CMPWR280

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9

TYPICAL THERMAL CHARACTERISTICS

Thermal dissipation of junction heat consists primarily of

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

(

style, and the second path is the case to ambient (

thermal resistance, which is dependent on board layout.

The overall junction to ambient (

is equal to:

For a given package style and board layout, the operating

junction temperature is a function of junction power

the following thermal equation:

The CMPWR280TO is housed in a TO−263 5−lead

package, which provides a

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

25C/W.

Based on a maximum power dissipation of 2.85 W

(1.9 V x 1.5 A) with an ambient of 70C the resulting

junction temperature will be:

+ 70° C ) 2.85 W (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 (5 mA). 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

of 25C/W which allows up to 2.5 W to be

safely dissipated.

Output Voltage vs. Temperature. Output Voltage vs.

the maximum rated junction temperature. The overall 125C

variation in junction temperature causes an output voltage

change of about 25 mV.

Figure 19. Output Voltage vs. Temperature

Output Voltage (Rated) vs. Temperature. Output

Voltage (Rated) vs. Temperature shows the regulator steady

state performance when fully loaded (1.5 A) in an ambient

temperature up to the rated maximum of 70C. The output

variation at maximum load is approximately 13 mV across

the normal temperature range.

Figure 20. Output Voltage (Rated) vs. Temperature