User's Manual

GE864- QUAD Har dwar e User Guide

1vv0300872 Rev.1 2010-04-02

NOTE:

The average consumption dur ing 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 cur rent dur ing idle, especially if Power Saving function is

enabled, it is possible to consider from the thermal point of view that the device

absorbs cur rent significantly only dur ing calls.

If we assume that the device stays into tr ansmission for short periods of time (let us

say few minutes) and then remains for a quite long time in idle (let us 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

curr ent, or even could be the simple chip package (no heat sink).

Mor eover in the average networ k conditions the device is requested to transmit at a

lower power level than the maximum and hence the curr ent consumption will be less

than the 500mA, being usually around 150mA.

For these reasons the ther mal design is rarely a concern and the simple ground

plane where the power supply chip is placed can be enough to ensure a good ther mal

condition and avoid overheating.

For the heat gener ated by the GE864-QUAD, you can consider it to be during

transmission 1W max during CSD/VOICE calls and 2W max dur ing class10 GPRS

upload.

This generated heat will be mostly conducted to the ground plane under the GE864-

QUAD; you must ensur e that your application can dissipate it.

6.2.3. Power Supply PCB Layout Guidelines

As seen on the electrical design guidelines the power supply shall have a low ESR

capacitor on the output to cut the curr ent peaks and a protection diode on the input

to protect the supply from spikes and polarity inver sion. The placement of these

components is crucial for the correct working of the circuitr y. A misplaced

component can be useless or can even decrease the power supply performances.

The Bypass low ESR capacitor must be placed close to the Telit GE864-

QUAD power input pads or in the case the power supply is a switching type

it can be placed close to the inductor to cut the ripple provided the PCB

trace fr om the capacitor to the GE864-QUAD is wide enough to ensur e a

dr opless connection even dur ing the 2A current peaks.