I should clarify the major problem between I.T. safety requirements and the USB spec, as an LPS.
USB 2.0, 7.2.1.2.1 Over-current Protection: The over-current limiting mechanism must be resettable without user mechanical intervention. Polymeric PTCs and solid-state switches are examples of methods, which can be used for over-current limiting. IEC/UL/EN 60950-1, 2.5 Limited power sources: Where an overcurrent protective device is used, it shall be a fuse or a non-adjustable, non-autoreset, electromechanical device. luck, Brian > -----Original Message----- > From: Brian O'Connell [mailto:[email protected]] > Sent: Friday, December 17, 2004 6:58 AM > To: Carpentier Kristiaan; ieee pstc list > Subject: RE: USB interface Limited Power source ? > > > For Information Technology: only if the device that > ultimately supplies the > power has installation instructions that states Conditions of > Acceptability > for meeting requirements of an LPS; and if there is > supporting test data in > the CBTR, agency FUS report, etc. > > Also, the USB 2.0 (see section 7) standard requires that > connected devices > limit their power consumption, and that the bus be able to > detect a long > rise-time caused by overload. But, the USB spec does not > address I.T. safety > considerations of the host as an LPS. > > luck, > Brian > > > -----Original Message----- > > From: Carpentier Kristiaan [mailto:[email protected]] > > Sent: Friday, December 17, 2004 3:23 AM > > To: ieee pstc list > > Subject: USB interface Limited Power source ? > > > > Hi group, > > > > The USB standard 1.1 or 2.0 defines that a USB host device > > must have an overcurrent protection " for safety reasons". > > If the aggregate current exceeds a preset value, which is 5.0 > > A, then the over-current protection circuit shall remove or > > reduces power to the attached devices. > > > > The above definition looks quite similar to the requirements > > of LPS in IEC60950-1 but the wording LPS is not explicitely > > mentionned in the USB spec. > > > > Q: Can I assume that a USB interface is LPS ? Is there any > > other evidence available to support this view ? > > > > Thanks, > > Kris This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
