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The overall junction to ambient thermal resistance
Output Voltage Change vs. Temperature (1mA Load)
(θJA) for device power dissipation (PD) consists prima-
50
40
rily of two paths in series. The first path is the junction
to the case (θJC) which is defined by the package style,
30
and the second path is case to ambient (θCA) thermal
20
resistance which is dependent on board layout. The
final operating junction temperature for any set of con-
ditions can be estimated by the following thermal equa-
tion:
10
0
-10
-20
-30
-40
-50
TJUNC = TAMB + PD ∗ (θJC) + PD ∗ (θCA
= TAMB + PD ∗ (θJA)
)
The CM3014 uses a SOT23-5 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 θJA is 175°C/W.
-50 -25
0
25
50
75 100 125
TEMPERATURE [oC]
Based on a maximum power dissipation of 320mW
(Load x Vin-Vout = 150mA x 2.2V) with an ambient of
70°C the resulting junction temperature will be:
Ground Current vs. Temperature
100
80
60
40
20
0
TJUNC = TAMB + PD ∗ (θJA)
= 70°C + 315mW ∗ (175°C/W)
= 70°C + 57.75°C = 127.75°C
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Measurements showing performance up to a junction
temperature of 125°C were performed under light load
conditions (1mA). This allows the ambient temperature
to be representative of the internal junction tempera-
ture.
0
25
50
75
100
125
JUNCTION TEMPERATURE [oC]
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 typically provide the CM3014 with
an overall θJA of 175°C/W, which allows up to 450mW
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to be dissipated safely.
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2002 California Micro Devices Corp. All rights reserved.
8
430 N. McCarthy Blvd., Milpitas, CA 95035-5112
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Tel: 408.263.3214
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Fax: 408.263.7846
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www.calmicro.com
12/13/02
CALMIRCO [ CALIFORNIA MICRO DEVICES CORP ]
