[nRF52820] USB Power Configuration

[sunghoryu]

Hello!

I'm hoping to use the nRF52820 (QFN package) powered by a USB connection (not with external battery).

I'm referring to Figure 153 of the datasheet, which shows Circuit Configuration #1 and is the only reference design available showing a USB-powered connection:

From the notes above in Section 7.3 Reference Circuitry, it seems that when supplying power through USB, VBUS and VDDH must be connected:

My questions are:

(1) When powering the nRF52820 using USB, it is only possible to use High Voltage mode (Normal Voltage mode is not possible), correct?  As shown in Section 5.3.1 Main Supply?

(2) In High Voltage mode, since VDD is internally generated, would this be the voltage rail that SPI and other logic signals pull-up to?

(3) Similarly, when using an external J-Link to flash the nRF52820, the power pin of the J-Link would connect to the internally generated VDD rail?

(4) Would a configuration like this be possible where VDD and VDDH are connected and supplied externally, while only VBUS is connected to +5V?  If not, why not?  FYI, the diagram below uses nRF52840 but the idea would be the same for nRF52820

Thank you!

[JONATHAN LL]

'm referring to Figure 153 of the datasheet, which shows Circuit Configuration #1 and is the only reference design available showing a USB-powered connection:

You can add DCDC components if you want, so we dont show all possible combinations, but for the USB section this is correct. 

From the notes above in Section 7.3 Reference Circuitry, it seems that when supplying power through USB, VBUS and VDDH must be connected:

Correct, VDDH needs to be used here. The alterative here is to have a external regulator that steps down the voltage that you could then use to supply the device in normal voltage mode. So something like the figure 2 https://docs.nordicsemi.com/bundle/ps_nrf52820/page/ref_circuitry.html#ariaid-title3 is also an option. 

(1) When powering the nRF52820 using USB, it is only possible to use High Voltage mode (Normal Voltage mode is not possible), correct?  As shown in Section 5.3.1 Main Supply?

It is not possible to power the nRF52 in normal voltage mode directly from the USB as the voltage is to high. https://docs.nordicsemi.com/bundle/ps_nrf52820/page/abs_max_ratings.html 
 

(3) Similarly, when using an external J-Link to flash the nRF52820, the power pin of the J-Link would connect to the internally generated VDD rail?

Correct. 

(4) Would a configuration like this be possible where VDD and VDDH are connected and supplied externally, while only VBUS is connected to +5V?  If not, why not?  FYI, the diagram below uses nRF52840 but the idea would be the same for nRF52820

You can use an external regulator to step down the voltage so that the nRF can work in normal voltage mode. 

Regards,
Jonathan

[sunghoryu]

Hello Jonathan,

Thank you for the prompt response!  Some follow-up questions:

(1) So Figure 2 shows VDDH being connected to VDD instead of VBUS. Would this be the Normal Voltage mode? Assuming VBUS is connected to +5V of the USB, would VDD_nRF be externally supplied i.e. +3V3 buck converter? Would this be a safe mode of operation for the nRF52820?

(2) I was under the impression that USB operation and Normal Voltage mode are mutually exclusive. That would not be the case?

(3) When using USB as the main voltage source, is there an advantage/disadvantage to using High Voltage mode over Normal Voltage mode?

(4) I would like to request a quick schematic review for the nRF52820, just to make sure all the wiring and power sequence is correct.  Would you be able to share an email of point-of-contact?

Thank you!