RT9481 datasheet(22/41 Pages) RICHTEK

22 / 41 page

RT9481

is a registered trademark of Richtek Technology Corporation.

www.richtek.com

DS9481-00 June 2015

Thermal Considerations

For continuous operation, do not exceed absolute

maximum junction temperature. The maximum power

dissipation depends on the thermal resistance of the IC

package, PCB layout, rate of surrounding airflow, and

difference between junction and ambient temperature.

The maximum power dissipation can be calculated by

the following formula :

PD(MAX) = (TJ(MAX)  TA) / JA

where TJ(MAX) is the maximum junction temperature,

TA is the ambient temperature, and JA is the junction to

ambient thermal resistance.

For recommended operating condition specifications,

the maximum junction temperature is 125

C. The

junction to ambient thermal resistance,

JA, is layout

dependent. For WQFN-24L 4x4 package, the thermal

resistance,

JA, is 28C /W on a standard JEDEC 51-7

four-layer thermal test board. The maximum power

dissipation at TA = 25C can be calculated by the

following formula :

PD(MAX) = (125C  25C) / (28C /W) = 3.57W for

WQFN-24L 4x4 package

The maximum power dissipation depends on the

operating ambient temperature for fixed TJ(MAX) and

thermal resistance,

JA. The derating curve in Figure 5

allows the designer to see the effect of rising ambient

temperature on the maximum power dissipation.

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

100

125

Ambient Temperature (°C)

Four-Layer PCB

Figure 5. Derating Curve of Maximum Power

Dissipation

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