Quote:
Originally Posted by Stitchawl
Now this is more like it! (I don't understand it, but at least I can see it's addressing the point of the question!  ) If the purpose of the 'negotiation' is to specify the power requirements, and both chargers are putting out 5.2V with the same polarity, I wonder what could be missing from the negotiation to cause the non-acceptance of the charge? 
Stitchawl |
The current - the USB voltage is specifed to be 5.0V (which is near enough to 5.2V) but it's the amount of current that varies. I think they adhere to the letter of the specs, whereas most devices may not - I'm not 100% about that, but this is the only reason I can see that explains why it works with real controllers what would support the USB 'handshaking' but not with PSUs that would just supply power...
See
http://www.usbmadesimple.co.uk/ums_2.htm ("Device Powering") and
http://www.beyondlogic.org/usbnutshe...htm#Electrical , particulalry "Suspend Current", which I wonder might be involved...