PRELIMINARY
CM3018
Performance Information (cont’d)
Typical Thermal Characteristics
The overall junction to ambient thermal resistance (θ
JA
)
for device power dissipation (P
D
) consists primarily of
two paths in series. The first path is the junction to the
case (θ
JC
) which is defined by the package style, and
the second path is case to ambient (θ
CA
) thermal resis-
tance 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
∗
(θ
JC
) + P
D
∗
(θ
CA
)
= T
AMB
+ P
D
∗
(θ
JA
)
SOT-23 Package Considerations
When the SOT23 version of the CM3018 is mounted
on a double-sided printed circuit board with two square
inches of copper allocated for "heat spreading", the
resulting
θ
JA
is 175°C/W.
OUTPUT CHANGE [mV]
Ground Current vs. Temperature
(VIN=5V)
GROUND CURRENT [uA]
100
80
60
40
20
0
0
25
50
75
o
100
125
TEMPERATURE [ C]
Output Voltage Change vs. Temperature
(VIN=5V, 1mA Load)
50
40
30
20
10
0
-10
-20
-30
-40
-50
-50
-25
0
25
50
TEMPERATURE [ C]
o
Based on a maximum power dissipation of 320mW
(Load x V
IN
-V
OUT
= 150mA x 2.2V) with an ambient of
70°C the resulting junction temperature will be:
T
JUNC
= T
AMB
+ P
D
∗
(θ
JA
)
= 70°C + 315mW
∗
(175°C/W)
= 70°C + 57.75°C = 127.75°C
Thermal characteristics 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 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.
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
CM3018
in a
SOT23 package with an overall
θ
JA
of 175°C/W, which
allows up to 450mW to be dissipated safely.
Please consult CAMD Technical Support for assistance
with thermal analysis of the CM3018 with respect to a
specific application.
75
100 125
©
2004 California Micro Devices Corp. All rights reserved.
07/29/04
430 N. McCarthy Blvd., Milpitas, CA 95035-5112
▲
Tel: 408.263.3214
▲
Fax: 408.263.7846
▲
www.calmicro.com
9
CALMIRCO [ CALIFORNIA MICRO DEVICES CORP ]
