[SI-LIST] Re: help me
- From: steve weir <weirsi@xxxxxxxxxx>
- To: zhang_kun@xxxxxxxxxx, a.ingraham@xxxxxxxx
- Date: Fri, 03 Feb 2006 16:50:52 -0800
Zhangkun with today's really low voltage CMOS devices, and a board that
doesn't have much in the way of resistors across the rails, a meter will
charge up the power supply to the point that the transistors start going
into the linear region. A supply with a variable current limit and an
Ammeter is really a better way to go.
Steve.
At 08:21 AM 2/4/2006 +0800, zhangkun 29902 wrote:
>Dear Andy
>
>The common multi-meter is of 12V. Is there any multi-meter of other voltage?
>
>Checking short or not in the PCB is really a problem in power integrity
>analysis. We are often afraid that the PCB is short when we are setting
>the testing point.
>
>Best Regards
>
>Zhangkun
>2006.2.4
>
>
>
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>----- Original Message -----
>From: Andrew Ingraham <a.ingraham@xxxxxxxx>
>Date: Saturday, February 4, 2006 0:38 am
>Subject: [SI-LIST] Re: help me
>
> > > after I have populated that 3 dsp I have checked between the 1Vpwr
> > > supply and gnd resistance is only 3 ohms
> > >
> > > my 1v pwr section is 20A design
> >
> > "Only 3 ohms?" How much resistance did you expect to measure?
> >
> > 3 ohms would mean 0.33 A (if the resistance were linear), far less
> > than the
> > power supply's 20 A. If you expected 10 A in normal operation, the
> > resistance should be 0.1 ohm (again, if it were linear) at 1 V.
> >
> > Because IC components are nonlinear, how much resistance you measure
> > strongly depends on the ohmmeter's applied voltage. (Most
> > ohmmeters don't
> > apply a voltage, so don't expect a fixed value from your meter.)
> >
> > Regards,
> > Andy
> >
> >
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