Integration Manual

TOBY-L2 and MPCI-L2 series - System Integration Manual
UBX-13004618 - R04 Advance Information Design-in
Page 115 of 141
2.14 Thermal guidelines
Modules’ operating temperature range is specified in TOBY-L2 Data Sheet [1] and MPCI-L2 Data Sheet [2].
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; however the application should be correctly designed to cope with it.
During transmission at maximum RF power the TOBY-L2 and MPCI-L2 series modules generate thermal power
that can exceed 3 W: this is an indicative value since the exact generated power strictly depends on operating
condition such as the number of allocated TX resource blocks, 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 (Rth,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.
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 thermal via stacked down to main ground layer.
 Use the two mounting holes described in Figure 66 to fix (ground) the MPCI-L2 modules to the main ground
of the application board with suitable screws and fasteners.
 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.
 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.
 Follow the thermal guidelines for integrating wireless wide area network mini card add-in cards, such as the
MPCI-L2 series modules, as provided in the PCI Express Mini Card Electromechanical Specification [14]
For example, the Module-to-Ambient thermal resistance (Rth,M-A) is strongly reduced with forced air ventilation
and a heat-sink installed on the back of the application board, decreasing the module temperature variation.
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 module connected-mode for a given time period and then disable it for a time period enough long to
properly mitigate temperature increase.