The USBO1_EN and USBO1_OC# signals are only used when the OTG port is operating in host
mode (Micro-A USB connector is plugged in or the port is configured by software as host only). The
USBO1_EN signal is used to enable the USB bus power supply if it needs to be switchable. A USB
compliant design needs to detect overcurrent on the USB bus power supply and switch the power
off should an over-current condition occur. The USBO1_OC# signal is used to signal to the host
controller that an over-current condition has occurred. This signal is active-low and requires a pull-
up resistor on the baseboard.
Figure 21: USB 3.0 OTG reference schematic
The reference schematic for the USB 3.0 OTG is compliant with the USB 3.0 specifications. In the
specifications, there can be found the following cable assemblies:
USB 3.0 Standard-A to USB 3.0 Standard-B Cable (RX and TX crossed in the cable)
USB 3.0 Standard-A to USB 3.0 Micro-B Cable (RX and TX crossed in the cable)
USB 3.0 Micro-A to USB 3.0 Micro-B Cable (RX and TX crossed in the cable)
USB 3.0 Micro-A to USB 3.0 Standard-B Cable (RX and TX crossed in the cable)
Adapter cables such as from Micro-A plug to a Standard-A socket (known as OTG cables) are not
in the specifications. Nevertheless, the cable assemblies above imply that the OTG cable need to
have the RX and TX lines strait (not crossed). Unfortunately, there are USB 3.0 OTG cables on the
market that crosses the RX and TX lines. These cables are not compatible with the reference
schematic. Only OTG cables that are not crossing the SuperSpeed signals are compatible. The
non-compatible adapter cables often are promoted as OTG cables for the Samsung Galaxy Note 3
cellphone. The Micro-A plug of these cables also have a wrong shape. They are shaped as Micro-B
plug even though it is a Micro-A plug.
2.5.2.2 USB 2.0 Client Schematic Example
If the USBO1 port is used only as high-speed client interface (e.g. if only used as debugging
interface), a simplified schematic diagram is necessary.
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