User's Manual

DE910 Series Hardware User Guide
1vv0300951 Rev.9 – 2015-05-11
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Reserved. Page 32 of 77
 Average GPS current during GPS ON (Power Saving disabled) in DE910 : 55
mA
NOTE:
The average consumption during transmissions depends on the power level at which the
device is requested to transmit via the network. The average current consumption hence varies
significantly.
Considering the very low current during idle, especially if the 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 in transmission for short periods of time (a few minutes)
and then remains for quite a long time in idle (one hour), then the power supply always has
time to cool down between the calls and the heat sink could be smaller than the calculated for
750mA maximum RMS current. There could even be a simple chip package (no heat sink).
Moreover in 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 750mA (usually
around 250 mA).
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.
The heat generated by the DE910 must be taken into consideration during transmission at
24.4dBm max during calls. This generated heat will be mostly conducted to the ground plane
under the DE910. The application must be able to dissipate heat.
In the CDMA 1x/1xEV-DO mode, since DE910 emits RF signals continuously during
transmission, special attention must be paid to how to dissipate the heat generated.
The current consumption will be up to about 750mA in CDMA 1x continuously at the
maximum TX output power (24.4dBm). Thus, you must arrange the area on the application
PCB must be as large as possible under DE910.
The DE910 must be mounted on the large ground area of the application board and make
many ground vias to dissipate the heat.
5.2.6. Power Supply PCB layout Guidelines
As seen in the electrical design guidelines, the power supply must 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 operation of the circuitry. A misplaced component can be useless or can even decrease
the power supply performance.
 The bypass low ESR capacitor must be placed close to the Telit DE910 power
input pads, or if the power supply is a switching type, the capacitor can be placed
close to the inductor to cut the ripple if the PCB trace from the capacitor to