Did you ask the designer? Gerald
On Wed, Feb 19, 2014 at 7:33 AM, <[email protected]> wrote: > I was having flaky USB behavior on multiple BBB boards and so investigated > the USB Power control circuitry. Her is what I found. > > The Pull-Up resistor on the USB1_OCn signal has an invalid voltage > reading. The pull up should set the signal at 3.3V as the resistor is > attached to a 3.3V supply. (this was verified through measurement). The > value of the pull up is 10K as shown. > Essentially what I see is that during certain USB activity the main > processor will disable the USB1_DRVVBUS signal which turns off USB power. > My theory is that the voltage level on the USB1_OCn signal is close to the > value which would indicate an Over Current condition. > The processor then removes power and disable the USB bus. (this is my > theory but I am not positive on this) > > What is a fact is that the voltage on the USB1_OCn signal is at an > improper logic value for a 3.3 Volt IO signal. The processor will at times > remove the USB1_DRVVBUS signal hence removing USB power. > > I have watched the USB1_OCn signal while the processor removes the > USB1_DRVVBUS signal. It does not change value to 0 volts as would be > expected when a true over current condition occurs. I also forced the Over > Current condition by grounding the USB1_OCn signal to verify that the > processor will remove the USB_DRVVBUS signal when a truen OC event occurs. > It did remove the USB_DRVVBUS signal as expected. > > To investigate why the USB1_OCn signal was being held in an improper > state, I lifted Pin 5 of U8 removing the open drain driver. The voltage > remained at the incorrect logic level showing that the culprit is not U8. > > I tried to come up with a work around by lifting pin 4 of U8 and pulling > it high such that the processor could not remove the power from the USB > port. In this case the kernal will not recognize the USB port. During > boot, the USB_DRVVBUS signal never goes to a high state. I monitored this > signal even though it was not attached to U8. I believe the USB Bus > voltage is present at the main processor before the main processor wanted > it be there and during boot gets upset and does not enable the port. > > So.... > > Can anyone from Beagle explain why the voltage on R52 is sitting at 2.4 > volts? > > -- > For more options, visit http://beagleboard.org/discuss > --- > You received this message because you are subscribed to the Google Groups > "BeagleBoard" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > For more options, visit https://groups.google.com/groups/opt_out. > -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/groups/opt_out.
