USB VBUS shows One volt even when nothing connected

RE: USB VBUS shows One volt even when nothing connected

Simonr — Mon, 03 Feb 2020 11:35:12 GMT

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

RE: USB VBUS shows One volt even when nothing connected

OwainIncus — Fri, 31 Jan 2020 14:46:22 GMT

We have checked the USB Enable register the complex should not be enabled; yet we still see around a volt.
In addition to the schematic I have uploaded; the isensetek module only has the nordic recommended cap to ground on the VBUS signal.

RE: USB VBUS shows One volt even when nothing connected

OwainIncus — Fri, 31 Jan 2020 14:44:13 GMT

RE: USB VBUS shows One volt even when nothing connected

Simonr — Fri, 31 Jan 2020 13:00:43 GMT

Hi Owain

Is there any load between the USB connector and the nRF52840? If not, it is likely that there will be a low voltage present when the USB connector isn't in use. Alternatively (if you haven't already), you can try implementing the USB power detect event so that the USB disables when it is not connected to the connector to see if that helps.

Best regards,

Simon