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CMPWR101

250 mA SmartOR Regulator with VAUX Switch

ON Semiconductor 

CMPWR101

PERFORMANCE INFORMATION (Cont’d)

CMPWR101 Typical Thermal Characteristics

The overall junction to ambient thermal resistance (qJA)

for device power dissipation (PD) consists primarily of two

paths in series. The first path is the junction to the case (qJC)

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:

TJUNC + TAMB ) PD(qJC) ) PD(qCA)

+ TAMB ) PD(qJA)

The CMPWR101 uses a standard SOIC package. When

this package is mounted on a double−sided printed circuit

board with two square inches of copper allocated for “heat

spreading”, the resulting qJA is 85°C/W.

Based on a maximum power dissipation of 0.43 W

(1.7 V x 250 mA) with an ambient of 70°C, the resulting

junction temperature will be:

TJUNC + TAMB ) PD(qJA)

+ 70° C ) 0.4 W (80° CńD)

+ 70° C ) 37° C + 103° C

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 (5 mA). This allows the ambient temperature to

be representative of the internal junction temperature.

NOTE:

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 CMPWR101 with

an overall qJA of 100°C/W which allows up to

500 mW to be safely dissipated.

Figure 13. Regulator VOUT vs. TAMB (250 mA Load)

Figure 14. Deselect Threshold vs. TJUNCT

Figure 15. Switch Resistance vs. Ambient

Temperature

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