Curious issue at VBUS-Power Pin "USB_OTG2_VBUS"

[wowa]

Dear Community,

i have noted a curious issue if i measure the VBUS Power Pin "USB_OTG2_VBUS" . For a better overview please let me introduce the schematic constellation:

"USB_OTG1_VBUS" is connected to the conventional 5V VBUS to a USB Port. "USB_OTG2_VBUS" is supplied with an internal switchable 5V due to a FET. 

If the device is switched on with plugged-in USB Port 1 and corresponding VBUS from PC, at "USB_OTG2_VBUS" Pin i can measure a coupled voltage level from the VBUS from Port 1. If Device is switched off and USB to PC is still connected i can still see the coupled voltage at "USB_OTG2_VBUS". This is an unwanted issue.

Why does it happens ? I thought  "USB_OTG2_VBUS" is only a conventional input power pin....

At moment i have solved the problem while i use a diode that no VBUS from Port 1 is coupling the inernal circuit.

Thanks beforehand for your efforts.

Best regards

Wolfgang Walter

[CarlosCasillas]

Hi Walter,

In this case, you could refer to sections related to USB of the “Hardware Development Guide for i.MX 6Quad, 6Dual, 6DualLite, 6Solo Families of Applications Processors” document at the following link:

http://www.nxp.com/files/32bit/doc/user_guide/IMX6DQ6SDLHDG.pdf

 
Hope this will be useful for you.
Best regards!
/Carlos
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[wowa]

Hi Carlos,

thanks for your answer, but i cannot find something helpfull in the document regarding this issue. It is very curious that i can measure on Pin "USB_OTG2_VBUS" the VBUS from "USB_OTG1_VBUS". It is not exactly the 5 V, there is a little potential difference but i can tell that it is coming from the VBUS on "USB_OTG1_VBUS". Something is happening internal on the LDO for the USB Interface. But i do not know what.

Best regards

Wolfgang