LEXI-R422 - System integration manual
UBX-23007449 - R02
Design-in
Page 83 of 108
C1-Public
2.11
Thermal guidelines
☞
The module operating temperature range is specified in the LEXI-R422 data sheet
The most critical condition concerning module thermal performance is the uplink transmission at
maximum power (data upload in connected mode), when the baseband processor runs at full speed,
radio circuits are all active and the RF power amplifier is driven to higher output RF power. This
scenario is not often encountered in real networks (for example, see the Terminal Tx Power
distribution for WCDMA, taken from operation on a live network, described in the GSMA TS.09 Official
Document
); however the application should be correctly designed to cope with it.
During transmission at maximum RF power the LEXI-R422 modules generate thermal power that may
exceed 0.5 W: this is an indicative value since the exact generated power strictly depends on operating
condition such as the actual antenna return loss, the transmitting frequency band, etc. The generated
thermal power must be adequately dissipated through the thermal and mechanical design of the
application.
The spreading of the Module-to-Ambient thermal resistance (R
th,M-A
) depends on the module
operating condition. The overall temperature distribution is influenced by the configuration of the
active components during the specific mode of operation and their different thermal resistance
toward the case interface.
☞
The Module-to-Ambient thermal resistance value and the relative increase of module temperature
will differ according to the specific mechanical deployments of the module, e.g. application PCB
with different dimensions and characteristics, mechanical shells enclosure, or forced air flow.
The increase of the thermal dissipation, i.e. the reduction of the Module-to-Ambient thermal
resistance, will decrease the temperature of the modules internal circuitry for a given operating
ambient temperature. This improves the device long-term reliability in particular for applications
operating at high ambient temperature.
Recommended hardware techniques to be used to improve heat dissipation in the application:
•
Connect each
GND
pin with solid ground layer of the application PCB and connect each ground
area of the multilayer application PCB with complete thermal via stacked down to main ground
layer.
•
Provide a ground plane as wide as possible on the application board.
•
Optimize antenna return loss, to optimize overall electrical performance of the module including a
decrease of module thermal power.
•
Optimize the thermal design of any high-power components included in the application, such as
linear regulators and amplifiers, to optimize overall temperature distribution in the application.
•
Select the material, the thickness and the surface of the box (i.e. the mechanical enclosure) of the
application device that integrates the module so that it provides good thermal dissipation.
Beside the reduction of the Module-to-Ambient thermal resistance implemented by correct
application hardware design, the increase of module temperature can be moderated by a
correspondingly correct application software implementation:
•
Enable power saving configuration using the +CPSMS AT command
•
Enable module connected mode for a given time period and then disable it for a time period long
enough to adequately mitigate the temperature increase.
