Re: [Gumstix-users] USBnet doesn't work with certain daughterboards at 3.8 V power

[Dave H. <dhy...@gm...>]

Hi Andrew,

> I still don't understand why the STUART daughterboard worked while the
> breakout-gs did not.  Unfortunately I didn't have time to do the
> Vbatt/Vbus/Y0_RTS/Y0_CTS measurements for the STUART setup.  I'll try
> to do that tomorrow.

I think I know what's going on.

On the back of the breakout-gs is a ferrite bead called FB2. You can
see it on the schematic here:
<http://pubs.gumstix.com/boards/BREAKOUT-GS/PCB00011-R901/B00011.JACK.png>

If the breakout-gs board is going to be USB powered, then the bead
should be present. If the breakout-gs is going to be powered from the
power jack then the bead should be removed.

As you suggested, the DC/DC converter is going to dominate the VBUS
from USB. Removing FB2 allows them to not fight with each other.

Early breakout-gs boards shipped with FB2 not installed. The newer
ones ship with it installed. I guess removing FB2 is easier for most
people than ordering one and installing it.

-- 
Dave Hylands
Vancouver, BC, Canada
http://www.DaveHylands.com/