Integration Manual

TOBY-L2 and MPCI-L2 series - System Integration Manual
UBX-13004618 - R26 Design-in
Page 126 of 162
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
(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 [17]); 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
may exceed 3 W: this is an indicative value since the exact generated power strictly depends on operating condition
such as the actual antenna return loss, the number of allocated TX resource blocks, 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 (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.
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.
 Use the two mounting holes described in Figure 70 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.
 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 [16].
Further hardware techniques that may be considered to improve the heat dissipation in the application:
 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 of the TOBY-L2 series LGA modules and dissipated over the
backside of the application board.
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.