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CMPWR330

400mA SmartOR™ Regulator with VAUX Switch

ON Semiconductor 

CMPWR330

Performance Information (cont’d)

CMPWR330 Typical Thermal Characteristics

The overall junction to ambient thermal resistance (θJA) for device power dissipation (PD) consists primarily of

two paths in series. The first path is the junction to the case (θJC) which is defined by the package style, and the

second path is case to ambient (qCA) thermal resistance which is dependent on board layout. The final

operating junction temperature for any set of conditions can be estimated by the following thermal equation:

TJ

= TA + (PD)(θJC) + (PD)(θCA)

= TA + (PD)(θJA)

The CMPWR330 uses a thermally enhanced package where all the GND leads (pins 5 through 8) are integral

to the leadframe. When this package is mounted on a double-sided printed circuit board with two square inches

of copper allocated for "heat spreading", the resulting θJA is about 50°C/W.

Based on a typical operating power dissipation of 0.7W (1.75V x 0.4A) with an ambient of 70°C, the resulting

junction temperature will be:

TJ = TA + (PD)(θJA)

= 70°C + 0.7W X (50°C/W)

= 70°C + 35°C = 105°C

The thermal characteristics were measured using a double-sided board with two square inches of copper area

connected to the GND pin 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 separate ground and power planes will further enhance

the overall thermal performance. In the event of no copper area being dedicated for heat spreading, a multi-

layer board construction, using only the minimum size pad layout, will provide the CMPWR330 with an overall

qJA of 70°C/W which allows up to 780mW to be safely dissipated for the maximum junction temperature.

Rev. 3 | Page 10 of 13 | www.onsemi.com

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