User's Manual

CL865-DUAL Hardware User Guide
1vv0301104 Rev.1 – 2014-03-07
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Reserved. Page 29 of 70
Mod. 0805 2011-07 Rev.2
6.3.5. Thermal Design Guidelines
The thermal design for the power supply heat sink must be done with the following
specifications:
Average current consumption during CDMA 1x @PWR level max : 620mA
NOTE:
The average consumption during transmissions depends on the power level at which the
device is requested to transmit via the network. The average current consumption hence varies
significantly.
Considering the very low current during idle, especially if the Power Saving function is
enabled, it is possible to consider from the thermal point of view that the device absorbs
current significantly only during calls.
If we assume that the device stays in transmission for short periods of time (a few minutes)
and then remains for quite a long time in idle (one hour), then the power supply always has
time to cool down between the calls and the heat sink could be smaller than the calculated for
620mA maximum RMS current. There could even be a simple chip package (no heat sink).
Moreover in average network conditions the device is requested to transmit at a lower power
level than the maximum and hence the current consumption will be less than 620 mA (usually
around 300 mA).
For these reasons the thermal design is rarely a concern and the simple ground plane where
the power supply chip is placed can be enough to ensure a good thermal condition and avoid
overheating.
The heat generated by the CL865 must be taken into consideration during transmission at
24.5dBm max during calls. This generated heat will be mostly conducted to the ground plane
under the CL865. The application must be able to dissipate heat.
In the CDMA 1x mode, since CL865 emits RF signals continuously during transmission,
special attention must be paid to how to dissipate the heat generated.
The current consumption will be up to about 620mA in CDMA 1x continuously at the
maximum TX output power (24.5dBm). Thus, you must arrange the area on the application
PCB must be as large as possible under CL865.
The CL865 must be mounted on the large ground area of the application board and make
many ground vias to dissipate the heat.