UL865-N3G Hardware User Guide
1VV0301177 Rev 2– 2015-04-20
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Page 30 of 70
Mod. 0805 2011-07 Rev.2
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 HSDPA transmission @PWR level max :
600
mA
Average current during idle:
1.5
mA
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 600mA 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
600mA, 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 UL865-N3G V2, you can consider it to be during transmission
1W max during CSD/VOICE calls.
This generated heat will be mostly conducted to the ground plane under the UL865-N3G V2;
you must ensure that your application can dissipate it.
