I have a Sony Xperia phone. I have 2 USB-to-USB-micro cables, a power charge-only one and a data/charge one.

I connect the phone to my PC to charge the phone. When the PC is on, both cables charge the phone. So far so good.

When the PC goes to Sleep mode:

  • the charge-only one still charges the phone
  • the data/charge cable no longer charges the phone

Why on earth should this happen?

  • \$\begingroup\$ Does the charge-only one charge the phone slower than the data cable? \$\endgroup\$ – Brian Drummond Feb 25 '13 at 13:04
  • \$\begingroup\$ Hmm, it's slow but I am not sure it is slower... \$\endgroup\$ – Bill Kotsias Feb 25 '13 at 13:05
  • 1
    \$\begingroup\$ Such questions are off-topic - nothing to do with electronic design! \$\endgroup\$ – Leon Heller Feb 25 '13 at 13:10
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    \$\begingroup\$ Actually Leon, it does - specifically, an often overlooked part of the USB spec. \$\endgroup\$ – Chris Stratton Feb 25 '13 at 15:22
  • \$\begingroup\$ No electronic design is involved. \$\endgroup\$ – Leon Heller Feb 25 '13 at 16:05

USB has sleep/suspend mode options. Conceivably, the phone has received the suspend signal over the data pair, and stops charging. This is very much dependent on the phone, the computer's hardware design, and the computer's OS though, so it is just conjecture. USB Suspend specification requires a maximum of 500µA, some of which is taken by the pull-up/pull-down resistors that are part of the USB spec.

Easy enough to test though, get a second regular (data+charging) cable, and try it with that. If it also stops charging when the computer goes to sleep, then it's normal. If it doesn't, it would be an issue with the first cable.

As for why the power only cable still works, your computer has standby power on USB, the data lines are not connected, so the phone believe it is on a regular usb charger (it has no way to tell the difference). If the power is there, the phone will take it.

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