3 ms·

You say cost optimization, I say safety feature.

• dTal 8y ago
  That "safety feature" prevents the client device from negotiating a higher current limit than 100mA. The host controller may generously provide more, but there's no guarantee of this without the data lines.
  • londons_explore 8y ago
    The host is required to not be damaged by a short circuit on the power lines. That means a device can ignore the signalling entirely and just keep taking more power till the supply turns off, and then scale back 10 percent. More and more Android phones do that, and it works very well. Only disadvantage is if you plug it into a hub, it can cause the whole hub to go out for a bit. Devices solve that by not using the above algorithm when they detect any active signalling.