SARA-G450 - System integration manual
UBX-18046432 - R08 Design-in Page 89 of 143
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2.5.1.5 Guidelines for dual SIM card / chip connection
Two SIM card / chip can be connected to the modules’ SIM interface as illustrated in the circuit of
Figure 46.
SARA-G450 modules do not support the usage of two SIMs at the same time, but two SIMs can be
populated on the application board providing an appropriate switch to connect only the first SIM or
only the second SIM per time to the SIM interface of the SARA-G450 modules as described in the
Figure 46.
SARA-G450 modules do not support SIM hot insertion / removal: the module is able to properly use a
SIM only if the SIM / module physical connection is provided before the module boot and then held for
normal operation. Switching from one SIM to another one can only be properly done within one of
these two time periods:
After module switch-off by the AT+CPWROFF and before module switch-on by PWR_ON pin
After network deregistration by AT+COPS=2 and before module reset by +CFUN AT command
In the application circuit example represented in Figure 46, the application processor will drive the SIM
switch using its own GPIO to properly select the SIM that is used by the module.
The dual SIM connection circuit described in Figure 46 can be implemented for SIM chips as well,
providing a suitable connection between the SIM switch and SIM chip as described in Figure 44.
If it is required to switch between more than two SIMs, a circuit similar to the one described in the
Figure 46 can be implemented: for example, in the event of a four-SIM circuit, using an appropriate
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 an appropriate low-on resistance (i.e. few ohms) and low-on capacitance (i.e. few pF) 2-throw
analog switch (e.g. Fairchild FSA2567) to ensure high-speed data transfer according to SIM
requirements.
Connect the contact C1 (VCC) of the two UICC / SIM to the VSIM pin of the module by means of an
appropriate 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
an appropriate 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 an appropriate 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 an appropriate 2-throw analog switch (e.g. Fairchild FSA2567).
Connect the contact C5 (GND) of the two UICC / SIM to GND.
Provide a 1 µF bypass capacitor (e.g. Murata GRM155R70J105K) at the SIM supply line (VSIM),
close to the related pad of the two SIM connectors, in order to prevent digital noise.
Provide a bypass capacitor of about 22 pf (e.g. Murata GRM1555C1H220J) 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 1 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 regarding maximum allowed rise time on the lines.
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