RE: [SI-LIST] : ESR and Q factor

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From: Cruz, Jose (Jose.Cruz@compaq.com)
Date: Thu Sep 21 2000 - 16:32:14 PDT


The 10uF value is quite common today with either X5R or Y5V dielectric.
Both at 6 or 10V. Some companies are going as high as 22uF. The X5R
will be a nice replacement for a Tantalum but not the Y5V. A 10 uF, 10
volts, Y5V, at 3.3V and 40 degrees C will probably have 50% of the rated
capacitance.

This probably have to do with your poles and zeros. They will move a lot
by this change.

Jose

-----Original Message-----
From: Thomas Jackson [mailto:tjackson@fmi.fujitsu.com]
Sent: Thursday, September 21, 2000 6:52 PM
To: 'si-list'
Subject: FW: [SI-LIST] : ESR and Q factor

Where did you get a 10 uF ceramic capacitor. That value seem awfully large
for ceramic. Are you sure of the value?

Thomas L. Jackson, P.E.
Staff Product Development Engineer
Infotainment
Systems Solutions Group
FUJITSU MICROELECTRONICS, INC.
3545 North First Street
San Jose, CA 95134-1804
telephone: (408) 922-9574
facsimile: (408) 922-9618
http://www.fujitsumicro.com

-----Original Message-----
From: Chris Cheng [mailto:chris.cheng@3pardata.com]
Sent: Thursday, September 21, 2000 3:08 PM
To: si-list@silab.eng.sun.com
Subject: [SI-LIST] : ESR and Q factor

dear friends,
     this is a strange one. i am using a linear regulator to
generate 3.3V on one of my board. the app note calls out using
a 10uf tantalum for output stability. being a simple minded
person, i decided to use a 10uf ceramic cap instead, thinking
it has a better esl and esr value. to my surprise, the
output breaks into huge oscillation. when i switch back to
using tantalum caps, the output quiet down instantly. the
same can be achieve if i use a >1 ohm resistor in series
with the ceramic cap.
    the question is, has anyone experienced similar sensitivity
in dc linear regulators (the part is lineartech lt1086)? why
do linear regulator has such sensitivity to q factors ?
    thanks in advanced.
    chris

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