Power rail for nrf 5340

[Barsa]

I am working on a wearable which has Fanstel BT40F MCU (SOC nrf 5340). when i initially turn on my pmic, it can only generate 1.8 volt from buck 1 regulator and I am thinking of using vdd pin for this 1.8 v and flash my firmware, but once the firmware is flashed i need 3.3 volt in MCU as some of my peripheral require more than 1.8 volts. So I have configured my PMIC to generate 3.3 volts from LDO2 regulator of PMIC once the firmware flashes. But my problem is how do I handle two power sources in my MCU efficiently? I was thinking of using vdd pin for 1.8 volt and vddh pin for 3.3 volts, but when I looked at the schematics of nrf 5340, vdd and vddh should be tied together to use vdd pin as a power source and vddh should be isolated if I plan to use vddh as power source, I am not sure how could I handle these two power sources in my schematics for nrf 5340. 

[Simonr]

Hi

Wouldn't this be what the PMIC would do in your circuit? The nRF5340 won't be able to switch power sources seamlessly during runtime, but switching between VDD and VDDH with a reset/power cycle between, as it can be run on either VDDH or VDD when configured for VDDH, as that won't disable/exclude the VDD option

But to make this change during run time I think you need the PMIC to make the voltage change during runtime. Also, the regular VDD is able to run both 3.3V and 1.8V, so VDDH might not be necessary in this case.

Best regards,

Simon