VBUS voltage from 0.5V to 2V

[backstreet.devisor]

Hi.

I am using a custom board on the nRF52820 microcontroller (wiring diagram in the figure). When the microcontroller is powered only from the battery (via external LDO), the VBUS line shows a voltage from 0.5V to 2V.

Can you please tell me why this might be happening?

I have already disconnected all external peripherals from the microcontroller, but the VBUS voltage of at least 0.5V is still present. There is no short circuit on the VBUS line either.

Thanks.

[Bendik Heiskel]

Hi,

The VBUS pin is a input to a internal USB regulator, this regulator is only used for supplying 3.3V used for the USB data lines.

If 5V isn't supplied to the VBUS pin the USB regulator isn't used, in this case the VBUS pin is in a undefined state and the voltage on the pin is undefined.

 

Best regards,

Bendik

[backstreet.devisor]

Hi Bendik. Thank you for your response.

Now it is clear to me why the voltage on VBUS occurs. Before your answer I thought that the voltage on VBUS should be 0V, but I was wrong. 

Then how does this circuitry in the nRF52840DK work to detect a connected USB?

If the VBUS state is undefined, transistor Q40A could open and thus tell the microcontroller that USB is connected?

Or am I wrong?

Thanks.

[backstreet.devisor]

Hi.

Is there any news on this issue? 

In my application, the USB connection needs to be detected. For this purpose I used the schematic from the datasheet of nRF52840DK (schematic in the previous post). But apparently it does not work....

Is there any other way to determine the USB connection?

[Bendik Heiskel]

Hi,

Apologies for the delay.

backstreet.devisor said:

Then how does this circuitry in the nRF52840DK work to detect a connected USB?

The 150k pulldown resistor connected to VBUS in the detect circuit ensures that the signal isn't floating.

backstreet.devisor said:

In my application, the USB connection needs to be detected. For this purpose I used the schematic from the datasheet of nRF52840DK (schematic in the previous post). But apparently it does not work....

This circuit isn't needed for detecting a USB connection in the application. The USB device controller API have events for USB connected  and disconnected.

I recommend you checkout the USB samples in zephyr for examples on how to use these events:

https://github.com/nrfconnect/sdk-zephyr/tree/main/samples/subsys/usb

 

Best regards,
Bendik

[backstreet.devisor]

Hi. Thank you very much for the explanation.

I will try to implement USB detection following your examples.