CMPWR101
http://onsemi.com
6
PERFORMANCE INFORMATION (Cont’d)
CMPWR101 Typical Thermal Characteristics
The overall junction to ambient thermal resistance (q
JA
)
for device power dissipation (P
D
) consists primarily of two
paths in series. The first path is the junction to the case (q
JC
)
which is defined by the package style, and the second path
is case to ambient (q
CA
) 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:
T
JUNC
+ T
AMB
) P
D
(q
JC
) ) P
D
(q
CA
)
+ T
AMB
) P
D
(q
JA
)
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:
T
JUNC
+ T
AMB
) P
D
(q
JA
)
+ 70° C ) 0.4W(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 q
JA
of 100°C/W which allows up to
500 mW to be safely dissipated.
Figure 13. Regulator V
OUT
vs. T
AMB
(250 mA Load)
Figure 14. Deselect Threshold vs. T
JUNCT
Figure 15. Switch Resistance vs. Ambient
Temperature
