Nrf52840 USB Power Configuration from Nordic Infocenter Misleading?

[CBSwift]

Hello!

I'm in the process of prototyping a PCBA that is Battery Powered  with VDDH (Tied to VDD for now), but also has the option of USB Power.

When USB Power is active, Batteries are Shut-down with a Mosfet.

I DID Notice that I must have VBUS connected to VDDH for the unit to power on, per Nordic's guidance I have seen in the DEVZONE.

This is OKAY- however I have two points that are confusing and could use clarification.

1. We are using a Module with the nrf52840 Chipset. DECUSB is inaccessible. I assume there is a decoupling cap On-board the module as there is access to VBUS, but this is still unknown. What are your thoughts on this?

2. Why does the official Nordic nRF52840 Circuit Configuration(Shown below, taken from Nordic Infocenter) NOT tie VBUS->VDDH?... yet guidance is that shorting VBUS->VDDH is necessary? It's confusing. Could you clarify? Again, I know in our mode we do need VDDH shorted to VBUS for USB operation, but the official Nordic Config is confusing (see picture below). I would like to have the most simple power config possible.

Thanks! Been working with this chipset for two years now and we love it.

Sincerely,

Colin

[Bendik Heiskel]

Hi Colin,

1. We are using a Module with the nrf52840 Chipset. DECUSB is inaccessible. I assume there is a decoupling cap On-board the module as there is access to VBUS, but this is still unknown. What are your thoughts on this?

If VBUS and the other USB connections, D+ and D-, is accessible on the module it would be save to assume that the decoupling capacitor on DECUSB is populated seeing as it is needed for using the USB interface. If the module datasheet does not mention whether this capacitor is present, you would have to contact the module manufacturer to be completely sure.

2. Why does the official Nordic nRF52840 Circuit Configuration(Shown below, taken from Nordic Infocenter) NOT tie VBUS->VDDH?... yet guidance is that shorting VBUS->VDDH is necessary? It's confusing. Could you clarify? Again, I know in our mode we do need VDDH shorted to VBUS for USB operation, but the official Nordic Config is confusing (see picture below). I would like to have the most simple power config possible.

Circuit configuration no.1 show the power configuration for using VBUS for powering the device, here VBUS is connected to VDDH. The other configurations either use normal voltage mode, VDDH shorted to VDD, or are configured for using a external regulator or battery in high voltage mode.  Config 1 are configured for using the LDO for both regulator stages, if you plan on using the DC-DC converters you can just add the required components from the other configurations.

 

Best regards,

Bendik