User's Manual

Telit GE863-GPS

Hardware User guide

1vv0300714, Rev. ISSUE#0, - 21/02/06

For the heat generated by the GE863-GPS, 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 GE863-GPS, you

must ensure that your application can dissipate it.

3.2.3 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 current peaks and a protection diode on the input to protect the supply from

spikes and polarity inversion. The placement of these components is crucial for the correct

working of the circuitry. 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 GE863-GPS 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 from the capacitor to the GE863-GPS is wide

enough to ensure a dropless connection even during the 2A current peaks.

• The protection diode must be placed close to the input connector where the power source is

drained.

• The PCB traces from the input connector to the power regulator IC must be wide enough to

ensure no voltage drops occur when the 2A current peaks are absorbed. Note that this is not

made in order to save power loss but especially to avoid the voltage drops on the power line

at the current peaks frequency of 216 Hz that will reflect on all the components connected to

that supply, introducing the noise floor at the burst base frequency. For this reason while a

voltage drop of 300-400 mV may be acceptable from the power loss point of view, the same

voltage drop may not be acceptable from the noise point of view. If your application doesn't

have audio interface but only uses the data feature of the Telit GE863-GPS, then this noise is

not so disturbing and power supply layout design can be more forgiving.

• The PCB traces to the GE863-GPS and the Bypass capacitor must be wide enough to ensure

no significant voltage drops occur when the 2A current peaks are absorbed. This is for the

same reason as previous point. Try to keep this trace as short as possible.

• The PCB traces connecting the Switching output to the inductor and the switching diode

must be kept as short as possible by placing the inductor and the diode very close to the

power switching IC (only for switching power supply). This is done in order to reduce the

radiated field (noise) at the switching frequency (100-500 kHz usually).

• The use of a good common ground plane is suggested.

• The placement of the power supply on the board should be done in such a way to guarantee

that the high current return paths in the ground plane are not overlapped to any noise

sensitive circuitry as the microphone amplifier/buffer or earphone amplifier.

• The power supply input cables should be kept separate from noise sensitive lines such as

microphone/earphone cables.