User's Manual

6.3.2. Thermal Design Guidelines
The thermal design for the power supply heat sink should be done with the following
specifications:
 Average current consumption during transmission @ max PWR level:
500mA
 Average current consumption during transmission @ min PWR level:
150mA
 Average current during Power Saving (CFUN=5) :
2,4mA
 Average current during idle (Power Saving disabled):
24mA
NOTE:
The average consumption during transmissions depends on the power level at which the device
is requested to transmit by the network. The average current consumption hence varies
significantly.
Considering the very low current during idle, especially if 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 into transmission for short periods of time (let's say few
minutes) and then remains for a quite long time in idle (let's say one hour), then the power
supply has always the time to cool down between the calls and the heat sink could be smaller
than the calculated one for 500mA maximum RMS current, or even could be the simple chip
package (no heat sink).
Moreover in the 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 the 500mA, being
usually around 150mA.
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.
For the heat generated by the GE865, you can consider it to be during transmission 1W max
during CSD/VOICE calls and 2W max during class10 GPRS upload.
This generated heat will be mostly conducted to the ground plane under the GE865; you must
ensure that your application can dissipate it.