VBUS supply before system ON on normal voltage mode nRF52833

[deep_dive]

1. Our system is configured with circuit config3 of the nRF52833 WLCSP, where an external power supply of 1.8V is applied to VDD.

Power sequence : USB connection -> VBUS supply -> external LDO 1.8V output -> nRF52833 VDD supply 

Due to the turn-on time delay of the external LDO, the V_USB pin (for VBUS & USB Type-C detection) is supplied before the VDD 1.8V of the nRF52833.

Is it OKAY?

In other words, is it okay for V_USB at 5V to be supplied before VDD at 1.8V in a system configured for normal voltage at 1.8V?

2. According to the datasheet section 5.3.2,when the system is OFF and VUSB is applied, the system turns ON.

Does this mean that the system will turn ON regardless of whether the system circuit configuration is in high voltage mode or normal voltage mode?

3. If the system turns ON when VBUS is connected while in normal voltage mode and the system is off, I thought this is because the VUSB LDO is working.

Are the VUSB internal LDO and the VDD internal LDO different from each other?

[Simonr]

Hi

Happy new year, and sorry about the late reply. We have asked for some help from some experts internally on question 1 here to make sure, but I think it should be okay. Please wait for confirmation though.

2. When the device is in system OFF, and VBUS trigs a reset because it reaches a valid range, the device resets and thus will run the startup as when you first start up the device, in whichever is set by default (VDD/VDDH).

Best regards,

Simon

[deep_dive]

thank you simonr

About #2 question, 

You mean that when VBUS trigs, the devices can power up by VBUS whatever the power configuration(VDD/VDDH) is. Right?