User's Manual

Smart Machine Smart Decision
SIM868_Hardware_Design_V1.00 36 2016-06-20
holder to implement SIM card detection function. AT command “AT+CSDT” is used to enable or disable SIM
card detection function. For details of this AT command, please refer to document [1].
If the SIM card detection function is not used, customer can keep the SIM_DET pin open. The reference circuit
of 6-pin SIM card holder is illustrated in the following figure.
Module
100nF
MOLEX-91228
C107 10M 006 512
22pF
VCC
GND
RST
VPP
CLK I/O
SIM_VDD
SIM_RST
SIM_CLK
SIM_DATA
ESDA6V1
SIM_DET
51O
51O
22pF
51O
22pF
Figure 31: Reference circuit of the 6-pin SIM card holder
4.8.2. SIM Card Design Guide
SIM card signal could be interferenced by some high frequency signal, it is strongly recommended to follow
these guidelines while designing:
 SIM card holder should be far away from GSM antenna
 SIM traces should keep away from RF lines, VBAT and high-speed signal lines
 The traces should be as short as possible
 Keep SIM card holder’s GND connect to main ground directly
 Shielding the SIM card signal by ground well
 Recommended to place a 100nF capacitor on SIM_VDD line and keep close to the SIM card holder
 Add some TVS which parasitic capacitance should not exceed 50pF
 Add 51Ω resistor to (SIM_RST/SIM_CLK/SIM_DATA) signal could enhance ESD protection
 Add 22pf capacitors to (SIM_RST/SIM_CLK/SIM_DATA) signal to reduce RF interference