Integration Manual

LISA-U2 series - System Integration Manual
UBX-13001118 - R25 Design-In Page 131 of 182
Further hardware techniques to be used to improve 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 and dissipated over the
backside of the application board
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 to 1.5 ÷ 3.5 °C/W. The effect of lower Rth,M-A can be seen from the module
temperature increase, which now can be summarized as following:
 1.5°C during a GSM voice call at max TX power
 3°C during GPRS data transfer with 4 TX slots at max TX power
 2.5°C during EDGE data transfer with 4 TX slots at max TX power
 5.5°C in UMTS/HSxPA connection at max TX power
Beside the reduction of the Module-to-Ambient thermal resistance implemented by the hardware
design of the application device integrating a LISA-U2 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 (GERAN / UTRA), 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 (see the module
temperature increase values summarized above) by means of an AT command (see the u-blox AT
Commands Manual [2], +COPS command)
 Select the operating band which provides lower current consumption in the selected radio access
mode (see current consumption values reported in the LISA-U2 series Data Sheet [1]) by means of
an AT command (see the u-blox AT Commands Manual [2], +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