Figure 12: USB Interface Reference Design (OTG Supported)
In order to ensure USB performance, comply with the following principles when designing the USB
interface.
⚫ Route the USB signal traces as a differential pair with total grounding. The impedance of USB
differential trace should be controlled to 90 Ω.
⚫ Keep the ESD protection devices as close as possible to the USB connector. Pay attention to the
influence of junction capacitance of ESD protection devices on USB data lines. Typically, the
capacitance value should be less than 2 pF.
⚫ Do not route signal traces under crystals, oscillators, magnetic devices or RF signal traces. Route the
USB differential traces in inner-layer with ground shielding on not only the upper and lower layers but
also the right and left sides.
⚫ Make sure the trace length difference between USB 2.0 differential data signals is less than 0.7 mm.
Table 13: USB Trace Length Inside the Module
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