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Decoupling caps

J

James Meyer

Jan 1, 1970
0
What is the difference in series inductance between a 0603 1uF part
and a 0603 0.1uF ceramic part?

Best regards,
Spehro Pefhany

You can find 0603 0.1uF ceramics with 50 volt ratings. OTOH, 0603 1.0uF
ceramics are very hard to find at over 16 volts.

Jim
 
P

Paul Burridge

Jan 1, 1970
0
The reason is because once you start to get into high frequencies the
inductance of the cap (leads, end terminations, _winding_) starts to
matter and, generally, the higher the capacitance for a given family
of caps, the higher the inductance of the cap. At low frequencies it
doesn't matter much, but once you leave the slop of audio behind and
things start to get important, you'll eventually get to a point where
instead of soldering in bypass caps what you'll really be doing is
soldering in peaking coils, where some really interesting things start
to happen when you hit the self resonant frequency of the cap. Look
it up. Especially, think about what an aluminum electrolytic with
_coiled_ plates...

Er, yeah. Believe it or not, I do actually remember all this stuff
from your last discourse on the subject....
Remember I'm talking about SMDs in this case and to be precise, the
caps I bought are multilayer ceramics in 0603 cases (not sure if the
dielectric is X7R or Y5M, though) so forget about electrolytics; we're
about as far a way from them as one can be.
Right. Like you really _need_ an 0.1, but since you can't get one to
fit you'll settle for an 0.01 instead?

No, the other way around. I'm asserting that these 0603 1uF caps ought
to be good for decoupling purposes into the several Ghz region in
place of specified values of 0.1 and 0.01. Anyone see a problem with
that?
 
S

Spehro Pefhany

Jan 1, 1970
0
You can find 0603 0.1uF ceramics with 50 volt ratings. OTOH, 0603 1.0uF
ceramics are very hard to find at over 16 volts.

Jim

True enough, but most digital (and many analog) bypass applications
these days are for 5V or less. Even some inexpensive microcontrollers
such as the 60MHz LPC210x series are now running at 1.8V nominal on
the core and 3.3V on the I/O, so you don't have to be working with
massive GHz CPUs to be using sub-2V supplies. That (ARM7TDMI-S) core
is only 0.32mm^2 if made with a 0.13u process.

It's not hard to find X7R ceramic 1uF in larger sizes rated at 50V
100V, which is fine for input power bypass caps on small ~1MHz SMPS
buck regulators. I expect availability to increase in the near term,
so they may be appropriate for new designs.

Best regards,
Spehro Pefhany
 
J

John Woodgate

Jan 1, 1970
0
I read in sci.electronics.design that Spehro Pefhany <speffSNIP@interlog
What is the difference in series inductance between a 0603 1uF part and
a 0603 0.1uF ceramic part?

The inductance of the *traces* leading to the part may well be dominant
for 0805 parts.
 
J

John Woodgate

Jan 1, 1970
0
I read in sci.electronics.design that Paul Burridge
I'm asserting that these 0603 1uF caps ought
to be good for decoupling purposes into the several Ghz region in place
of specified values of 0.1 and 0.01. Anyone see a problem with that?

Yes. Trace length.
 
G

Genome

Jan 1, 1970
0
Paul Burridge said:
On Fri, 10 Sep 2004 18:55:39 -0500, John Fields

No, the other way around. I'm asserting that these 0603 1uF caps ought
to be good for decoupling purposes into the several Ghz region in
place of specified values of 0.1 and 0.01. Anyone see a problem with
that?

Why don't you **** off to fucking Google and fucking search for some fucking
data on some fucking capacitors and fucking see how fucking good they
fucking might fucking be at fucking several fucking gigafuckinghertz.

DNA
 
J

John Larkin

Jan 1, 1970
0
True enough, but most digital (and many analog) bypass applications
these days are for 5V or less. Even some inexpensive microcontrollers
such as the 60MHz LPC210x series are now running at 1.8V nominal on
the core and 3.3V on the I/O, so you don't have to be working with
massive GHz CPUs to be using sub-2V supplies. That (ARM7TDMI-S) core
is only 0.32mm^2 if made with a 0.13u process.

It's not hard to find X7R ceramic 1uF in larger sizes rated at 50V
100V, which is fine for input power bypass caps on small ~1MHz SMPS
buck regulators. I expect availability to increase in the near term,
so they may be appropriate for new designs.

Best regards,
Spehro Pefhany

Somebody now sells 100 uF 0805-size ceramic caps. Don't remember the
voltage, but it must be low.

John
 
P

Paul Burridge

Jan 1, 1970
0
I read in sci.electronics.design that Spehro Pefhany <speffSNIP@interlog


The inductance of the *traces* leading to the part may well be dominant
for 0805 parts.

What's that got to do with Speff's question, DataBoy?
 
P

Paul Burridge

Jan 1, 1970
0
I read in sci.electronics.design that Paul Burridge


Yes. Trace length.

WTF has that got to do with it if all other things are equal?? You're
introducing something into the question that wasn't there in the first
place! What makes you think that anyone would require different length
traces for 0603 and 0805 packages???
 
P

Paul Burridge

Jan 1, 1970
0
Why don't you **** off to fucking Google and fucking search for some fucking
data on some fucking capacitors and fucking see how fucking good they
fucking might fucking be at fucking several fucking gigafuckinghertz.

I'm supposed to be in your killfile, dummy. I've already reminded you
at least once. How many times do you need to be told?
 
S

Spehro Pefhany

Jan 1, 1970
0
At high frequencies, the impedances converge. You *can* use the SRF
notch to advantage in narrowband applications.
John

Would you consider using the notch in digital applications, say
picking it at the clock frequency?

Best regards,
Spehro Pefhany
 
J

John Larkin

Jan 1, 1970
0
Would you consider using the notch in digital applications, say
picking it at the clock frequency?

No. As JW notes, series resonant frequency will depend on layout a
lot, too. Besides, I depend on the pcb planes as the serious HF
bypass, and just scatter 0.1 or 0.33 uF ceramics around the board, not
necessarily close to any particular IC pins. The overall structure,
pcb planes + caps, seems to behave like one huge, fairly lossy lo-Z
transmission line, or a big low-Q capacitor maybe.

Seems to work.

John
 
F

Frank Miles

Jan 1, 1970
0
[snip]

http://rocky.digikey.com/WebLib/Panasonic/Web data/ECJ Series.pdf

Take a look at page 15, Only the impedance values are given, and it's for
0805 caps. Note that the ceramic material also has a significant effect on
impedance. Add in a little trace inductance, and the graphs will shift to
the left, likely enough to get close to my ballpark #'s.

It's interesting that they show Z vs. f for NPO and X7R/X5R types, but
don't have plots for the Z5R/Y5V family. Now what _was_ the dielectric
material on those 1uF's?

-frank
--
 

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