LISA-U series - System Integration Manual
UBX-13001118 - R17
Advance information
Design-In
Page 139 of 190
2.2.3
Placement
Optimize placement for minimum length of RF line and closer path from DC source for
VCC
.
Make sure that RF and analog circuits are clearly separated from any other digital circuits on the system board.
Provide enough clearance between the module and any external part due to solder and paste masks design.
Milled edges that are present at module PCB corners, away from module pins metallization, can slightly increase
module dimensions from the width and the height described in the mechanical specifications sections of
LISA-U1
series Data Sheet
[1] and
LISA-U2 series Data Sheet
[2]: provide enough clearance between module PCB corners
and any other external part mounted on the application board.
The heat dissipation during continuous transmission at maximum power can significantly raise the
temperature of the application base-board below the LISA-U modules: avoid placing temperature sensitive
devices (e.g. GNSS receiver) close to the module.
2.3
Thermal guidelines
LISA-U module operating temperature range and module thermal resistance are specified in the
LISA-U1
series Data Sheet
[1] and
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-U 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-U 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
14
, the increase of the module temperature
15
in different modes of operation, referred to idle state
initial condition
16
, 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.
14
Refer to
LISA-U1 series Data Sheet
[1] and
LISA-U2 series Data Sheet
[2] for the R
th,M-A
value in this application condition
15
Temperature is measured by internal sensor of wireless module
16
Steady state thermal equilibrium is assumed. The module’s temperature in idle state can be considered equal to ambient temperature
