Downstream VBUS Behavior Based on ACA_Dock and Ghost Charge Features in HX3 - KBA218374

Version: **

 

Question:

Behavior of downstream VBUS based on ACA-Dock and ghost charge features in HX3.

 

Answer:

 

                                                                                                                                                                                        
   

Sl. No

  
   

ACA - Dock

  
   

Ghost Charge

  
   

Host Status

  
   

Downstream VBUS

  
   

Comments

  
   
        
  1.  
  2.    
  
   

Disabled

  
   

Disabled

  
   

Alive

  
   

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.

  
   
        
  1.  
  2.    
  
   

Disabled

  
   

Disabled

  
   

Shut Down/Disconnected

  
   

OFF

  
   

Hub in suspend mode.

  
   
        
  1.  
  2.    
  
   

Disabled

  
   

Enabled

  
   

Alive

  
   

ON

  
   

 

  
   
        
  1.  
  2.    
  
   

Disabled

  
   

Enabled

  
   

Shut Down/Disconnected

  
   

ON

  
   

 

  
   
        
  1.  
  2.    
  
   

Enabled

  
   

Enabled/Disabled

  
   

Connected (Alive/Shut Down)

  
   

ON

  
   

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.