User's Manual

SARA-G3 and SARA-U2 series - System Integration Manual
UBX-13000995 - R08 Objective Specification Design-in
Page 142 of 188
 Optimize the thermal design of any high-power component included in the application, 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
 Force ventilation air-flow within mechanical enclosure
 Provide a heat sink component attached to the module top side, with electrically insulated / high thermal
conductivity adhesive, or on the backside of the application board, below the cellular module, as a large part
of the heat is transported through the GND pads and dissipated over the backside of the application board
Module PCB
Heat-Sink
on application
PCB bottom side
Application PCB
Heat flow over
Module Pads
Application PCB
Heat-Sink
Figure 83: Thermal solution example providing a heat sink on the backside of the application board, below the cellular module
For example, after the installation of a robust aluminum heat-sink with forced air ventilation on the back of the
same application board described above, the Module-to-Ambient thermal resistance (Rth,M-A) is reduced up to
the Module-to-Case thermal resistance (Rth,M-C) defined in the SARA-G3 series Data Sheet [1] or the SARA-U2
series Data Sheet [2].
The effect of lower Rth,M-A due to the installation of a robust heat-sink on the backside of the application board
with forced air ventilation can be seen from the module temperature increase, which now can be summarized as
following for SARA-G3 modules:
 ~1 °C during a GSM voice call (1 TX slot, 1 RX slot) at the maximum TX power
 ~2 °C during a GPRS data transfer (2 TX slots, 3 RX slots) at the maximum TX power
Beside the reduction of the Module-to-Ambient thermal resistance implemented by the hardware design of the
application device integrating a SARA-G3 and SARA-U2 series module, the increase of module temperature can
be moderated by the software implementation of the application.
Since the most critical condition concerning module thermal power occurs when module connected-mode is
enabled, the actual module thermal power depends, as module current consumption, on the radio access mode,
the operating band and the average TX power.
A few software techniques may be implemented to reduce the module temperature increase in the application:
 Select the radio access mode which provides lower temperature increase by means of AT command (see the
u-blox AT Commands Manual [3])
 Select by means of AT command the GPRS multi-slot class which provides lower current consumption (see
current consumption values reported in SARA-G3 series Data Sheet [1] or SARA-U2 series Data Sheet [2],
and u-blox AT Commands Manual [3], +UCLASS command)
 Select by means of AT command the operating band which provides lower current consumption (see current
consumption values reported in SARA-G3 series Data Sheet [1] or SARA-U2 series Data Sheet [2], and u-blox
AT Commands Manual [3], +UBANDSEL 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