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CMPWR300SA

500mA SmartOR™ DUAL REGULATOR WITH V AUX SWITCH

California Micro Devices Corp 

CALIFORNIA MICRO DEVICES

CMPWR300

Typical Thermal Characteristics

Thermal dissipation of junction heat consists primarily of

two paths in series. The first path is the junction to the case

(θJC) thermal resistance which is defined by the package style,

and the second path is the case to ambient (θCA) thermal

resistance, which is dependent on board layout.

The overall junction to ambient (θJA) thermal resistance is

equal to:

θJA = θJC + θCA

For a given package style and board layout, the operating

junction temperature is a function of junction power

dissipation PJUNC, and the ambient temperature, resulting in

the following thermal equation:

TJUNC = TAMB + PJUNC (θJC ) + PJUNC (θCA )

= TAMB + PJUNC (θJA )

Based on a maximum power dissipation of 1.0W (2Vx500mA)

with an ambient of 70°C the resulting junction temperature

will be:

TJUNC = TAMB + PJUNC (θJA )

= 70°C + 1.0W (50°C/W)

= 70°C + 50°C = 120°C

All thermal characteristics of the CMPWR300SA were

measured using a double sided board with two square inches

of copper area connected to the GND pins for “heat

spreading”.

Measurements showing performance up to junction

temperature of 125°C were performed under light load

conditions (5mA). This allows the ambient temperature to

be representative of the internal junction temperature.

The CMPWR300SA is housed in a thermally enhanced

package where the GND pins (5 through 8) are integral to

the leadframe (fused leadframe). When the device is mounted

on a double sided printed circuit board with two square

inches of copper allocated for “heat spreading”, the resulting

θJA is 50°C/W.

Note: The use of multi-layer board construction with power

planes will further enhance the thermal performance of the

package. In the event of no copper area being dedicated for

heat spreading, a multi-layer board construction will typically

provide the CMPWR300SA with an overall θJA of 70°C/W

which allows up to 780mW to be safely dissipated.

Fig 3.1. Output Voltage vs. Temperature.

This shows the regulator VOUT performance up to the

maximum rated junction temperature. The overall 125°C

variation in junction temperature causes an output voltage

change of about 30mV.

©2000 California Micro Devices Corp. All rights reserved.

10

215 Topaz Street, Milpitas, California 95035

Tel: (408) 263-3214

Fax: (408) 263-7846

www.calmicro.com

12/5/2000

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