GTA04 USB OVP, USB charger detect, USB-OTG & 6400, earjack DL_GSM, JTAG
joerg at openmoko.org
Mon Apr 28 12:34:19 CEST 2008
Andy Green schrieb:
> | o- I suggest PTC-fuse&crowbar USB OVP like attached sketch. Component
> | and exact types to be decided upon by Allen/hw team - just suggestion
> in my
> | sketch.
> I don't know that we really need this protection, or it is a reaction to
> the unknown "switch burnings" that are seen. If it is a goal to survive
> large overvoltage events for long periods on USB, this circuit will be
> good, maybe it will help also with the switch burnings, but is it a goal?
Well it's just a consideration of mine about AbsMaxRating of our device,
that I would like to see to be more robust. A connector that's desgned
for receiving nominal 5V, and goes up in smoke at ~6V, is broken by
design in my opinion, so that's my suggestion to fix a "bug" in hw.
> | o- detect USB charger: should we try to detect D+/D- short? Can we detect
> | 47kR-ID-Pin with 6400 or do we need additional hw to handle this?
> This short is meant to be seen by the "USB OTG" PHY I believe... if 6400
> supports it I didn't look yet.
> | o- what do we need additional hw for 6400 USB-OTG (charge pump, OVP,
> | ESD-prot...)?
> Now we chose pcf50633 we either need some OTG-specific management chip
> that does this, or to re-use the GTA02 parts.
Well for the charge pump (plus possibly additional circuitry) I had a
long visit at 6400-UM, USB-OTG chapter, and at
http://www.usb.org/developers/docs/USB_OTG_1-3.pdf especially 5.1.3, 5.3.4.
It seems there are quite a few very specific requirements for the Vbus
voltage, current, impedance etc pp.
Though 6400 shuld do a lot of the weird signaling of OTG by itself
(that's what I *think*, didn't find decent data on it) there isn't a pin
called USB-OTG_capacitor or sth like that. And Vusb has to be created by
some external component that's not quite clear for it's specs.
I really like to see some application notes on USB-OTG with 6400 from
Samsung!!! Someone who may ask them whether they got soemthing useful?
BTW: this whole USB-OTG pretty much collides with our "externally
powered hostmode", and I really like to use dedicated powerconnector and
use the second power rail of 50633 to have this sorted out. More on this
in a separate mail later on.
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