nRF52840 & 20V USB Power Delivery?

[tb32]

Does the nRF52840 work with 20V USB Power Delivery? My system runs on 3.3V and there is no other need for 5V on the board. Do I need to include separate DC-DC conversion for this? If so, what current does it need to support?

[Andreas]

Hi,

 

The recommended operating conditions are 1.7V-5.5V, 20V is outside this. You can just power the nRF52840 from the 3.3V rail in your system, the VBUS supply input in the nRF52840 is taken from the 5V bus power from the USB interface you connect it to. If you do not plan on using the USB capabilities of nRF52840 then you do not need this at all. See the reference circuitry:

https://infocenter.nordicsemi.com/topic/ps_nrf52840/ref_circuitry.html?cp=4_0_0_6_2

 

Best regards,

Andreas

[tb32]

Hi Andreas, thanks for the answer. I am planning on using USB. I will be using a USB C connector so I can use USB Power Delivery to charge the system battery quickly. I will only use the USB 2.0 signals from the USB C connector and will not use the Super Speed signals. The Power Delivery capable charger will increase the Vbus voltage to 20V to provide more power, so I can't connect Vbus to the nRF52840. I have a buck converter to convert the Vbus voltage to 3.3V to power the system. Do I need another 20V input to 5V output DC-DC converter to power the USB on the nRF52840? Does the nRF52840 just convert the 5V Vbus to 3.3V for USB anyway? How much current does the USB peripheral take?

[Andreas]

Hi,

 

OK, I understand. Unfortunately the USB peripheral needs the 5V to drive the front-end, so for this you need a 5V regulator as well. You can find some current numbers in the PS: https://infocenter.nordicsemi.com/topic/ps_nrf52840/usbd.html?cp=4_0_0_5_34_13_0#unique_1058430276

nRF52840 is able to generate 1.8-3.6V from 2.5-5.5V (min 0.3V drop, i.e. can not generate more than e.g. 2.2V from 2.5V supply), which might be feasible for your system, but i doubt it due to the battery (assuming that is ~3.3V). The max external load is also 25mA for <4dBm TX and <5mA for >4dBm TX. In any case you can look into it and evaluate, this is illustrated in the PS, reference circuitry config 1: https://infocenter.nordicsemi.com/topic/ps_nrf52840/ref_circuitry.html?cp=4_0_0_6_2_0#concept_hqh_j22_fq

 

Best regards,

Andreas

[tb32]

Could I use Configuration #3 with 3.3V VDD_nRF and 4.35V VBUS at 5mA? I will need more than 25mA elsewhere for 3.3V so would need to keep that powered externally. Thanks.

[Andreas]

Hi,

 

Yes, config 3 illustrates how to supply the nRF52840 in 'normal voltage' operation (VDD_nRF = 1.7V-3.6V). VBUS = 4.35V is on the lower edge of the recommended operation conditions though: https://infocenter.nordicsemi.com/topic/ps_nrf52840/recommended_op_conditions.html?cp=4_0_0_7 

 

Best regards,

Andreas