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LE920 Hardware User Guide
1vv0301026 Rev.0 - draft4 – 2013-05-
Reproduction forbidden without written authorization from Telit Communications S.p.A. - All Rights Reserved.
Page 39 of 76
5.2.2.
Thermal Design Guidelines
The thermal design for the power supply heat sink must be done with the following
specifications:
x
Average current consumption during HSPA transmission @PWR level max in
LE920: 640mA (TBD)
x
Average current consumption during class12 GPRS transmission @PWR level
max: 680mA (TBD)
x
Average GPS current during GPS ON (Power Saving disabled) : 65mA (TBD)
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.
NOTE:
The thermal design for the Power supply must be made keeping an average consumption at
the max transmitting level during calls of 640mA(HSPA)/680mA(GPRS) rms plus 65mA rms
for GPS in tracking mode.
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 in transmission for short periods of time (let us say few
minutes) and then remains for quite a 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 for 640mA (HSPA)/680mA (GPRS) 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 640mA (HSPA)
/680mA (GPRS) (being usually around 250mA).
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.
For the heat generated by the LE920, you can consider it to be during transmission 2W max
during class12 GPRS upload. This generated heat will be mostly conducted to the ground
plane under the LE920; you must ensure that your application can dissipate heat.
In the WCDMA/HSPA mode, since LE920 emits RF signals continuously during
transmission, you must pay special attention how to dissipate the heat generated.
The current consumption will be up to about 640mA in HSPA (630mA in WCDMA)
continuously at the maximum TX output power (23dBm). Thus, you must arrange the PCB
area as large as possible under LE920 which you will mount. You must
mount LE920 on the
large ground area of your application board and make many ground vias to dissipate the heat.
