User's Manual

LTE Module
EC20 Hardware Design
EC20_Hardware_Design Confidential / Released 35 / 83
If you do not need the USIM card detection function, keep USIM_PRESENCE unconnected. The
reference circuit for using a 6-pin USIM card connector is illustrated as the following figure.
Module
USIM_VDD
USIM_GND
USIM_RST
USIM_CLK
USIM_DATA
22R
22R
22R
100nF
USIM Connector
GND
33pF 33pF 33pF
VCC
RST
CLK IO
VPP
GND
GND
15K
USIM_VDD
Figure 18: Reference Circuit of 6-Pin USIM Connector
In order to enhance the reliability and availability of the USIM card in your application, please follow the
criteria below in the USIM circuit design:
 Keep layout of USIM card as close as possible to the module. Assure the length of the trace is less
than 200mm.
 Keep USIM card signal away from RF and VBAT alignment.
 Assure the ground between module and USIM connector short and wide. Keep the width of ground
and USIM_VDD no less than 0.5mm to maintain the same electric potential.
 To avoid cross-talk between USIM_DATA and USIM_CLK, keep them away with each other and
shield them with surrounded ground.
 In order to offer good ESD protection, it is recommended to add TVS. The 22ohm resistors should be
added in series between the module and the USIM card so as to suppress the EMI spurious
transmission and enhance the ESD protection. The 33pF capacitors are used for filtering interference
of EGSM900. Please note that the USIM peripheral circuit should be close to the USIM connector.
 The pull-up resistor on USIM_DATA line can improve anti-jamming capability when long layout trace
and sensitive occasion is applied, and should be placed close to the USIM connector.