LISA-U2 series - System Integration Manual
UBX-13001118 - R19
Early Production Information
Design-In
Page 126 of 175
2.3
Thermal guidelines
LISA-U2 module operating temperature range and module thermal resistance are specified in the
LISA-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; however the application should be correctly designed to cope with it.
During transmission at maximum RF power the LISA-U2 modules generate thermal power that can exceed 2 W:
this is an indicative value since the exact generated power strictly depends on operating condition such as the
number of allocated TX slot and modulation (GMSK or 8PSK) or data rate (WCDMA), 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 (R
th,M-A
) depends on the module operating
condition (e.g. 2G or 3G mode, transmit band): 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 LISA-U2 module on a 90 mm x 70 mm x 1.46 mm 4-Layers PCB with a high coverage of copper in
still air conditions
7
, the increase of the module temperature
8
in different modes of operation, referred to idle
state initial condition
9
, can be summarized as following:
7°C during a GSM voice call at max TX power
19°C during GPRS data transfer with 4 TX slots at max TX power
16°C during EDGE data transfer with 4 TX slots at max TX power
25°C in UMTS/HSxPA connection at max TX power
The Module-to-Ambient thermal resistance value and the related 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 LISA-U2 modules for a given operating ambient temperature. This improves
the device long-term reliability 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 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
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
7
Refer to
LISA-U2 series Data Sheet
[1] for the R
th,M-A
value in this application condition
8
Temperature is measured by internal sensor of wireless module
9
Steady state thermal equilibrium is assumed. The module’s temperature in idle state can be considered equal to ambient temperature
