Integration Manual

LISA-U2 series - System Integration Manual
UBX-13001118 - R25 System description Page 51 of 182
1.8.1.5 Dual SIM card connection
Two SIM cards / chips can be connected to the module’s SIM interface, as described in the circuit of
Figure 24.
LISA-U2 modules do not support the usage of two SIMs at the same time, but two SIMs can be
populated on an application board that provides a suitable switch to connect only the first SIM or only
the second SIM per time to the SIM interface of the modules as described in Figure 24.
All LISA-U2 series modules support SIM hot insertion / removal on the GPIO5 pin: if the feature is
enabled using the specific AT commands, the switch from first SIM to the second SIM can be cleanly
done when a Low logic level is present on the GPIO5 pin (‘SIM not inserted’ = SIM interface not
enabled), without the necessity of a module re-boot, so that the SIM interface will be re-enabled by
the module to use the second SIM when a High logic level will be re-applied on the GPIO5 pin. (For more
details, see section 1.12 and the u-blox AT Commands Manual [2], +UGPIOC, +UDCONF=50
commands.)
In the application circuit represented in Figure 24, the application processor will drive the SIM switch
using its own GPIO to properly select the SIM that is used by the module. Another GPIO may be used
to handle the SIM hot insertion / removal function of LISA-U2 series modules, which can also be
handled by other external circuits or by the cellular module GPIO according to the application
requirements.
The dual SIM connection circuit described in Figure 24 can be implemented for SIM chips as well,
providing proper connection between SIM switch and SIM chip as described in Figure 22.
If it is required to switch between more than two SIMs, a circuit similar to the one described in Figure
24 can be implemented: for example, in case of four SIM circuits, using a suitable 4-pole 4-throw
switch (or, alternatively, four 1-pole 4-throw switches) instead of the suggested 4-pole 2-throw switch.
Follow these guidelines connecting the module to two SIM connectors:
 Use a suitable low-on resistance (i.e. few ohms) and low-on capacitance (i.e. few pF) 2-throw analog
switch (e.g. Fairchild FSA2567) as SIM switch to ensure high-speed data transfer according to the
SIM requirements.
 Connect the contacts C1 (VCC) of the two UICC / SIM to the VSIM pin of the module by means of a
suitable 2-throw analog switch (e.g. Fairchild FSA2567).
 Connect the contact C7 (I/O) of the two UICC / SIM to the SIM_IO pin of the module by means of a
suitable 2-throw analog switch (e.g. Fairchild FSA2567).
 Connect the contact C3 (CLK) of the two UICC / SIM to the SIM_CLK pin of the module by means
of a suitable 2-throw analog switch (e.g. Fairchild FSA2567).
 Connect the contact C2 (RST) of the two UICC / SIM to the SIM_RST pin of the module by means
of a suitable 2-throw analog switch (e.g. Fairchild FSA2567).
 Connect the contact C5 (GND) of the two UICC / SIM to ground.
 Provide a 100 nF bypass capacitor (e.g. Murata GRM155R71C104K) at the SIM supply line (VSIM),
close to the related pad of the two SIM connectors, to prevent digital noise.
 Provide a bypass capacitor of about 22 pF to 47 pF (e.g. Murata GRM1555C1H470J) on each SIM
line (VSIM, SIM_CLK, SIM_IO, SIM_RST), very close to each related pad of the two SIM connectors,
to prevent RF coupling especially in case the RF antenna is placed closer than 10 - 30 cm from the
SIM card holders.
 Provide a very low capacitance (i.e. less than 10 pF) ESD protection (e.g. Tyco Electronics
PESD0402-140) on each externally accessible SIM line, close to each related pad of the two SIM
connectors, according to the EMC/ESD requirements of the custom application.
 Limit capacitance and series resistance on each SIM signal (SIM_CLK, SIM_IO, SIM_RST) to
match the requirements for the SIM interface (27.7 ns is the maximum allowed rise time on the
SIM_CLK line, 1.0 µ s is the maximum allowed rise time on the SIM_IO and SIM_RST lines).