for fixed TJ(MAX) and thermal

resistance θJA . For RT9018A/B packages, the Figure 4

of de-rating curves allows the designer to see the effect of

rising ambient temperature on the maximum power

allowed.

2.2

Copper Area

2

70mm2

1.8

50mm2

1.6

30mm2

1.4

1.2

10mm2

Minimum Layout

1

0.8

0.6

0.4

0.2

JEDEC 4-Layers PCB

0

0

20 40 60

80 100 120 140

Ambient Temperature (°C)

Figure 4. De-rating Curves

Figure 3 (c). Copper Area = 30mm2, θJA = 54°C/W

www.richtek.com

10

DS9018A/B-04 September 2007

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