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[AM1808] Is USB0_VBUS connection required when always attached?

TimHarron
Mastermind 18130 points
Other Parts Discussed in Thread: AM1808

We are using the AM1808 in device/peripheral mode, as an embedded (self-powered, always connected) device. In such a configuration, do we still need to bring in 5V from the host into the AM1808's USB0_VBUS pin? Since we don't have to do a "connection detection" because we're always attached, I thought maybe this would not be required.  If it's just a sense pin, I was curious if it can be asserted in firmware without the actual 5V brought in. My thought is that this pin is still required for the hardware to 'detect' rather than the firmware but I wanted to double-check.

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    TI__Genius 14545 points

    Tim,

       Is there a reason why you need to skip VBUS? It is used for sensing the valid VBUS level, and is often used to determine if the D+/D- pull Ups / pull downs should be active / not active to prevent back powering to the Host.

       I would recommend bring in the VBUS is possible, especially since it's only one pin / trace. You can override the role of the OTG PHY (device / or host) in the System Configuration Guide which means you can operate as Host/Dev without sensing the VBUS, but it's useful to sense in general as an extra feedback pin.