Smart Module Series
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4.1.3. USB Interface Design Considerations
Table 12: USB Interface Trace Length Inside the Module (Unit: mm)
To ensure performance, you should follow the following principles when designing USB interfaces:
⚫ Route USB signal traces as differential pairs with surrounded ground. The impedance of USB
differential trace is 90 Ω.
⚫ Route USB differential traces at the inner-layer of the PCB, and surround the traces with ground on
that layer and ground planes above and below. For signal traces, provide clearance from power
supply traces, crystal-oscillators, magnetic devices, sensitive signals like RF signals, analog signals,
and noise signals generated by clock, DC-DC, etc.
⚫ The reference ground plane under the USB signal traces must be continuous without any cuts or vias