SARA-R4 series - System Integration Manual
UBX-16029218 - R06
Design-in
Page 75 of 102
2.12
Thermal guidelines
The module operating temperature range is specified in
SARA-R4 series
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 Battery Life Measurement and Current Consumption Technique
however the application should be correctly designed to cope with it.
During transmission at maximum RF power the SARA-R4 series 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 board and connect each ground area of
the multilayer application board 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 device.
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 proper application hardware
design, the increase of module temperature can be moderated by proper application software implementation:
Enable power saving configuration using the AT+CPSMS command
Enable module connected-mode for a given time period and then disable it for a time period enough long to
properly mitigate temperature increase.
