LISA-U2 series - System integration manual
UBX-13001118 - R27
Design-In
Page 130 of 183
C1-Public
2.3
Thermal guidelines
☞
LISA-U2 module operating temperature range and module thermal parameters 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
9
, the increase of the module temperature
10
in different modes of
operation, referred to idle state initial condition
11
, 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
9
See LISA-U2 series data sheet
for the R
th,M-A
value in this application condition
10
Temperature is measured by internal sensor of wireless module
11
Steady state thermal equilibrium is assumed. The module’s temperature in
idle state can be considered equal to ambient
temperature
