CM3103 Datasheet, PDF (9/10 Pages) California Micro Devices Corp – 400mA SMARTOR REGULATOR Vaux SWITCH

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.
V_OUT Variation with T_AMB (400mA Load)
3.32
3.31
3.30
3.29
3.28
20 30 40 50 60 70
Temperature [^oC]
Select/Deselect Threshold Variation with T_JUNCT
4.55
4.50
4.45
Vselect
4.40
4.35
4.30
4.25
Vdeselect
4.20
25
50 75 100 125 150
Temperature [^oC]
0.37
V_AUX Switch Resistance vs T_AMB
0.35
0.33
0.31
0.29
0.27
0.25
20 30 40 50 60 70
Temperature [^oC]
© 2004 California Micro Devices Corp. All rights reserved.
01/28/04 430 N. McCarthy Blvd., Milpitas, CA 95035-5112 L Tel: [phone] L Fax: [phone] L www.calmicro.com
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