Detecting USB devices at startup?

[Bernd Walter]

On Tue, Nov 06, 2007 at 03:27:57PM +0200, Krassimir Slavchev wrote:
> Bernd Walter wrote:
> > On Tue, Nov 06, 2007 at 12:01:50PM +0200, Krassimir Slavchev wrote:
> >> Yes, It looks like a power issue but the power supply used in the
> >> development board is very good designed (LM2576 is used). I will measure
> >> power line again. Also the PWM frequency might interfere with PLL.
> >> I will try to find powered hub to make tests. All usb hubs on the market
> >> are bus-powered :(
> > 
> > I can ensure you: there are self powered hubs.
> > If in doubt buy a seven port, they can't work bus powered.
> 
> Ok, I will look for bigger hub.

I'm still a bit surprised, since there are so many noname hubs with
fat wallwarts.

> > Is the LM2576 really used for USB?
> 
> http://www.harerod.de/centipad/documents/CentiBOB201psk_color.pdf
> Look at sheet 2.
> 
> > This is a very beefy thing just for a single port and everything else
> > in a AT91RM9200 system is running at 3,3V or lower.
> > On my board I use such a 257x regulator for 3,3V, separate linear
> > regulators from 3,3V to supply the 1.8V for core and switch and
> > another linear regulator directly from input for 5V to USB.
> 
> There is another voltage regulator TPS767D301.
> http://www.harerod.de/centipad/documents/CentiPad_Programmers_Model_205.pdf
> Look at sheet 13.

Interesting, so they run everything linear regulated from 5V.
Sounds like a lot of power loss, but their board is different and
maybe they have more 5V components.
My board only needs 5V for USB, so I never saw the need for efficient
5V and prefered efficient 3,3V, which is also quite loaded from the
switch.

-- 
B.Walter                http://www.bwct.de      http://www.fizon.de
bernd at bwct.de           info at bwct.de            support at fizon.de