User's Manual

UE866 HARDWARE USER GUIDE 1vv0301157 Rev.7 • 2015-04-17 22 of 68

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 : 700 mA

 Average current during idle: 1.8 mA

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 700mA

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 700mA, 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.

The generated heat will be mostly conducted to the ground plane under the UE866; you must ensure

that your application can dissipate it.

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.