CM3196
Performance Information (cont’d)
Typical Thermal Characteristics
The overall junction to ambient thermal resistance
instantaneous current of 2A should not be exceeded
29% of the time. For CM3196-12SB, the maximum
RMS current increases from 1.3A to 2.2A. Thus, the
maximum continuous current can be 2A all the time.
(θJA) for device power dissipation (P ) consists prima-
D
rily of two paths in series. The first path is junction to
case (θJC) which is defined by the package style, and
the second path is case to ambient (θCA) 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
= T + P (θJC) + P (θCA
)
JUNC
A
D
D
= T + P (θJA)
A
D
When a CM3196-12SN (SOIC) is mounted on a dou-
ble-sided printed circuit board with two square inches
of copper allocated for "heat spreading," the resulting
θJA 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 = (150°C -85°C) / 151°C/W = 0.43W
D
For the CM3196-12SB (PSOP), θJA is 40°C/W and the
available power for this package will be:
Figure 10. Duty Cycle vs. Ambient
P = (150°C -85°C) / 40°C/W = 1.625W
D
Temperature (I
= 2A)
LOAD
DDR Memory Application
Since the output voltage is 1.25V, and the device can
either source current from V or sink current to
DD
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 CM3196-12SN and 1.3A for CM3196-12SB.
The maximum instantaneous current is specified at 2A,
so this condition should not be exceeded 17% and
65% of the time for CM3196-12SN and CM3196-12SB,
respectively. It is highly unlikely in the use of DDR
memory that this would 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 ) can be 0.73W
D
Figure 11. Duty Cycle vs. Output
for CM3196-12SN and 2.75W for CM3196-12SB. So
the maximum average RMS current increases from
0.42A to 0.58A for CM3196-12SN and maximum
Current (Temp=70°C)
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9
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