User's Manual

HE910 Hardware User Guide

1vv0300925 Rev.9 – 07-02-2012

5.3.2 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

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 HE910, 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 HE910; you

must ensure that your application can dissipate it.