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LM940 Hardware Design Guide
1VV0301352 Rev. 18
Page 28 of 75
2022-01-04
Not Subject to NDA
Note: 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 can vary
significantly.types.
Note: The thermal design for the power supply must be made
keeping an average consumption at the maximum transmitting level
during LTE/HSPA data transfer sessions.
Considering the very low current in Idle mode, especially if the Power Saving function is
enabled, it can be assumed that - from the thermal point of view - the device absorbs
significant current only during Data sessions.
In LTE/WCDMA/HSPA mode, the LM940 emits RF signals continuously during
transmission. Therefore, special attention must be paid to dissipate the generated heat.
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.
Note: 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 connected to the output to snub 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 correct circuitry operation. A misplaced component can be
useless or can even decrease the power supply performances.