[PATCH 1/1] uboot-pcf50633-default-curr-lim-1A.patch

Andy Green andy at openmoko.com
Fri Feb 22 13:16:09 CET 2008

Hash: SHA1

Somebody in the thread at some point said:
> 2008/2/22, Andy Green <andy at openmoko.com <mailto:andy at openmoko.com>>:
>     Well it is interesting but the charger thing is a done deal for us
>     already and it is okay as far as it goes.  It would have been nicer to
>     use this standard method, but if as Harald says if it turned up too late
>     to use it, well its okay.
> I understand. The specification is less than a year old, and it takes
> time until it is implemented in widely used chipsets.
> However, I hope you can consider adding a user-space interface for
> specifying the charging current. Then I could violate the USB
> specification and build a device that would charge the OpenMoko while it
> is in USB host mode. The device would provide a USB HID interface to
> some sensors, such as odometer (about 85 mm steps from the dynamo hub),
> cadence, and heart rate. Then the OpenMoko would record all this
> information during the bicycle trip.

No, no problem there you just need to add a resistor to the USB cable
you use to hook to the dynamo to tell it you are the 1A charger.  Better
that the charging mode is tied pretty firmly to its understanding of
what it is hooked up to (a plan that will only get more "right" when we
extend it to this "play dead if no 500mA USB descriptor accepted yet" mode).

> Failing that, I think I can afford to wait a couple of more years for

Gah not at all, you can patch the kernel sources if you want it :-)  You
can get what you want right away like that even if it was only for
yourself.  I just think the resistor method is best, since the PMU max
charging current is 1A anyway.

> Right. The overvoltage protection consists of two 5-watt zener diodes
> before the MOSFET rectifier bridge, and a low-dropout 5-volt regulator
> after the rectification. I hope it will be sufficient, but I'll have to
> test it to be sure. This protection will be needed when there is too
> little or no load when the circuit is connected to the dynamo. For
> instance, old (3.5mm) Nokia phones tend to interrupt the charging
> current at about 2 Hz rate. Without any load after AC/DC rectification
> (testing with a salvaged wall-wart), I measured up to 96 volts from the
> output capacitor. :-)

Lovely... you can get some very strong automotive switch mode regulators
that can survive this kind of crap, you should have a google around.
They are built to take a variety of insults found in automotive power
like the starter motor starting and stopping, and would make a great fit
for this kind of power source.

- -Andy
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