NRF52840 / Power-up sequence needed?

[Mickael]

Hi there,

Is there a specific sequence needed to power-up the NRF52840?

Let me get into the details:

• My design uses configuration #5 from the datasheet (see below)
• Due to my power tree,  in certain conditions (e.g. no battery connected or battery dead), when plugging USB, VBUS will appear up to on the pins of the NRF52840 ~5ms before VDD_nRF actually ramps up. 
• Is this a potential issue for the chip? 
• I have monitored DCC and DEV3V3 outputs in the period where only VBUS is ON and havent spotted anything specific but I thiought this worth checking with you anyway to see if you see any risks 

Thanks for your help,

Mickael

[ketiljo]

Hi Michael

I have checked with the design that made the VBUS regulator: "Nothing bad should happen. The chip will not be damaged in any way, and is kept in a defined state until VDD_nRF has ramped up and power-on reset de-asserted."

best regards,

Ketil Aas-Johansen