USB Battery Charging without Microprocessors

Whoops, answered my own question (and the answer is yes, I can do it all analogly).

Yes. They have to negotiate power levels.

"Hi, I'm a USB device and I need 500 mA".

"Sorry, I only have 100mA."

There's always a way. Whether it's a *good* way depends.

in usb2 the max is 900mA, for dedicated chargers i believe it is +1.5A

it depends on whether you connect to a computer, a charger or a computer that can act as a charger

as Tim found there's a spec for it

-Lasse

No micro required. I think the requested current can also be set by some resistors but obviously you will need a circuit to properly and safely charge the Li battery. See Minty Boost at: "

The meat you are interested in is here: "

The max current specs have obviously changed over time.

I have a old Core-2-Duo Mini ITX MB here that will Halt and show an error in text on the screen if too much current in drawn from the USB bus. It's a pretty nasty handling of an over current condition.

Cheers

On the plus side, the thing probably cost a whole dime less than it would have if the mobo were protected from excess USB current draw.

It's not clear to me if Tim wants to run off a "real" USB port, off a USB- charger type of device, or both.

In the case of a "real" USB port, it'll certainly have to be negotiated.

OTOH, that doesn't work at all for most USB chargers, which don't have nearly the brains needed to support that. There are several schemes in use, all doing odd things to the D+ and/or D- lines (sinking one or the other to Vs or ground via a resistor, that sort of thing) to indicate that they support more than the standard minimum (100ma).

So determining the maximum available power on the port requires checking for the (several) schemes fiddling with D+/D-, failing that negotiating with a "real" USB host, and failing that assuming 100ma.

Fortunately there are chips that will do at least a partial job of that, but I don't know of one that supports all of the schemes in use (Sony, Apply, DCP, a couple of schemes used in China, several other custom schemes that exist mainly to sell "special" chargers at exorbitant prices) simultaneously.

And if it's not, there's no general statement to be made, SFAIK. You've constrained the state space nicely.