SARA-G3 and SARA-U2 series - System Integration Manual
UBX-13000995 - R26
Design-in
Page 162 of 217
2.12
Thermal guidelines
SARA-G3 and SARA-U2 series modules operating temperature range and thermal data are specified in the
SARA-G3 series Data Sheet
[1] or the
SARA-U2 series Data Sheet
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 (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 [18]); 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, with the exception of SARA-U201, 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 internal temperature, to guarantee device functionality and long life span.
The spreading of the Module-to-Ambient thermal resistance (R
th,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
47
, the increase of the module temperature
48
in different modes of operation, referred to idle
state initial condition
49
, 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 are
application dependent, according to the specific mechanical deployment of the module, e.g. application
PCB dimensions and characteristics, mechanical shells enclosure and air flow conditions.
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.
47
Refer to
SARA-G3 series
Data Sheet
[1] for the R
th,M-A
value in this application condition
48
Temperature is measured by internal sensor of cellular module
49
Steady state thermal equilibrium is assumed. The module’s temperature in idle state can be considered equal to ambient temperature
