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FIBOCOM NL668-LA Series Hardware Guide
Page 34 of 61
USIM_CLK and USIM_DATA signals are ground isolated to avoid mutual interference. If it is difficult
to do so, (U)SIM signal needs to be ground protected as a set;
The filter capacitor and ESD device of (U)SIM card signal cable should place close to the (U)SIM
card connector.
Please select equivalent capacitor is 22pF to 33pF for ESD device.
USIM_DATA should pull up to USIM_VDD with a 10K resistor.
5.4 USB Interface
5.4.1 USB Pin Definition
NL668-LA series module support USB2.0, compatible with USB High-Speed(480Mbits/s) and USB
Full-Speed(12Mbits/s). module USB bus timing and electrical characteristics refer to
Universal Serial Bus
Specification 2.0
.
Table 5-9 USB pin definition
Pin name
I/O
Pin No.
Description
USB_DP
IO
69
USB differential data bus D+
USB_DM
IO
70
USB differential data bus D-
USB_VBUS
PI
71
USB Plug detect
For more information about the USB 2.0 specification, please refer to
Note:
Since the module supports USB 2.0 High-Speed, TVS tube equivalent capacitance on the
USB_DM/DP differential signal cable is required to be less than 1pF, and a 0.5pF capacitance
TVS is recommended.
Connect a 0
Ω
resistor to USB_DM / DP differential line to help analyze problems.
USB_DM and USB_DP are high-speed differential signal cables, can achieve the maximum
transmission rate of 480Mbits/s, and must follow the rules below in PCB Layout:
USB_DM and USB_DP signal cable’s control differential impedance is 90Ω.
USB_DM and USB_DP signal cables shall be parallel and equal in length, and avoid the
right-angle route.
USB_DM and USB_DP signal cables are routed on the signal layer closest to the ground
layer, and the cables shall be grounded.
