LISA-U2 series - System Integration Manual
UBX-13001118 - R19
Early Production Information
System description
Page 50 of 175
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
the application board providing a proper 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 properly 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 an High
logic level will be re-applied on the
GPIO5
pin. (For more details see section 1.12 and to 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 proper 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 proper 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 SIM requirements.
Connect the contacts C1 (VCC) and C6 (VPP) of the two UICC / SIM to the
VSIM
pin of the module by
means of a proper 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 proper
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
proper 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
proper 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 µs is
the maximum allowed rise time on the
SIM_IO
and
SIM_RST
lines).
