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L830-EB Hardware User Manual Page 22 of 39
3.4 USB Interface
The L830 module supports USB 2.0 which is compatible with USB High-Speed (480 Mbit/s) and USB
Full-Speed (12 Mbit/s). For the USB timing and electrical specification of L830 module, please refer to
“Universal Serial Bus Specification 2.0” .
3.4.1 USB Interface Definition
3.4.2 USB Interface Application
The reference circuit is shown in Figure 3-11:
Figure 3-11 Reference Circuit for USB 2.0 Interface
Since the module supports USB 2.0 High-Speed, it is required to use TVS diodes with equivalent
capacitance of 1pF or smaller ones on the USB_D-/D+ differential signal lines, it is recommended to use
0.5pF TVS diodes.
USB_D- and USB_D+ are high speed differential signal lines with the maximum transfer rate of 480 Mbit/s,
so the following rules shall be followed carefully in the case of PCB layout:
USB_D- and USB_D+ signal lines should have the differential impedance of 90 ohms.
USB_D- and USB_D+ signal lines should be parallel and have the equal length, the right angle
routing should be avoided.
USB_D- and USB_D+ signal lines should be routed on the layer that is adjacent to the ground
layer, and wrapped with GND vertically and horizontally.
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