User Guide

22／35
In order to enhance the reliability and availability of the USIM card, please pay attention to
these key points:
1. The USIM socket should be placed near the USIM interface and it is recommend that PCB
circuit connecting the USIM interface to the USIM socket does not exceed 200 mm.
2. Keep USIM card signal cable away from RF antenna and module power cable.
3. The decouple capacitor of USIM_VDD should be less than 1uF and placed near the USIM socket.
4. To avoid the mutual interference between USIM_DATA and USIM_CLK, keep them away with
each other and shield them with surrounded ground including USIM_RST.
5. In order to ensure ESD protection in good performance, it is recommended to place the TVS
with stray capacitance of less than 50pF near USIM card socket.
6. It is recommended to connect the 0Ω resistors to USIM_CLK, USIM_DATA and USIM_RST to
avoid EMI interference and enhance ESD protection. Meanwhile, connecting the 33pF
capacitor in parallel to filter interference from EGSM900 RF signals, and keep these
components close to the USIM card socket.
7. USIM_DATA is pulled up internally, which is good for improving the anti-jamming capability.
When the PCB circuit of USIM card is too long or the interference is nearby, the pull-up resistor
is recommended to be placed close to the USIM socket.
3.6 USB Interface
The Pin definition of the M3B module USB interface is as below.
Table 8 Definition of the USB interface
Pin No.
Pin Name
Pad Type Description Comment
36 USB_DM IO
USB differential data
bus(minus)
Require differential
impedance of 90ohm
38 USB_DP IO
USB differential data
bus(positive)
Require differential
impedance of 90ohm
The M3B module is compliant with USB 2.0 High Speed Mode (480Mbps) and Full Speed Mode
12Mbps). And only can be used as slave device. The USB interface is mainly for AT commands, data
Figure 6 shows the circuit of the USB interface
transfer, catch log, and soft w are upgrade.
uCloudlink M3B Mini PCIe-C _Hardware Design Guide_V1.0