[SI-LIST] Re: Test criterion of USB voltage drop test

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
> >
> >
> >
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