Author Topic: Inrush current with BC1.2  (Read 34 times)

jsjohnsen

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Inrush current with BC1.2
« on: July 10, 2019, 01:00:46 am »
Must a device meet the inrush current requirements on a CDP and DCP port?

In example:
I have a device that detects that it is connected to a CDP port.
The charging with 500mA is initiated 30ms after the device connects to VBUS.
If I do an inrush current test in this scenario it is a fail, but I am not using more power than CDP allows.
(my device meet the inrush requirements on an SDP port. I charge 2.2uF capacitor, and current consumption is keept below 100mA)

In the BC1.2 inrush current is only mentioned in dead battery provision (section 2.2)
In this case a device connects to a SDP port, and in my point of view must follow the rules set by USB 2.0
The latest update of the "inrush current test description" from USB-IF is from 2008 and do only mention USB 2.0, and nothing about CDP/DCP.

Best Regards
Jesper Johnsen

Jan Axelson

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Re: Inrush current with BC1.2
« Reply #1 on: July 10, 2019, 03:06:19 pm »
The reason for the inrush current requirement is that a too large current can cause the VBUS voltage on adjacent ports to drop, causing attached devices to disconnect.

A CDP is required to be able to provide 1.5 A at any time.

If your device draws less than 1.5A, I don't see a problem. I'm not aware of any compliance test that would cause an issue for you on this.