How do I get the nRF52840 to enumerate as a "bus powered" USB device, to then be allowed to draw 500mA from a PC's USB port.

[Nicholas Lee]

I have a nRF52840 based product prototype which includes a power management integrated chip (PMIC) and a Li-Po battery.

The product recharges via a USB connector. The USB data lines from this connector are connected to both the PMIC and the nRF52840.

If the product is plugged into a dedicated USB charger, the PMIC will detect the short-circuit between the USB data lines and will start fast-charging the LiPo battery at 500mA.

If the product is plugged into a PC's USB port, the PMIC will detect this and will default to start charging the Li-Po battery at 100mA.

However, this 100mA charge rate should then be overridden (to 500mA) by a command from the nRF52840 to the PMIC if the nRF52840 does USB enumeration with the PC and successfully negotiates with the PC that the nRF52840 is a "bus powered" device that needs 500mA.

My question is how exactly do I go about programming the nRF52840 to USB-enumerate with a PC, and then negotiate this "bus powered" status.
Thank you.

[Kenneth]

Hi,

The control endpoint descriptor can be setup to request 500 mA (bMaxPower, also check SelfPowered field). If the host is not able to provide this, it will refuse enumeration.

You can read out the current state by calling app_usbd_core_state_get() (=the state "CONFIGURED" indicates that you're done enumerating):
https://infocenter.nordicsemi.com/topic/sdk_nrf5_v16.0.0/group__app__usbd__core.html#ga14724c533a0374e73338f7618a116cf4 

In general:

- If the USB HOST sets the device into suspend, you're limited to 2.5 mA.
- If the USB HOST does not set you into suspend, you're limited to whatever is set in bMaxPower
- If you connect to a USB host with only VBUS and GND, you're limited to 100 mA.

Also check out: http://www.testusb.com/power_issue.htm

Best regards,
Kenneth

[Nicholas Lee]

Thanks, but I feel that this this jumps over several dozen steps.

How do I even get started with using USB on this chip?

What do I need to do to get to the point where I can call that function.
Is the USB enumeration an automatic part of the chip, or do I need to do something to enable it, include libraries, configure particular settings, call initialisation routines, or what?
Please can you walk me through the basic steps required by someone unfamiliar with this chip. Thank you.

[Kenneth]

Hi,

I don't have any other suggestion than to look at the

USB examples: https://infocenter.nordicsemi.com/topic/sdk_nrf5_v16.0.0/examples_usb.html?cp=6_1_4_6_52 

USB library: https://infocenter.nordicsemi.com/index.jsp?topic=%2Fsdk_nrf5_v16.0.0%2Flib_usbd.html

USB driver: https://infocenter.nordicsemi.com/topic/sdk_nrf5_v16.0.0/hardware_driver_usbd.html 

Best regards,
Kenneth