On Wed, Feb 20, 2008 at 02:46:32PM +0800, Andy Green wrote: > uboot-pcf50633-default-curr-lim-1A.patch > > From: Andy Green <[EMAIL PROTECTED]> > > 1) Stop PMU killing us if we don't have a battery in (by setting > default > current limit to 1A)
On Wed, Wed 20, 2008 at 05:27:28PM +0300, Harald Welte wrote: > This has to have a BIG FAT warning and it needs to be absolutely sure > that this code is _never_ put onto any production / 'sold' devices. You > cannot draw more than 100mA from USB without being configured by the > host. Even in the latter case, you can only draw up to 500mA, since > this is the maximum current requirement that your config descriptor can > indicate. Gentlemen, I would like to echo what I wrote a month ago at <http://bugzilla.openmoko.org/cgi-bin/bugzilla/show_bug.cgi?id=956> and point out that the USB Battery Charging specification <http://www.usb.org/developers/devclass_docs/batt_charging_1_0.zip> allows devices to draw up to 1.5 amperes from a special charger. Special chargers identify themselves by shorting the data lines. If the data lines aren't shorted, then you are limited to 100 or 500 mA, as Mr. Welte notes. I hope that the OpenMoko wall charger will actually short the data lines; I do not understand why the bug report mentions some 48k resistor. By the way, this is my first post on the list. (I hope it won't reject email from non-subscribers; I cc'd you in case it will.) I don't have any experience in implementing any USB stuff so far, but I happen to be interested in mobile charging of mobile devices. Read on if you're interested. I've been thinking about getting myself a mobile phone that could double as a bicycle navigator. Because GPS navigation is quite power hungry, I designed a simple charger for hub dynamos that I will hopefully build within the coming weeks, as soon as I get the circuit board done. Based on my understanding of the USB battery charging specification, the "special charger" section of Nokia_2-mm_DC_Charging_Interface_Specification_v1_2_en.pdf (available from nokia.com) and on my measurements of some old phones of the Nokia DCT-3 series (3.5mm charging connector), I believe that a current-limited 5.0-volt power supply at 500+ mA will work for all three classes of devices. For a dynamo hub, a simple low-dropout rectifier linear regulator ought to yield 80%+ efficiency if the current drawn by the device matches the current supplied by the dynamo. The dynamo is an AC generator, essentially a constant current source; the voltage varies according to load. The nominal output current of the SON28 that I have in my bike <http://www.nabendynamo.de> is 580 mA. If the current limit in the device is set higher than that, the voltage should drop a little from 5 volts and the charge controller should automatically tune down the current. Best regards, Marko Makela http://www.iki.fi/~msmakela/
