Kontron COMe Starterkit Eval T2 - Manual (Page 78)

COM Express Interfaces
The first schematic is powered from VCC_5V_SBY Suspend power and can provide Wake on
LAN support. The second schematic is powered using 5V.
Power to the USB Port is filtered using a ferrite (90 Ω @100MHz, 3000mA) to minimize
emissions. The ferrite should be placed adjacent to the USB Port connector pins.
USB_0_1_OC# and USB_2_3_OC# are over-current signals that are inputs to COM Express
Module. Each signal is driven low upon detection of overload, short-circuit or thermal trip, which
causes the affected USB Port power to turn off. Do not attach pull-ups to the OC signals on the
COM Express Carrier Board; this is done on the COM Express Module.
The OC# signal is asserted until the over-current or over-temperature condition is resolved.
USB0+/- through USB2+/- from the COM Express Module are routed through a common mode
choke to reduce radiated cable emissions. The part shown is a Coilcraft 0805USB-901MLC; this
device has a common mode impedance of approximately 90 Ω at 100MHz. The common-mode
choke should be placed close to the USB connector.
ESD protection diodes D1 and D2 provide overvoltage protection caused by ESD and electrical
fast transients . Low capacitance diodes and transient voltage suppression diodes should be
placed near the USB connector. The example design uses a SR05 RailClamp surge diode array
DATVSSR05 from Semtech (http://semtech.com).
The example designs show a ferrite connecting Chassis Ground and Logic Ground at the USB
connector. Many USB devices connect Chassis and Logic grounds together. To minimize the
current in this path a ferrite or capacitor connecting Chassis Ground to Logic Ground should be
placed close to the USB connector.
PICMG ® COM Express ® Carrier Board Design Guide Rev. 2.0 / December 6, 2013
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