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Curious issue at VBUS-Power Pin "USB_OTG2_VBUS"

Question asked by Walter Wolfgang on Apr 12, 2017
Latest reply on Apr 21, 2017 by Walter Wolfgang

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