Re: Quick ESR answer needed

On Wed, 15 Aug 2007 15:24:55 -0700, Winfield Hill <hill@xxxxxxxxxxx>
wrote:

On Aug 15, 5:58 pm, John Larkin
<jjlar...@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
On Tue, 14 Aug 2007 09:51:38 -0700, Jim Thompson

<To-Email-Use-The-Envelope-I...@xxxxxxxxxxxxxxx> wrote:
Quick ESR answer needed...

Typical 0.22uF ceramic in low voltage application (5V max), what ESR
might I expect?

Client says 0.2 Ohms

I doubt that number, but don't have anything to base my doubt on.

What say yee all?

While I was waiting for The Board to show up, I cobbled up this:

http://s2.supload.com/free/Setup.JPG/view/

http://s2.supload.com/free/Ramp.JPG/view/

It's a 0.1 uF, 0805 cap soldered across a 50 ohm transmission line.
It's being driven from (we pause for this commercial message...)

http://www.highlandtechnology.com/DSS/P400DS.html

which is setup for 5 volts out, 50 ohms, so it's dumping a 100 mA step
into the cap with about a 1 ns risetime. The scope bandwidth is 20
GHz.

The first glitch is L di/dt, roughly estimated as 1.5 nH.
Extrapolating the slope back to the start gives very roughly 20
milliohms, but it's hard to resolve that small a resistance with this
rig. The glitch at about 10 ns is a cable reflection.

This cap is pretty much a dead short in the, say, 3 ns time frame.

John

My hp4192 Impedance Analyzer, outfitted with
an 16034E SMT fixture, used in average mode,
says a Panasonic 0.1uF 25V X7R 0805 cap has
C = 92nF, plus about 36-milliohms of esr.

If one eyeball extrapolates my slope down to about the midpoint time
of the inductive glitch, 40 milliohms isn't an unreasonable guess. At
least we aren't disagreeing by 2000:1 or anything like that!

John

.

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