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CMPWR280 Datasheet PDF : 10 Pages
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CALIFORNIA MICRO DEVICES
CMPWR280
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 )
The CMPWR280TO is housed in a TO-263 5-lead package,
which provides a θJC 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 θJA is 25°C/W.
Based on a maximum power dissipation of 2.85W
(1.9Vx1.5A) with an ambient of 70°C the resulting junction
temperature will be:
TJUNC = 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 θJA 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 VOUT performance up to the maximum rated
junction temperature. The overall 125°C variation in junction
temperature causes an output voltage change of about 25mV.
3.340
Fig 3.1. Output Voltage vs. Temperature
3.320
3.300
5mA load
3.280
3.260
0
25
50
75
100
125
Junction Temperature [° C]
© 2000 Calirornia Micro Devices Corp. All rights reserved.
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215 Topaz Street, Milpitas, California 95035 Tel: (408) 263-3214 Fax: (408) 263-7846 www.calmicro.com
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