[SI-LIST] Re: Decoupling capacitors
- From: Michael_Greim@xxxxxxxx
- To: chris.cheng@xxxxxxxxxxxx, si-list@xxxxxxxxxxxxx
- Date: Fri, 17 May 2002 08:07:06 -0500
With a small form factor cap with a small
esl, it is not surprising to see the
predominant effect on the overall mounting
inductance be mounting method. In the AVX
paper on capacitor parasitics, they discuss
a measured inductance of 870 pH. Without a
whole lot of work, one can mount a cap with
2-3 nH of inductance (longish traces fanned
out from the ends). Couple this with very low
esr and you will have the possibility of
pronounced anti-resonance points. Low esr with
high mounted esl is a bad thang.
Just my 0.02
best regards,
Michael Greim
-----Original Message-----
From: Chris Cheng [mailto:chris.cheng@xxxxxxxxxxxx]
Sent: Thursday, May 16, 2002 4:12 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Decoupling capacitors
I am also under the impression that the surface
mount pad and via structure on PCB will be the
larger inductance vs. the capacitor itself.
Any drop in inductance based on smaller capacitor
size will be small compared with the pad and via
inductance.
Chris
-----Original Message-----
From: Ray Anderson [mailto:Raymond.Anderson@xxxxxxx]
Sent: Thursday, May 16, 2002 2:02 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Decoupling capacitors
Another thing to consider regarding Y5V parts is the loss
of rated capacitance when DC bias is applied.
Y5V parts exhibit a loss of about 85% capacitance at a
bias level of 6vdc. i.e.: a 100uF part will actually
have about 15uF capacitance at 6 vdc bias.
X5R (which is similar to X7R) parts exhibit a 40% loss
of capacitance at 6vdc. A 100uF part will have 60uF
capacitance at 6vdc.
Be sure to understand all the curves on the data sheets
and ping your selected vendor for more detailed info.
-Ray Anderson
Sun Microsystems
>
>Decoupling capacitors 0603/X7R/100nF versus 0402/Y5V/100nF
>
>Although 0402 pkg. has less inductance (that matters), 100nF caps in that
>package are only available with Y5V dielectric and our EE has the following
>concerns:
>
>1. Self-resonant frequency is lower (5MHz for Y5V versus 20MHz for
>X7R)
>
>2. Limited temperature range (+22%-82% capacitance for Y5V versus
>+/-15% capacitance for X7R)
>
>
>Is it safe to use 0402 pkg. instead of 0603?
>
>
>Thanks,
>Alex
>-------------------------------------------
>Alexander Shapira
>Sr. PCB Designer
>Leitch Technology Corp.
>www.leitch.com <http://www.leitch.com>
>
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