On Friday 18 April 2008 18:34, Michael Shiloh wrote: > Hi everyone, > > With input from the experts who designed the system, I've tried to > document precisely how charging works on the Neo Freerunner. > > I welcome your feedback: > :)
> > The Neo Freerunner charges the battery when 5VDC is provided at the USB > port, whether from a computer USB port or from a dedicated USB charger. > > The Neo Freerunner can charge most rapidly when it can pull 1 Amp from > the power supply connected to the USB socket. However, not all chargers > or computers can provide this much current. It might seem like a dumb question, the the charger provided can source 1Amp, right? :) > When the Neo Freerunner detects that power has been provided at the USB > port, it will attempt to draw only 100mA. This minimum is mandated by > the USB standard. This amount of current is insufficient to both power > the Neo Freerunner (or even just its backlight) and to charge the > battery, and therefore the battery will not be charged. (The battery > discharge rate, however, will be slightly lower, as the supplied 100mA > will be used to augment the battery.) > > (When a charger is connected to the USB port, the Neo Freerunner > automatically powers up. Thus, if charging at 100mA is desired, the Neo > Freerunner must be shut down after the startup process has completed.) On the GTA01 you can press AUX as you power up to get the boot menu. On mine I have added an option to start fast (500ma) charging and power off the backlight. This means I don't need to have enough power to do a full boot to get the device charging. Perhaps an option for slow (100ma) charging that turns the backlight off would be useful - although it would probably need to have a few tests run to see if it was actually helping any. > After detecting USB power, The Neo Freerunner will attempt to negotiate, > via the USB protocol, a higher charge rate of 500mA. If the device > powering the Neo is capable of doing so, the Neo Freerunner will charge > at 500mA. > > USB chargers do not implement the USB protocol, and thus can not respond > to requests for higher charge rates. Some manufacturers have worked > around this issue by installing resistors of different values between > different pairs of pins in in order to "identify" their own chargers of > known capacity. This is not part of the USB standard and is completely > up to each manufacturer. I presume that if I accidentally plug in <insert device that charges via usb here> it would simply charge at 100ma? > > The USB charger provided with the Neo Freerunner can source up to 1A. In > order to identify this special charger, there is a 47K ohm resistor > between the ID pin and ground. If the Neo Freerunner detects this > resistor, then the Neo Freerunner will charge at 1A. > In summary, the Neo can charge at 3 different rates: 100mA, 500mA, and 1A. Do you have any information on how long each takes to fully charge the battery (excepting of course the 100ma option unless the stuff I mentioned above works)? > Notes: > > 1. USB negotiation and resistor detection is performed in software, and > is thus under developer control. A developer might write an application > to indicate that 500mA or 1 Amp are available, bypassing the USB > negotiation and the 47K ohm resistor detection. I assume OM don't want to go anywhere near the software that overrides this for legal reasons and that it'll always be something a user has to deliberately add themselves? > There is nothing preventing the software from charging at a higher rate > than then power provider can supply, although there is danger in doing so. > > The danger in drawing more current than a charger or computer USB port > can provide is that components overheat and may become permanently > damaged, or even catch fire, although most USB host devices implement > current limits that will depower the port on overcurrent. > > 2. The Neo Freerunner charger is a single assembly which includes > the USB cable. The cable is NOT a separate item and can not be removed > from the charger (without cutting). > > 3. Any third-party charger that does not contain the 47K resistor will > cause the software to assume it can draw only 100mA, regardless of how > much current the charger really can source. > 4. In its hard-coded configuration, the PMU doesn't charge the battery > at all. The hard-coded configuration is used when power is applied to > the PMU after a period of complete absence of power, including the > backup battery. How long is this period are we talking weeks,months or years? > When the system comes up, it reconfigures the PMU to enable charging. > Most of the configurable items are also preserved by the PMU if it > powers the system down, but the PMU itself still has power - either from > USB, main battery, or the backup battery. (This is the PMU's STANDBY mode.) > > 5. All of this discussion is for setting the maximum current that the > Neo Freerunner can safely draw from the USB socket. The battery charging > current may actually be lower, if the charging logic determines that a > lower charge rate is appropriate. > Can the Freerunner operate at all without a battery - ie solely from a usb (pc or plug in the wall) charger? -- Andy / ScaredyCat _______________________________________________ Openmoko community mailing list community@lists.openmoko.org http://lists.openmoko.org/mailman/listinfo/community