SMARC T335x Carrier Board Hardware Design Guide, Document Revision 1.2
2.3.2.2. EMI/ESD Protection
To improve the
EMI
behavior of the USB interface, a design should
include common mode chokes, which have to be placed as close as
possible to the USB connector signal pins. Common mode chokes can
provide required noise attenuation but they also distort the signal quality of
full-speed and high-speed signaling. Therefore, common mode chokes
should be chosen carefully to meet the requirements of the
EMI
noise
filtering while retaining the integrity of the USB signals on the carrier board
design.
To protect the USB host interface of the module from over-voltage caused
by electrostatic discharge (
ESD
) and electrical fast transients (
EFT
), it is
highly recommended to use low capacitance steering diodes and transient
voltage suppression diodes that must be implemented on the carrier
board (for example
PACDN006MR
ESD
Suppressor from On
Semiconductor or
SR05
RailClamp®' surge rated diode arrays from
Semtech,
http://semtech.com
).
Figure 13: USB EMI/ESD Protection