CMPWR300 datasheet(10/11 Pages) CALMIRCO

10 / 11 page

CALIFORNIA MICRO DEVICES

12/5/2000

215 Topaz Street, Milpitas, California 95035

Tel: (408) 263-3214

Fax: (408) 263-7846

www.calmicro.com

CMPWR300

Thermal dissipation of junction heat consists primarily of

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

(θ

JC) thermal resistance which is defined by the package style,

and the second path is the case to ambient (θ

CA) thermal

resistance, which is dependent on board layout.

The overall junction to ambient (θ

JA) thermal resistance is

equal to:

JA = θJC + θCA

For a given package style and board layout, the operating

junction temperature is a function of junction power

dissipation P

JUNC, and the ambient temperature, resulting in

the following thermal equation:

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

= T

AMB + PJUNC (θJA )

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

JA is 50°C/W.

Typical Thermal Characteristics

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

with an ambient of 70°C the resulting junction temperature

will be:

JUNC = 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.

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 θ

JA of 70°C/W

which allows up to 780mW to be safely dissipated.

Fig 3.1. Output Voltage vs. Temperature.

This shows the regulator V

OUT performance up to the

maximum rated junction temperature. The overall 125°C

variation in junction temperature causes an output voltage

change of about 30mV.

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