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RT9017

500mA Peak, Thermal Folded Back CMOS LDO Regulator

Richtek Technology 

Preliminary

RT9017

For continuous operation, do not exceed absolute

maximum operation junction temperature 125°C. The

power dissipation definition in device is :

PD = (VIN − VOUT) x IOUT + VIN x IQ

The maximum power dissipation depends on the thermal

resistance of IC package, PCB layout, the rate of

surroundings airflow and temperature difference between

junction to ambient. The maximum power dissipation can

be calculated by following formula :

PD(MAX) = ( TJ(MAX) - TA ) / θJA

Where TJ(MAX) is the maximum operation junction

temperature 125°C, TA is the ambient temperature and the

θJA is the junction to ambient thermal resistance.

For recommended operating conditions specification of

RT9017, where TJ(MAX) is the maximum junction

temperature of the die (125°C) and TA is the maximum

ambient temperature. The junction to ambient thermal

resistance (θJA is layout dependent) for SOT-23-3/SOT-

23-5 package is 250°C/W and WDFN-6L 2x2 package is

165°C/W on standard JEDEC 51-3 thermal test board.

The maximum power dissipation at TA = 25°C can be

calculated by following formula :

PD(MAX) = (125°C−25°C)/250 = 400 mW (SOT-23-3/

SOT-23-5)

PD(MAX) = (125°C−25°C)/333 = 300 mW (SC-70-5)

The maximum power dissipation depends on operating

ambient temperature for fixed TJ(MAX) and thermal

resistance θJA. For RT9017 packages, the Figure 3. of

derating curves allows the designer to see the effect of

rising ambient temperature on the maximum power

allowed.

700

WDFN-6L 2x2

600

500 SOT-23-3/

SOT-23-5

400

300

200

100

0

0

25

50

75

100 125 150

Ambient Temperature (°C)

Figure 3. Derating Curve for Packages

DS9017-03 August 2007

www.richtek.com

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