CMPWR280TO datasheet(9/10 Pages) CALMIRCO

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215 Topaz Street, Milpitas, California 95035

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CALIFORNIA MICRO DEVICES

CMPWR280

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 CMPWR280TO is housed in a TO-263 5-lead package,

which provides a θ

JC of 3°C/W. The ground tab is soldered

down to the PCB. When the device is mounted on a double

sided printed circuit board with two square inches of copper

allocated for heat spreading, the resulting θ

JA is 25°C/W.

Typical Thermal Characteristics

Based on a maximum power dissipation of 2.85W

(1.9Vx1.5A) with an ambient of 70°C the resulting junction

temperature will be:

JUNC = TAMB + PJUNC (θJA )

= 70°C + 2.85W (25°C/W)

= 70°C + 71°C = 141°C

All thermal characteristics of the CMPWR280TO 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 CMPWR280TO with an overall θ

JA of 25°C/W

which allows up to 2.5W 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 25mV.

Fig 3.1. Output Voltage vs. Temperature

3.260

3.280

3.300

3.320

3.340

100

125

Junction Temperature [° C]

5mA load

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