RE: USB Charge Source Detection w/ nRF52840

Stian Røed Hafskjold — Mon, 13 Aug 2018 11:23:03 GMT

Answer from HW engineers:

The USBD is USB 2.0 compliant, but does not have built-in support for the Battery Charging Specification rev 1.1. This implies that if it's connected to a Charging Downstream Port (CDP) or a Dedicated Charging Port (DCP), it will not recognize them as such. It might be possible to implement power source detection under software control, but this is not tested.

It could be possible to use the USBRESET event to decide whether the device is connected to dumb charger or not. When connected to a SDP or CDP, a USBRESET event should be generated within a certain time after USBPULLUP is enabled. But when connected to a dumb charger (DCP), it is not possible to have the USBRESET event, since it requires both D+ and D- to be pulled low for a specified amount of time. The dumb charger does not have any pull-down resistors on the data lines, and with the pull-up resistor on D+ enabled from the nRF52840 side, it is not possible for D+ to go low. (I believe there are some dumb chargers that do not have D+ and D- shorted together. In that case D- will float, but the reset state still cannot occur because D+ is pulled high by the resistor.)

RE: USB Charge Source Detection w/ nRF52840

Stian Røed Hafskjold — Tue, 17 Jul 2018 09:02:06 GMT

Hi, I forwarded this question to the HW designers. I will come back with an answer later.