nRF5340 - How to enable High Voltage mode

[Gabriele]

Hi,

I've developed a custom board with nRF5340-QKAA (see schematic sheet attached).
nRF5340's VDD pins are not tied to VDDH pin, then I assume the nRF5340 automatically starts in High Voltage mode.
In my design I use

VDD_HV = 5.00 V

When the board is powered up I get

VDD_nRF = 1.77 V

Q1: Is this value compatible with the High Voltage mode operation ?
Q2: How to increase VDD_nRF to 3.3 V ? Is there some special configuration switch in Zephyr ?

Thanks

[ketiljo]

This is normal and correct. When you use VREGH, it will start with the lowest voltage, 1.8 V. You have to configure the voltage by writing to the UICR: https://infocenter.nordicsemi.com/topic/ps_nrf5340/chapters/uicr/doc/uicr.html#register.VREGHVOUT

[Gabriele]

I'm experimenting with the sample application ncs/nrf/samples/Bluetooth/peripheral_uart.
Do you know how to change VREGHVOUT register's content from application main ?

[ketiljo]

Just write to the register. It's like any other register you can write directly to. But note that you have to do a reset for the change to be applied. The VREGOUT register is only read after a reset.

[Gabriele]

I've used nrfjprog

$ nrfjprog -f nrf53 –memwr 0x00FF8010 –val 5

Q1: how to do that programmatically ?

This is what I've found on three different boards
 
UICR.VREGHVOUT = 7h (VDD 1.8V)
Meas #1: 1.77 V
Meas #2: 1.74 V
Meas #3: 1.77 V

UICR.VREGHVOUT = 5h (VDD 3.3V)
Meas #1: 3.23 V
Meas #2: 3.15 V
Meas #3: 3.22 V

Truth be told, there is some board-to-board variability.

Q2: Are these values within the normal operating range ?

Thanks

[ketiljo]

This well within spec. at +/-5%