nRF5340 Hardware Design Questions - VDD, VDDH, VBUS

[FARLY7]

Hi there,

I am currently working on a design using the nRF5340 and nRF21540 FEM. The entire device will be powered over USB VBUS. For my design, I am following the reference design given in "Section 9.3.4 Circuit configuration no. 4 for QKAA aQFN94" (Config 4) of the nRF5340 Product Specification v1.3.

"Section 4.5.2 High Voltage mode" notes that when powering the device with VDDH and VBUS, the VDD regulator can be used to power external components.

I have a few questions:

1. Is the VDD regulator capable of powering the nRF21540? I don't think it is, as the nRF21540 has a peak current consumption of 110mA, and the only value I can find regarding the nRF5340's VDD line is an output between 1-7mA ("4.7.5.2 Regulator specifications, VREGH stage"). This seems very low, so I just want to check in case I am missing something.
   
   1. If I need to instead add an additional 3.3V external regulator to power the nRF21540, is it better to power the nRF5340 from the same external regulator, or just keep it connected to VBUS?
2. Are the decoupling capacitors on the VDD line required when the VDD is in output mode? I assume so, as they are shown in the reference design. However, I would just like to check, as I thought decoupling capacitors would only be required when the VDD is used as an input.
   
   1. Are decoupling capacitors required on the VDD pins where nothing is connected?
3. As VDD is in output mode, is it still required to tie all of the VDD pins together? I assume so, as it is shown in the reference design, however I just want to check. I guess this is to spread the load across multiple pins or something?

Thanks,

Sean

[JONATHAN LL]

Hi Sean,

Is the VDD regulator capable of powering the nRF21540?

No. 

If I need to instead add an additional 3.3V external regulator to power the nRF21540, is it better to power the nRF5340 from the same external regulator, or just keep it connected to VBUS?

It depends on your use case, so there is no real correct answer here. But using a single regulator to supply both the nRF5340 and the nRF21540 will be less complex and likely cheaper then having two regulators on board. 

We do also provide PMIC's so you could look in to that if you want.  https://infocenter.nordicsemi.com/topic/struct_pmic/struct/pmic.html?cp=7 

Are the decoupling capacitors on the VDD line required when the VDD is in output mode?

Yes they are still required. 

Are decoupling capacitors required on the VDD pins where nothing is connected?

all (relevant)components shown in the ref. circuit should be added. 

As VDD is in output mode, is it still required to tie all of the VDD pins together?

yes. 


You can see more info on how the regulators work in these sections: 
https://infocenter.nordicsemi.com/topic/ps_nrf5340/regulators.html?cp=4_0_0_3_6 
https://infocenter.nordicsemi.com/topic/ps_nrf5340/chapters/usbregulator/doc/usbregulator.html?cp=4_0_0_3_7 


Regards,
Jonathan