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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 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 UE910, you can consider it to be during transmission 1W max

during CSD/VOICE calls and 2W max during class12 GPRS upload.

This generated heat will be mostly conducted to the ground plane under the UE910; you must

ensure that your application can dissipate it.

DRAFT

Telit Wireless Solutions UE910 series User Manual

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