User Manual

MeiG_SLM550_Hardware Design Manual
MeiG Smart Technology Co., Ltd 69/89
much as possible.
The MIPI interface selects a small-capacity TVS when selecting an ESD device. It is recommended that
the parasitic capacitance be less than 1pF.
⚫ The MIPI routing requirements are as follows:
⚫ The total length of the cable does not exceed 305mm
⚫ It is required to control 100 ohm differential impedance with an error of ±10%.
⚫ The error of the differential line length within the group is controlled within 1mm.
⚫ The length error between groups is controlled within 2 mm.
5.2.5 USB
The module supports high-speed USB interface at a rate of 480Mbps. The user recommends adding a
common-mode inductor during the schematic design phase to effectively suppress EMI interference. If
you need to increase the static protection, please select a TVS tube with a parasitic capacitance of less
than 1pF. Please refer to the following notes when planning Layout:
⚫ The common mode inductor should be close to the side of the USB connector.
⚫ Requires control of 90 ohm differential impedance with an error of ±10%.
⚫ The differential line length error is controlled within 6mm.
⚫ If the USB has a charging function, please note that the VBUS cable is as wide as possible.
⚫ If there is a test point, try to avoid the split line and put the test point on the path of the trace.
Table 16 Internal USB cable length of the module
Pin Signal Length (mm) Length Error (P-N)
14 USB_HS_DP 33.0
0.3mm
13 USB_HS_DM 33.3
5.2.6 Audio
The module supports 3 analog audio signals. Analog signals are susceptible to interference from high
speed digital signals. So stay away from high-speed digital signal lines. The module supports the GSM
system, and the GSM signal can interfere with the audio by coupling and conduction. Users can add
33pF and 10pF capacitors to the audio path to filter out coupling interference. The 33pF capacitor
mainly filters out the interference of the GSM850/EGSM900 band, and the 10pF capacitor mainly filters
out the interference of the DCS1800 band. The coupling interference of TDD has a great relationship
with the PCB design of the user. In some cases, the TDD of the GSM850/EGSM900 frequency band is
more serious, and in some cases, the TDD interference of the DCS1800 frequency band is more
serious. Therefore, the user can select the required filter capacitor according to the actual test result,
and sometimes even do not need to paste the filter capacitor.
The GSM antenna is the main source of coupling interference for TDD, so users should pay attention to
keeping the audio trace away from the GSM antenna and VBAT during PCB layout and routing. The
filter capacitor of the audio is preferably placed close to the module end and placed next to the interface
end. The audio output should be routed according to the differential signal rules.