CM3103
Performance Information (cont’d)
CM3103 Typical Thermal Characteristics
The overall junction to ambient thermal resistance
(
θ
JA
) for device power dissipation (P
D
) consists prima-
rily 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
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:
T
JUNC
= T
AMB
+ P
D
(
θ
JC
) + P
D
(
θ
CA
)
= T
AMB
+ P
D
(
θ
JA
)
The CM3103 uses a thermally enhanced package
where all the GND 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
θ
JA
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:
T
JUNC
= T
AMB
+ P
D
(
θ
JA
)
= 70°C + 0.7W X (50°C/W)
= 70°C + 35°C = 105°C
Thermal characteristics were measured using a double-
sided board with two square inches of copper area con-
nected 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 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 provide the CM3103 with an overall
θ
JA
of 70°C/W which allows up to 780mW to be safely
dissipated for the maximum junction temperature.
On Resistance
Ω
]
[
Threshold Voltage [V]
V
OUT
Variation with T
AMB
(400mA Load)
Regulator Output Voltage [V
3.32
3.31
3.30
3.29
3.28
20
30
40
50
o
Temperature [ C]
60
70
Select/Deselect Threshold Variation with T
JUNCT
4.55
4.50
4.45
4.40
4.35
4.30
4.25
4.20
25
50
75
100
125
o
Temperature [ C]
150
Vdeselect
Vselect
V
AUX
Switch Resistance vs T
AMB
0.37
0.35
0.33
0.31
0.29
0.27
0.25
20
30
40
50
o
Temperature [ C]
60
70
© 2004 California Micro Devices Corp. All rights reserved.
01/28/04
430 N. McCarthy Blvd., Milpitas, CA 95035-5112
L
Tel: 408.263.3214
L
Fax: 408.263.7846
L
www.calmicro.com
9
CALMIRCO [ CALIFORNIA MICRO DEVICES CORP ]
