Telit GE863-QUAD / GE863-PY
Hardware User guide
1vv0300715, Rev. ISSUE#0, - 21/02/06
Reproduction forbidden without Telit Communication written authorization – All Right reserved – Right of modification reserved
page 17 of 71
For the heat generated by the GE863-QUAD/PY, 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-QUAD/PY,
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-QUAD/PY 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-QUAD/PY
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-QUAD/PY, then this
noise is not so disturbing and power supply layout design can be more forgiving.
•
The PCB traces to the GE863-QUAD/PY 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.
