CM3107
Performance Information (cont’d)
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
)
When a CM3107-00SN (SOIC) 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 85°C, the available power of
this package will be:
P
D
= (150°C -85°C) / 151°C/W = 0.43W
For the CM3107-00SB (PSOP), the
θ
JA
is 40°C/W and
the available power for this package will be:
P
D
= (150°C -85°C) / 40°C/W = 0.1.625W
DDR Memory Application
Since the output voltage is 1.25V, and the device can
either source current from VDDQ or sink current to
Ground, the power dissipated in the device at any time
is 1.25V times the current load. This means the maxi-
mum average RMS current (in either direction) is
0.344A for CM3107-00SN and 1.3A for CM3107-00SB.
The maximum instantaneous current is specified at 2A,
so this condition should not be exceeded 17% and
65% of the time for CM3107-00SN and CM3107-00SB,
respectively. It is highly unlikely in most usage of DDR
memory 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 PD can be 0.73W
for CM3107-00SN and 2.75W for CM3107-00SB. So
the maximum average RMS current increases from
0.42A to 0.58A for CM3107-00SN and maximum
© 2004 California Micro Devices Corp. All rights reserved.
instantaneous current of 2A should not be exceeded
29% of the time. For CM3107-00SB, the maximum
RMS current increases from 1.3A to 2.2A. Thus, the
maximum continuous current can be 2A all the time.
Figure 12. Duty Cycle vs. Ambient
Temperature (I
LOAD
= 2A)
Figure 13. Duty Cycle vs. Output
Current (Temp=70°C)
8
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L
Tel: 408.263.3214
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www.calmicro.com
02/02/04
CALMIRCO [ CALIFORNIA MICRO DEVICES CORP ]
