[SI-LIST] Re: Measurement peaks of current.
- From: "Jim Antonellis" <janton@xxxxxxxxxxxxxxxxxx>
- To: <tal_segev@xxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Wed, 4 Aug 2004 19:42:19 -0400
Tal,
I will probably also learn a lot when the PDS gurus chime in,
but count me in the naive group.... the boards we design, as=20
reference/characterization/demo boards for our chip sets, employ
4-port milli-ohm precision resistors for making power measurements.
Having said that, I must note the following:
I believe these measurements are low frequency in that they
are hopefully "decoupled" from the high frequency transients=20
that my cache of decoupling provides (die, chip and plane).
That is, the current profile has been smoothed out.
With all the caveats about making measurements (loop area etc)
I also believe scope isolation is needed in that both sides of
the resistor are at some potential relative to ground, and if
you connect one of the grounded scope probes I think you smell
smoke! Why not use a diff probe?
As far as another way of measuring power rails, we also use
Agilent power supplies that provide such information on their
LCD display (e.g 6654A)
Jim
-
Jim Antonellis jim.antonellis@xxxxxxxxxxxxx
Sandburst Corp www.sandburst.com
Office: 978.689.1669=20
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-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Tal Segev
Sent: Wednesday, August 04, 2004 4:34 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Measurement peaks of current.
Hi all,=20
I'm designing an embedded system with 8 DDR-SDRAM
(DDR-1) chips, large FPGA, CPU & so on. Due to the
amount of current gorges on the design, the result of
power calculation for this board is about 45W, without
the VTT and not considering the voltage regulators
efficiency, (a beet less then a lamp). I personally
predict that this design will use about 25W in
average.
I need to measure the current, especially the peaks of
the current; I'm considering using a serial 1.5mOhm
power resistor to measure the current through a scope.
So (finally), my questions are (I have lot of them).
* Is it that simple to measure the current, or am I
naive?
* Should I use some OP-Amps to isolate the scope from
the power?
* should I use active probe, or simple probe will
content?
* Can I avoid using a power resistor (its size is
huge, even the SMD)?
* Can any one suggest some other way to measure the
current?
Thanks for the patience,=20
Tal
=20
=09
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