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When to use VBUS monitoring | Cypress Semiconductor

When to use VBUS monitoring

Summary: 1 Reply, Latest post by VAVC on 19 Jun 2014 01:44 AM PDT
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MathMan's picture
2 posts


... another question.  I'm reading through the USBFS datasheet and a question now comes up.  The device that I'm working on is self-powered.  The datasheet makes me think that it's necessary, when this is the case, to have VBUS monitoring enabled.  For example, from the datasheet, "... however, for self-powered designs it is imperative for proper operation and USB certification that your device complies with this requirement."  This makes me think that, because this is self-powered, I must enable this.  My first question is simply, is this interpretation true?  This device will not be used outside my company so certification isn't a concern, but proper operation is.

The question is, following the first, if I must enable this, how am I to know which is the correct option to select?  Should I choose internal VBUS or external?

Incidentally, where is the documentation for the API that's generated?  I get the datasheet for the component alright, but where do I find docs about these functions that are written for me?


VAVC's picture
Cypress Employee
506 posts

Hi ,


As per USB 2.0 spec, the device shouldn't drive data lines when upstream port is not connected. In may cause some enumeration problems. That's why you have to implement VBUS monitoring for szlef powered devices


I assume that you are using the PSOC part. So please post the response in the PSOC related forum to get information about the API's.




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