Sogo, you ae welcome. From my interpretation of the specification,=20 everything is acceptable so long as the voltage is always between 4.75V and= =20 5.25V. So, your units should be passed. Regards, Steve At 09:30 AM 4/14/2005 +0800, Sogo Hsu wrote: >Steve, > >Thank you for your prompt response. I realize what you mean. We also prefer >to align the center for no loading at 5V nominally. Sometimes, it is hard >to achieve the goal owing to some design issues, such as the real estate >and number of ports. As a result, we got a trade-off to enhance the power >supply slightly. As I mentioned previously, USB 2.0 standard did not >specify the tolerance. It only required a 4.75 minimum input voltage. If >the power supply for no loading is absolutely at 5.1V, I wonder whether the >solution can be treated as PASSED or FAILED in voltage drop test? > >Thank you. > >Best Regards, > >Sogo Hsu, Ph. D. >~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ >Simulation center/TEC/PCEBG/Foxconn >~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > >=20 > > steve=20 > weir=20 > > <weirsi@xxxxxxxxx =A6=AC=A5=F3=A4H=A1G=20 > sogo.hsu@xxxxxxxxxxx, si-list@xxxxxxxxxxxxx > m> =B0=C6=A5=BB=A7=DB=B0e=A1G= =20 > > =A5D=A6=AE=A1G Re:= [SI-LIST]=20 > Test criterion of USB voltage drop test > 2005/04/13=20 > 08:37=20 > > PM=20 > >=20 > >=20 > > > > > >Sogo, there are several different values offered. > >A host hub must provide no more than 5.25V and no less than 4.75V at the >connector output for 0 load and 500mA load respectively at all >times. Refer to section 7.2.2 > >Your 4.80V - 5.1V sounds fine provided that is over temperature and >time. I would be inclined to center that at 4.85V - 5.15V nominally. It >sounds like your test house has misinterpreted the +/-0.25V total tolerance > >as +0/-0.25V tolerance for loading only. That is both overly pessimistic >and overly optimistic as the spread is narrower than it needs to be, but >neglects initial accuracy and aging errors. > >Steve > >At 10:47 AM 4/13/2005 +0000, Sogo Hsu wrote: > > >Hi, USB Gurus, > > > >Currently, we meet an issue in developing USB-IF 2.0 system. The > >voltage drop test result indicated the voltage for no loading and > >full loading is 5.1V and 4.8V, respectively. Obviously, the voltage > >drop is 5.1-4.8=3D0.3V. Someone said the test criterion for voltage > >drop test is 250mV. Accordingly, the test result indicated the USB > >system failed in voltage drop test. However, in USB 2.0 spec., the > >standard only defined the voltage drop budget has to be greater than > >4.75V. I realized that it is better if we can design a power > >delivery system with 250mV voltage drop. However, I think it is also > >available if we enhanced the power supply voltage slightly. Do you > >have any comment? I truly appreciated your feedback. Does the test > >result pass or fail in voltage drop test? > > > >Thank you for your helps in advance. > > > >BRs, > > > >Sogo Hsu, Ph. D. > >Simulation Center > >Foxconn > > > > > > > >------------------------------------------------------------------ > >To unsubscribe from si-list: > >si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > > > >or to administer your membership from a web page, go to: > >//www.freelists.org/webpage/si-list > > > >For help: > >si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > > > >List FAQ wiki page is located at: > > http://si-list.org/wiki/wiki.pl?Si-List_FAQ > > > >List technical documents are available at: > > http://www.si-list.org > > > >List archives are viewable at: > > //www.freelists.org/archives/si-list > >or at our remote archives: > > http://groups.yahoo.com/group/si-list/messages > >Old (prior to June 6, 2001) list archives are viewable at: > > http://www.qsl.net/wb6tpu > > ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu