Quectel EG91 Series Hardware Design page 46

If (U)SIM card detection function is not needed, keep USIM_PRESENCE unconnected. A reference circuit
of (U)SIM interface with a 6-pin (U)SIM card connector is illustrated in the following figure.
USIM_GND
USIM_VDD
USIM_RST
Module
USIM_CLK
USIM_DATA
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 cards in your applications, please follow the
criteria below in the (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 your 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.
 To offer good 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.
EG91_Series_Hardware_Design
USIM_VDD
15K
100 nF
0R
0R
0R
33 pF 33 pF 33 pF
GND
LTE Standard Module Series
(U)SIM Card Connector
VCC
RST
CLK
GND
GND
VPP
IO
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