CM3106
Performance Information (cont’d)
Typical Thermal Characteristics (nominal conditions unless otherwise specified)
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
)
When a CM3106-12SN is mounted on a double sided
printed circuit board with two square inches of copper
allocated for "heat spreading", the resulting
θ
JA
is
151°C/W. Based on the over temperature limit of 150°C
with an ambient of 70°C, the available power of this
package will be:
P
D
= (150°C - 85°C) / 151°C/W = 0.43W
Since the
θ
JA
of the CM3106-12SB (PSOP) is 40°C/W,
the available power for this package will be:
P
D
= (150°C - 85°C) / 40°C/W = 1.625W
DDR Memory Application
Since the output voltage is 1.25V, and the device can
either source current from V
DD
or sink current to
Ground, the power dissipated in the device at any time
is 1.25V times the current load. This means the the
maximum average RMS current (in either direction) is
0.344A for the CM3106-12SN and 1.3A for the
CM3106-12SB. The maximum instantaneous current is
specified at 2A, so this condition should not be
exceeded for more than 17% of the time for the
CM3106-12SN and 65% of the time for the CM3106-
12SB. It is highly unlikely in most usage of DDR mem-
ory that this might occur, because it means the DDR
memory outputs are either all high or all low for 17%
(SOIC) and 65% (PSOP) of the time.
If the ambient temperature is 40°C instead of 85°C,
which is typically the maximum in most DDR memory
applications, the power dissipated (P
D
) can be 0.73W,
for the CM3106-12SN and 2.75W for the CM3106-
12SB. So the maximum average RMS current
© 2004 California Micro Devices Corp. All rights reserved.
02/02/04
increases from 0.42A to 0.58A for the CM3106-12SN
and a maximum instantaneous current of 2A should
not be exceeded for more than 29% of the time. For
CM3106-12SB, the maximum RMS current increases
from 1.3A to 2.2A. Thus, the maximum continuous cur-
rent can be 2A all the time.
Figure 10. Duty Cycle vs. Ambient
Temperature (I
LOAD
=2.0A)
Figure 11. Duty Cycle vs. Output
Current (Temp=70°C)
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L
Tel: 408.263.3214
L
Fax: 408.263.7846
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7
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