User's Manual

SARA-G3 and SARA-U2 series - System Integration Manual
UBX-13000995 - R08 Objective Specification Design-in
Page 141 of 188
2.12 Thermal guidelines
SARA-G3 and SARA-U2 series module operating temperature range and module thermal resistance are
specified in the SARA-G3 series Data Sheet [1] or the SARA-U2 series Data Sheet [2].
The most critical condition concerning module thermal performance is the uplink transmission at maximum
power (data upload or voice call 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; however the application should be correctly designed to cope with it.
During transmission at maximum RF power the SARA-G3 modules generate thermal power that can exceed 1 W,
whereas the SARA-U2 modules generate thermal power that can exceed 2 W: these are indicative values since
the exact generated power strictly depends on operating condition such as the cellular radio access technology,
the number of allocated TX slot, the transmitting frequency band, etc. The generated thermal power must be
adequately dissipated through the thermal and mechanical design of the application, in particular for SARA-U2
modules when operating in the 3G cellular radio access technology.
SARA-U2 modules implement an integrated self protection algorithm when operating in the 3G cellular
radio access technology: the module reduces the transmitted power when the temperature internally
sensed in the integrated 3G Power Amplifier approaches the maximum allowed junction temperature, to
guarantee device functionality and long life span.
The spreading of the Module-to-Ambient thermal resistance (Rth,M-A) depends on 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.
Mounting a SARA-G3 module on a 79 mm x 62 mm x 1.41 mm 4-Layers PCB with a high coverage of copper in
still air conditions
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, the increase of the module temperature
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in different modes of operation, referred to idle
state initial condition
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, can be summarized as following:
 ~8 °C during a GSM voice call (1 TX slot, 1 RX slot) at max TX power
 ~12 °C during a GPRS data transfer (2 TX slots, 3 RX slots) at max TX power
The Module-to-Ambient thermal resistance value and the relative increase of module temperature will be
different for other mechanical deployments of the module, e.g. PCB with different dimensions and
characteristics, mechanical shells enclosure, or forced air flow.
The increase of thermal dissipation, i.e. the Module-to-Ambient thermal resistance reduction, will decrease the
temperature for internal circuitry of the SARA-G3 and SARA-U2 series modules for a given operating ambient
temperature. This improves device long-term reliability for applications operating at high ambient temperature.
A few hardware techniques may be used to reduce the Module-to-Ambient thermal resistance 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 via stack 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
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Refer to SARA-G3 and SARA-U2 series Data Sheet [1] for the Rth,M-A value in this application condition
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Temperature is measured by internal sensor of cellular module
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Steady state thermal equilibrium is assumed. The module’s temperature in idle state can be considered equal to ambient temperature