User's Manual

LE910 Hardware User Guide

1vv0301089 Rev.3 – 09-06-2014

The thermal design for the power supply heat sink should be done with the following

specifications:

 Average current consumption during HSPA transmission @PWR level max in LE910:

640mA (TBD)

 Average current consumption during class12 GPRS transmission @PWR level max:

680mA (TBD)

 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 by the network. The average current consumption hence varies

significantly.

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 LE910, 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 LE910; you must ensure that your application can dissipate heat.

In the WCDMA/HSPA mode, since LE910 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 LE910 which you will mount. You must mount LE910 on the large

ground area of your application board and make many ground vias to dissipate the heat.