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Behavior of downstream VBUS based on ACA-Dock and ghost charge features in HX3.
ACA - Dock
ON if devices connected to any of DS ports.
OFF if no devices in DS ports.
If no devices in DS ports, hub will be in suspend mode.
Hub in suspend mode.
Connected (Alive/Shut Down)
DS power ON always if US port connected to host.
Case I: No ACA-Dock and ghost charge feature
When the host is powered down, the hub will detect VBUS disconnect from the Upstream (US) port. The VBUS of Downstream (DS_VBUS) ports will be turned OFF. Even if the host is alive and there is no communication, the hub will be idle and the DS_VBUS will be turned OFF.
Case II: Ghost charge feature is enabled
In this case, DS_VBUS is turned OFF and turned ON after 500 ms. The ghost charging feature enables charging of USB devices connected on the DS ports even if the upstream port is not connected to the host.
Case III: ACA-Dock feature is enabled
In this case, the US_VBUS is always connected to the 5-V local supply rather than to VBUS from host. As per the USB specification, the ACA-Dock feature is implemented based on the ID line. If the ID line is sensed, the hub should always provide the power to the host device (mobile/tablet). Even if the host tablet/mobile is shut down, the ID line is still connected to the hub, so the hub cannot turn OFF the US_VBUS. Eventually, the DS_VBUS cannot be turned OFF by the hub.
To turn OFF the DS_VBUS, the host tablet/mobile should be unplugged to disconnect the ID line, which results in turning OFF the DS_VBUS.