Texas Instruments OMAP5912 Reference Manual page 1605

4.11 Conflicts Between USB Signal Multiplexing and Top-Level
Multiplexing
4.12 OMAP5912 USB Hardware Considerations
4.12.1 VBUS Power Switching for USB Type A Host Receptacles
4.12.2 Transient Suppression for USB Connectors
SPRU761A
When OMAP5912 top-level signal multiplexing selects non-USB functionality
for a pin but USB signal multiplexing is set to use that pin as an output, the
signal from the USB signal multiplexing is ignored and the source selected by
the OMAP5912 top-level signal multiplexing is used.
When OMAP5912 top-level signal multiplexing selects non-USB functionality
for a pin but the USB signal multiplexing is set to use that pin as an input, the
OMAP5912 top-level signal multiplexing presents a low level to the USB signal
multiplexer.
It may be useful to select a HMC_MODE value that brings some USB signals
to the OMAP5912 top-level signal multiplexing, but then set the top-level
signal multiplexing to ignore those USB signals.
The USB specification places several VBUS requirements on USB hosts,
including current capability, droop, and other important characteristics.
Circuits that meet the USB specification requirements can be implemented
using
Texas Instruments devices such as the TPS2014 and TSP2015 power
distribution switch devices. Further information, including data sheets and
application notes, can be found at the Texas Instruments web site.
Although an OTG transceiver has the ability to power VBUS within the OTG
specification limits for an OTG dual role device, it may not have sufficient
current sourcing capability to meet the USB 1.1 Specification, which requires
far greater output current on VBUS. If an OTG downstream port must also
support a downstream non-OTG USB device (via a standard-A receptacle to
mini-A plug as defined in the OTG specification), a VBUS switch as mentioned
above can be used to meet those requirements.
It is important to provide transient suppression for USB connectors.
Electrostatic discharge that occurs when a user connects or disconnects a
USB cable can have a dramatic effect on a system if not suppressed. Texas
Instruments offers several devices for transient suppression on USB
connections, such as the SN65220, SN65240, and SN75240 universal serial
bus port transient suppressor devices. Further information, including data
sheets and application notes, can be found at the Texas Instruments web site.
USB OTG Controller
Universal Serial Bus (USB) 313