Kontron COMe Starterkit Eval T2 - Manual (Page 82)

COM Express Interfaces
Signal Pins T6 Pins T10 Description I/O
USB_SSRX3+ C13 USB Port 3, SuperSpeed RX + I PCIE
USB_SSRX3- C12 USB Port 3, SuperSpeed RX - I PCIE
2.9.1.1. USB Differential lines (USB[0:3/1]+/-)
These signals fully comply to the USB 2.0 implementation and are described in chapter 2.8.1
'Signal Definitions' on page 76 above.
2.9.1.2. USB Over-Current Protection (USB_x_y_OC#)
The USB Specification describes power distribution over the USB port, which supplies power for
USB devices that are directly connected to the Carrier Board. Therefore, the host must
implement over-current protection on the ports for safety reasons. Should the aggregate current
drawn by the downstream ports exceed a permitted value, the over-current protection circuit
removes power from all affected downstream ports. The over-current limiting mechanism must
be resettable without user mechanical intervention. For more detailed information about this
subject, refer to the 'Universal Serial Bus Specifications Revision 2.0', which can be found on the
website http://www.usb.org.
Over-current protection for USB ports can be implemented by using power distribution switches
on the Carrier Board that monitor the USB port power lines. Power distribution switches usually
have a soft-start circuitry that minimizes inrush current in applications where highly capacitive
loads are employed. Transient faults are internally filtered.
Additionally, they offer a fault status output that is asserted during over-current and thermal
shutdown conditions. These outputs should be connected to the corresponding COM Express
Modules USB over-current sense signals. Fault status signaling is an option at the USB
specification. If you don't need the popup message in your OS you may leave the signals
USB_0_1_OC#, USB_2_3_OC#, USB_4_5_OC# and USB_6_7_OC# unconnected.
Fault status signals are connected by a pullup resistor to VCC_3V3_SBY on COM Express
Module. Please check your tolerance on a USB port with VCC_5V supply.
USB 2.0 port's VCC current limit should be set to 500mA. For USB 3.0 implementations, the
VCC current limit is raised to 1A. A different, USB 3.0 compatible, power switch is used.
PICMG ® COM Express ® Carrier Board Design Guide Rev. 2.0 / December 6, 2013
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