In section 16.3.7 of the Technical Reference Manual it states:
Upon the USB controller determining its role as a host, it will drive the USBx_DRVVBUS pin high to
enable the external power logic so that it start sourcing the required 5V power (must be ≥ 4.4V but to
account for the voltage drop on the cable it is suggested to be in the neighborhood of 4.75V). The USB2.0
controller will then wait to for the voltage of the USBx_VBUSIN to go high. Upon sampling a little time
later, if it does not see the voltage on the USBX_VBUSIN pin to be within a Vbus Valid range (>= 4.4V), it
will generate a Vbus error interrupt.
Is the definition of "a little time" specified anywhere? Or even an order of magnitude (ns / us / ms / seconds)?
We understand that from a previous posting by Paul Eaves
http://e2e.ti.com/support/dsp/sitara_arm174_microprocessors/f/791/p/197987/705709.aspx#705709
that if 5V is applied to the VBUS pin too early, the USB PHY will automatically switch into device mode. But if we take more than "a little time" in applying 5V to VBUS, the PHY will generate an error. So there's obviously a critical time window there to succeed in entering host mode.
We are creating a test board where this timing may have some significance. Is "a little time" defined anywhere? I couldn't find any timing diagrams whatsoever for USB in the AM335x datasheet.
Thanks.
