Enabling USB communication

[Dan Colob]

To be able to have USB communication/interface, do I need to apply 5V to VBUS? Or will 3V on Vdd be enough. I am planning to use coin cell that is max rated for 4.2V so it won't be able to provide 5V. 

[awneil]

Dan Colob said:

I am planning to use coin cell that is max rated for 4.2V so it won't be able to provide 5V

But the USB itself will provide 5V - surely?

Dan Colob said:

do I need to apply 5V to VBUS?

Have you read the USB section in the Product Specification?

https://infocenter.nordicsemi.com/topic/ps_nrf52840/usbd.html?cp=4_0_0_5_34

eg,

"The signal pins and the pull-up will operate only while VBUS is in its valid voltage range"

"The physical layer interface (PHY)/USB transceiver is powered separately from the rest of the device (VBUS pin)"

"Enable USBD after VBUS has been detected only"

etc, ...

[Dan Colob]

Yes I have read the USV section, just wanted to make sure, thanks . The nRF will be used in portable device so won't have a USB cable connected so will need to have the coin cell supply.

1. Any documentation/resources you have for using a boost converter with the nRF?

2. How much power does the 5V take?

Thanks

[awneil]

If it doesn't have a USB cable connected, there's no point in enabling the USB - is there?!

And when there is a USB cable connected - it gives you the 5V !

[Dan Colob]

For our application there is a point since one of our signals outputs using USB interface/protocol for communication which will feed into the BLE and then transmit

[awneil]

But if you have a USB connection, that must provide the 5V - that is part of the definition of USB!

[Dan Colob]

No, I am going to have a transmission line going into the USB interface of the nrf. No USB connector is connected where I will plug in the cable to something like a laptop to get 5V because this is a PORTABLE device

[Dan Colob]

Anyway, I do not want to continue that discussion with you, if you could help me with question 2: How much power does the 5V take?