User's Manual

GE/GC864-QUAD V2 and GE864-GPS Hardware User Guide
1vv0300915 Rev.2 – 2011-06-15
Reproduction forbidden without Telit Communications S.p.A. written authorization - All Rights
Reserved. Page 43 of 97
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 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 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,
hence the current consumption will be less than 500mA, 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
grants a good thermal condition to avoid overheating as well.
As far as the heat generated by GC/GE864-QUAD V2 and GE864-GPS
, you can consider it to be during transmissions of 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 GC/GE864-QUAD V2 AND GE864-GPS ; you must ensure
that your application can dissipate it.
6.3.3. 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 GE/GC864-QUAD V2 and GE864-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 GE/GC864-QUAD V2 and
GE864-GPS 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