User's Guide

LM940 HW Design Guide
1VV0301352 Rev. 2 Page 28 of 68 2017-07-19
 Average current consumption during RF transmission @PWR level max in LM940
as shown in Section 4.2, Power Consumption table.
Information – The average consumption during transmission depends
on the power level at which the device is requested to transmit via the
network.
Therefore, the average current consumption varies significantly.
Information – The thermal design for the power supply must be made
keeping an average consumption at the maximum transmitting level
during calls of LTE/HSPA.
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
significant current only during Data session.
In LTE/WCDMA/HSPA mode, the LM940 emits RF signals continuously during
transmission. Therefore, you must pay special attention how to dissipate the heat
generated.
While designing the application board, the designer must make sure that the LM940
module is located on a large ground area of the application board for effective heat
dissipation.
Information – The LM940 must be connected to the ground and metal
chassis of the host board for best RF performance and thermal
dispersion as well as to have module fixed.
 The two holes at the top of the module and the main ground
of the host board must be fastened together.
 The shield cover of the module and the main board of the host
board or the metal chassis of the host device should be
connected with conductive materials.
4.3.3. 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