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

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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