User's Manual

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RST USIM_RESET 18 Reset signal
VCC VREG_EXTUSIM 21 USIM card power
GND GND 7, 8, 13, 14, 16, 19, 22, 26, 27,
30, 36, 40, 42, 47, 55, 59
GND
2.2.4.2 Reference circuit
The reference circuit of USIM interface is shown in Figure 2-8 below.
1) The DATA line of USIM is connected to SIM power supply by a pull-up resistor with reference value 15KΩ.
2) To avoid the instantaneous voltage overflowing, the resistor with reference value 22Ω can be used for the DATA,
CLK and RST line. Just like the resistors R307, R308 and R309 in Figure 2-8.
3) To avoid the static electricity in USIM socket, it is recommended to use the ESD protection device for the DATA，
CLK and VCC line. Just like the varistors RV301, RV302, RV303 and RV304 in figure 2-8 which should be close
to the USIM socket as possible.
4) To get more flat USIM power supply, it is recommended to use the filter capacitors. Just like C311 and C312 in
Figure 2-8 with reference value 33pF and 100nF.
5) To eliminate the peak interference and high frequency interference signal on RST and CLK line, the filter capacities
(C310, C309) can be placed in RST and CLK line, the reference value is 33pF.
Figure 2-8 The reference circuit of USIM interface