[SI-LIST] Re: Altera PDN Tool
- From: "Allen Mayar/EXTON/USA/SALES/KEMET/US" <allenmayar@xxxxxxxxx>
- To: Leonard Dieguez <ldieguez@xxxxxxxxxx>
- Date: Wed, 22 Jul 2009 13:46:25 -0400
Content-Type: text/plain; charset="US-ASCII"
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At one time, the industry accepted that ESL was constant with frequency,=20
but we now know that is not true. We did see that the inductance varied=20
with measuring the mounted capacitor as opposed to the fixtured component, =
and for the most of the manufacturers, the measurements are on mounted=20
components as this represents the use conditions.
In the higher capacitance structures, we've been able to see that=20
inductance decreases to some asymptotic level (depending on case size)=20
that we were not able to measure with lower values. Because of this,=20
where the manufacturer measures the ESL may also introduce additional=20
variance between their ratings for similar devices. Some measure the ESL=20
at self-resonance (higher ESLs as KEMET reports) and others measure well=20
above self-resonance"lower is better". If a manufacturer specifies an ESL =
for all capacitance values in a case size as constant, then they are=20
using the ESL well above self-resonance. There are cases where this is=20
true, and in their catalogs, they'll include Impedance versus Frequency=20
responses for multiple capacitance values. Based on the capacitance=20
value, and the self-resonance of the Impedance plot, the derived ESL does=20
not match the "claimed" ESL.
The fact is that both of these are incorrect. The ESL does decay from the =
self-resonant frequency to well above this frequency. The theory is that=20
at self-resonance, the current is spread fairly evenly through the height=20
of the chip, but as frequency increases, the loop compresses until the=20
current is compressed into a minimized loop in the component. The=20
discrepancies in low frequency ESL and high frequency ESL is greatest for=20
those components utilizing the full height of the chip for the electrodes=20
(higher capacitance).
Within the next six months, we will be introducing a variable ESL model=20
in our Spice program, concentrating on the higher capacitance values at=20
first. Attached is a layout of the model which incorporates an "RL"=20
circuit in place of a single, fixed "L" component which will simulate this =
decaying ESL. In lower frequencies the ESL is based on a summation of L1=20
through L4, but in higher frequencies, L1 and L2 are the only inductive=20
elements, with L1 representing the termination and pad inductances. The=20
parallel resonance is factored by L2 and C2, and a secondary series=20
resonance by L1 and C2. Instead of replacing the existing model, this=20
model may be optional to the existing model.
=20
From:
Leonard Dieguez <ldieguez@xxxxxxxxxx>
To:
Joel Brown <joel@xxxxxxxxxx>, "si-list@xxxxxxxxxxxxx"=20
<si-list@xxxxxxxxxxxxx>
Cc:
John Oh <JOH@xxxxxxxxxx>
Date:
07/21/2009 01:35 PM
Subject:
[SI-LIST] Re: Altera PDN Tool
Sent by:
si-list-bounce@xxxxxxxxxxxxx
Joel,
I'm not 100 % sure what manufacturer was used when those values where=20
input to the tool but probably AVX or Murata. The values do not represent=20
the mounting inductance since the tool calculates that depending on the=20
mounting style and dimensions that are input to the tool. You can also=20
change your library or use "user values" for ESL /ESR. As with any other=20
EDA tool Garbage in equals garbage out. So check the values for the caps=20
that you are actually using and also check things like the stack up=20
heights Via placement and diameters and trace widths.
Leonard Dieguez
High Speed IO Applications,
Altera Corporation
9330 Scranton Road, Suite 400
San Diego, CA 92121
ldieguez@xxxxxxxxxx
858.202.3511 (office)
"There are two kinds of engineers - those who have signal integrity=20
problems, and those who will." - Eric Bogatin.
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]=20
On Behalf Of Joel Brown
Sent: Monday, July 20, 2009 5:17 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Altera PDN Tool
I have been playing around with the Altera PDN tool.
When I look at the ESR and ESL values on the Library page it seems the
values match very closely with AVX SpiCap3 which makes me think that is=20
were
the values came from.
When I used Kemet's spice program I get values that are quite different.=20
One
which stood out was an ESL of 1.9nh for a .01uF 0402 capacitor.
So it makes me wonder if I use the values in the Altera library if the
results are going to be anywhere close to reality especially if we are
buying capacitors from Kemet or another vendor.
I am assuming the ESL values in the Altera library don't include the
mounting inductance since they model that separately.
Is there any information comparing ESL from different capacitor vendors=20
for
0402 or any other size capacitors?
Thanks - Joel
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