Telit Wireless Solutions HE910-EU V2, Руководство пользователя по оборудованию

Страница: 35 / 78


A protection diode must be inserted close to the power input, in order to save
HE910 V2 from power polarity inversion. Otherwise the battery connector must
be done in a way to avoid polarity inversions when connecting the battery.

The battery capacity must be at least 500mAh in order to withstand the current
peaks of 2A; the suggested capacity is from 500mAh to 1000mAh.
The thermal design for the power supply heat sink must be done with the following
specifications:

Average current consumption during HSPA transmission @PWR level max in
HE910 V2: 640mA

Average current consumption during class10 GPRS transmission @PWR level
max: 390mA

Average current consumption during class33 GPRS transmission @PWR level
max: 600mA

Average GPS current during GPS ON (Power Saving disabled) : 65mA
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)/600mA(class33 GPRS)
/390mA(class10 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)/ 600mA (class33 GPRS)/ 390mA (class10 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)
/ 600mA (class33 GPRS) /390mA (class10 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 HE910 V2, you can consider it to be during transmission 2W
max during class10 GPRS/class33 GPRS upload. This generated heat will be mostly