LTE Standard Module Series
EC21_Series_Hardware_Design
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Module
USIM_VDD
USIM_GND
USIM_RST
USIM_CLK
USIM_DATA
0R
0R
0R
100 nF
(U)SIM Card Connector
33 pF 33 pF 33 pF
VCC
RST
CLK IO
VPP
GND
15K
USIM_VDD
Figure 18: Reference Circuit of (U)SIM Interface with a 6-pin (U)SIM Card Connector
To enhance the reliability and availability of the (U)SIM card in customers’ applications, please follow the
criteria below in (U)SIM circuit design:
Keep placement of (U)SIM card connector to the module as close as possible. Keep the trace length
as less than 200 mm as possible.
Keep (U)SIM card signals away from RF and VBAT traces.
Make sure the bypass capacitor between USIM_VDD and USIM_GND less than 1 μF, and place it
as close to (U)SIM card connector as possible. If the ground is complete on customers’ PCB,
USIM_GND can be connected to PCB ground directly.
To avoid cross-talk between USIM_DATA and USIM_CLK, keep them away from each other and
shield them with surrounded ground.
For better ESD protection, it is recommended to add a TVS diode array whose parasitic capacitance
should not be more than 15 pF. The 0 Ω resistors should be added in series between the module
and the (U)SIM card to facilitate debugging. The 33 pF capacitors are used for filtering interference
of EGSM900. Please note that the (U)SIM peripheral circuit should be close to the (U)SIM card
connector.
The pull-up resistor on USIM_DATA trace can improve anti-jamming capability when long layout
trace and sensitive occasion are applied, and should be placed close to the (U)SIM card connector.
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