USB VBUS shows One volt even when nothing connected

[OwainIncus]

Hi,

We are seeing a voltage of approx 1 volt on our USB connector when USB is not being used (VBUS).

We are using our device in a Wet environment; this voltage between GND and VCC on the USB connector is causing us problems in that electrolysis is occurring.
Electrolysis is causing oxidation of USB pins and "probably" eating away the USB connector.

We can fix this in HW by extra protection circuitry; but this requires a respin of our design.

Why are we seeing this parasitic (?) voltage; is it possible to turn this off?

Note we have no requirement to use USB properly, we just use it as a charging interface.

Kind Regards,

Owain

[Simonr]

Hi Owain

I notice that you have an ESD protection component in the USB_VCC net which has an operating voltage of 700mV according to its datasheet. Could it be this voltage you're measuring? If not, I don't see any capacitor between VBUS and ground. You can try adding a resistor between VBUS and ground as well, as that should most likely remove any stray voltage like this.

Best regards,

Simon