This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

AM3359: USB OTG operation with USB flash drive

Part Number: AM3359
Other Parts Discussed in Thread: TUSB320, BQ25886,

Hi

On our custom board we use USB1 of the AM335x in OTG mode. We have now realized that some USB flash are working while others do not.

Observing Vbus shows that the OTG volatge spikes are present when teh USB connector is open:

When connecting a flash drive (that is not working) Vbus looks like this:

So it appears as if the AM335x does recongnize that a device is connected. But after switching Vbus on for approx. 2 seconds the processor switches Vbis off again and this is repeated forever. Obviously something with the USB enummeration goes wrong. It makes no difference whether the USB flash drive is plugged in during run time of before the device is booted.

When connecting a working USB flash drive the shape of Vbus looks exactly the same with the only difference that Vbus does not swich off after 2 seconds.

Maybe I should mention that Vbus is controlled by the DRVBUS signal via a charger IC:


... and that there is switchable capacitor to comply with USB host specification:

Any idea why this does not work and how we could solve this issue?
Thank you for your reply!