RT5002 datasheet(36/40 Pages) RICHTEK

36 / 40 page

RT5002

DS5002-00

November 2011

www.richtek.com

Figure 4. Derating Curves for RT5002 Package

0.00

0.40

0.80

1.20

1.60

2.00

2.40

2.80

3.20

100

125

Ambient Temperature (

°C)

Four-Layer PCB

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) / θJA

where TJ(MAX) is the maximum junction temperature, TA is

the ambient temperature, and

θJAis the junction to ambient

thermal resistance.

For recommended operating condition specifications of

the RT5002, the maximum junction temperature is 125

°C

and TA is the ambient temperature. The junction to ambient

thermal resistance,

θJA, is layout dependent. For WQFN-

40L 5x5 packages, the thermal resistance,

θJA, is 36°C/

W on a standard JEDEC 51-7 four-layer thermal test board.

The maximum power dissipation at T

= 25

°C can be

calculated by the following formula :

PD(MAX) = (125

°C − 25°C) / (36°C/W) = 2.778W for

WQFN-40L 5x5 package

The maximum power dissipation depends on the operating

ambient temperature for fixed TJ(MAX) and thermal

resistance,

θJA. For the RT5002 package, the derating

curve in Figure 4 allows the designer to see the effect of

rising ambient temperature on the maximum power

dissipation.

Layout Considerations

For the best performance of the RT5002, the following

PCB layout guidelines must be strictly followed.

}

Place the input and output capacitors as close as

possible to the input and output pins respectively for

good filtering.

}

Keep the main power traces as wide and short as

possible.

}

The switching node area connected to LX and inductor

should be minimized for lower EMI.

}

Place the feedback components as close as possible

to the FB pin and keep these components away from

the noisy devices.

}

Connect the GND and Exposed Pad to a strong ground

plane for maximum thermal dissipation and noise

protection.

}

The connection of RISETA should be isolated from other

noisy traces. A short wire is recommended to prevent

EMI and noise coupling.

RT5002 Datasheet(PDF) 36 Page - Richtek Technology Corporation

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