Looking for advice on the proper DCCH pin connection nrf52840

[Kaihi]

[ Just figured out it doesn't work the way I thought ]

Hi,

Right now I'm looking down at the nrf52840 datasheet, because I would like to do a project with such MCU, but I got to the part of the integrated DCDC converters and I have a doubt.

At the moment I'm thinking in feed the MCU with an external 3.3V LDO, but in the datasheet there is a schematic that displays we need to wire DCCH pin to VDD pin through an inductor, but in the schematic VDD is outputing voltage VEXT. Can I just connect the DCCH pin to the external LDO's output with an inductor? or...

The project is going to use both battery and sometimes USB, for that approach I'd like to use the BQ25622E, it has a powerpath, do you think it is more efficient to connect directly such powerpath to VCCH or keep the LDO TPS7A02(it has a very low quiescent current 20nA on stand by) to feed VDD pin.?

Will the internal LDO be more efficient than the TPS7A02?

click the image to get a full view

Is the example on the right of the image possible?

Hope your answers 

[Hung Bui]

Hi Kaihi, 

I saw your note. Please clarify if you still have question ? 

Please be noted that VEXT is the power from the chip to supply to external peripheral outside of the chip. 
Also it's quite confusing that you mentioned about DCCH but in the figure the change you made was with VDDH.

[Kaihi]

Hey Hung Bui, thanks for your response,

Yeah I was confuse about DCCH, now after reading posts and chatting with IA I figured out that the example on the right doesn't makes sense, but just for curiosity what would happen if I acutally do the example on the right, the REG0 will be bypassed because VDD is shorted to VDDH, right? so the inductor would be ignored or it will atually hurt the nordic?

I have another question when we use the DCDC on REG0, the voltage generated flows from DCCH pin to VEXT net and goes in to VDD pin, or from VDD to VEXT net and goes into DCCH?

[Hung Bui]

Hi Kaihi, 

Kaihi said:

just for curiosity what would happen if I acutally do the example on the right, the REG0 will be bypassed because VDD is shorted to VDDH, right? so the inductor would be ignored or it will atually hurt the nordic?

I assume you supply the chip in Normal mode (3V), not high voltage mode, correct ? 
Then it's fine the REG0 will not be used and doesn't matter if you have the inductor or not. 

Kaihi said:

I have another question when we use the DCDC on REG0, the voltage generated flows from DCCH pin to VEXT net and goes in to VDD pin, or from VDD to VEXT net and goes into DCCH?

I would suggest to take a look at figure 4 here: https://docs.nordicsemi.com/bundle/ps_nrf52840/page/power.html#ariaid-title6

DCCH is used to connect the LC inductor to DCDC. So the flow of current is from VDD to VEXT. DCCH pin works as a part of the DCDC (REG0) to supply the current to VDD.