CM3109
Performance Information (cont’d)
Typical Thermal Characteristics (cont’d)
Front Side Bus Application
If the CM3109-00SB/SH is instead used for the Front
Side Bus application, where V
DDQ
could be connected
to the 3.3V V
CC
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.
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 [2.75W / 1.9V] =
1.45A. If this average current is exceeded, the device
will go over-temperature and the output will drop to 0V.
The theoretical calculations of these relationships
show the safe operating area of the CM3109 in the
PSOP package.
Thermal characteristics were measured using a double
sided board with two square inches of copper area
connected to the GND pins for "heat spreading".
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.
Figure 15. Output Voltage vs. Ambient
Temperature (I
LOAD
=5mA)
Figure 14. Reference Voltage vs. Temperature
Figure 16. Quiescent Current vs. Temperature
©
2004 California Micro Devices Corp. All rights reserved.
01/15/04
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