Smart Machine Smart Decision
SIM868_Series_Hardware_Design_V1.06 38 2017-07-13
Module
PRESENCE
100nF
MOLEX-91228
SIM
Card
22pF
VCC
GND
RST
VPP
CLK I/O
GND
VDD_EXT
SIM_VDD
SIM_RST
SIM_CLK
SIM_DATA
4.7K
ESDA6V1
SIM_DET
22R
22R
22pF
22R
22pF
Figure 30: Reference circuit of the 8-pin SIM card holder
The SIM_DET pin is used for detection of the SIM card hot plug in. Customer can select the 8-pin SIM card
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 Figure 31.
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
22R
22R
22pF
22R
22pF
Figure 31: Reference circuit of the 6-pin SIM card holder
5.8.2. SIM Card Design Guide
SIM card signal could be interfered 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, GSM_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
Recommend to place a 100nF capacitor on SIM_VDD line and keep it close to the SIM card holder
Add some TVS with parasitic capacitance should not exceed 50pF
Add 22R resistors 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
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