CM3107
Performance Information (cont’d)
Typical Thermal Characteristics (cont’d)
Front Side Bus Application
If the CM3107-00SN is instead used for the Front Side
Bus application, where VDDQ could be connected to
the 3.3V VCC rail for ease of connectivity, the power
dissipated will increase to [3.3V-1.4V] = 1.9V times the
sourcing current, or [1.4V - 0V] = 1.4V times the sink-
ing current.
Measurements showing performance up to a junction
temperature of 150°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.
So the worst case is with all FSB outputs low for a
period of time, such that the maximum average source
current at an ambient of 40°C is [0.73W / 1.9V] =
0.38A. If this average current is exceeded, the device
will go over-temperature and the output will drop to 0V.
If it is likely that this average current will be exceeded
for the FSB application, then the version with the heat
spreader, CM3107-00SB, should be used, or for com-
monality of device type for both applications, the VDDQ
pin should instead be connected to 2.5V. The maxi-
mum average source current at an ambient of 40°C is
[2.75W/1.9V] = 1.45A.
The theoretical calculations of these relationships
show the safe operating area of the CM3107 in the
SOIC and PSOP packages.
Thermal characteristics were measured using a double
sided board with two square inches of copper area
connected to the GND pins for "heat spreading".
Figure 15. Output Voltage vs. Ambient
Temperature (I
=5mA)
LOAD
Figure 14. Reference Voltage vs. Temperature
Figure 16. Quiescent Current vs. Temperature
Figure 17.
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