Hi,
I am powering the NRF52840 in normal mode by supplying 1.8v to VDD with VDDH and VDD shorted.
In order to use USB the VBUS pin is connected to the USB VBUS line.
However, I noticed that on the circuit configuration web page (https://infocenter.nordicsemi.com/index.jsp?topic=%2Fps_nrf52840%2Fref_circuitry.html&cp=4_0_0_6_2) it has the following statement:
"
- When supplying power from a USB source only, VBUS must be connected to VDDH if USB is to be used.
"
In fact, my board is powered only from a USB source but via my own 1.8v LDO serving both the NRF52840 and the board's other components.
Since VDDH is already shorted to VDD and both are supplied with 1.8v from my LDO, it would not be compatible to also short VDDH to the VBUS line.
I note also that the NRF52840 datasheet states in the USB section that VBUS must be connected in addition to EITHER VDD or VDHH.
Is the above requirement only relevant when powering the NRF52840 in high power mode from the VBUS line? i.e. reminding the designer not to forget that just because VBUS line is connected to the VBUS pin the VDDH must still also be connected to the VBUS line for power?
Otherwise, could you clarify how USB is connected when running NRF52840 in 1.8v normal power mode?
Thanks in advance,
Justin
