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Modem COM port is so slow, and cannot up to 100Mbpss, the uplink requirements of LTE. So it is not
suggested. The Modem COM can be used to initiate data services temporarily only while the client`s NCM
port is useless.
5.4.2 Application for USB Interface
The recommended circuit design as follows:
T101 and T102 shall choose the TVS pipes witch less than 1pF.
VUSB supply power has connected within the module, so the VBUS pin of Host end can float.
USB_D+ and USB_D- is high speed differential signal line , the highest transmit speed is up to480Mbps.
Not the following requirements while PCB Layout:
USB_DP+ and USB_D- signal lines request with the same length, parallel, and try to avoid right
angle routing.
Around the USB_DP +and USB_D- signal lines should be packaged with GND.
Put the USB2.0 differential signal lines in the signal layer while are nearest to the ground.
USB signal lines shall far away from strong interference signals, like power supply.
Do the impedance matching, the impedance requests 90 ohm.
5.5 USIM Interface
L831-EA wireless module supports USIM and high speed SIM card, and does not supports 8-wire smart
USIM yet.
L831-EA Module Hardware User Manual
Figure5- 6 Recommended circuit design of USB interface
Page 29 of 43
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