User's Guide
LE920A4 HW User Guide Power Supply
Doc#: 1VV0301261 General Design Rules
Rev. 4.7.1 Page 60 of 124 2019-11-21
NOTE:
The thermal design for the power supply must be made keeping an average
consumption at the maximum transmitting level during calls of
LTE/HSPA/GPRS plus average consumption in GPS Tracking mode.
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 an Active Call or Data session.
For the heat generated by the module, consider it to be 2W max during transmission at
Class12 GPRS upload for LE920A4-EU and LE920A4-CN variants / Class10 GPRS
transmission for LE920A4-NA. The generated heat is mostly conducted to the ground
plane under the module. Ensure that your application can dissipate heat.
In LTE/WCDMA/HSPA mode, the module 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 module is
mounted on a large ground area of the application board, with many ground vias available
beneath the module for effective heat dissipation.
Even though peak current consumption in GSM mode is higher than in
LTE/WCDMA/HSPA, considerations for heat sink are more important in the case of
WCDMA due to the continuous transmission conditions.
6.2.3. 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
is crucial for the correct operation of the circuitry. A misplaced component can be useless
or can even decrease the power supply performances.
The bypass low ESR capacitor must be placed close to the module power input
pads, or if the power supply is a switching type, it can be placed close to the
inductor to cut the ripple, as long as the PCB trace from the capacitor to module is
wide enough to ensure a drop-less connection even during the 2A current peaks.
The protection diode must be placed close to the input connector where the power
source is drained.
The PCB traces from the input connector to the power regulator IC must be wide
enough to ensure no voltage drops occur during the 2A current peaks.
Note that this is not done to save power loss but especially to avoid the voltage
drops on the power line at the current peaks frequency of 216 Hz that will reflect
on all the components connected to that supply (also introducing the noise floor at
the burst base frequency.)