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

  • From: "Sogo Hsu" <sogo.hsu@xxxxxxxxxxx>
  • To: si-list@xxxxxxxxxxxxx
  • Date: Thu, 14 Apr 2005 01:37:22 -0000

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?
I think the solution is available owing to it can provide the 
required voltage level for full loading operation.

Thank you.

Best Regards,

Sogo Hsu, Ph. D.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Simulation center/Foxconn
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

--- In si-list@xxxxxxxxxxxxxxx, steve weir <weirsi@xxxx> wrote:
> 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=0.3V. 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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