Re: MLCC experience/suggestions?


"John Larkin" <jjSNIPlarkin@xxxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:1c7q73930i6f6qkodo2had2pq91k15o89g@xxxxxxxxxx
On Fri, 22 Jun 2007 21:09:47 -0600, "starfire"
<starfire151@xxxxxxxxxxxx> wrote:

Does anyone have any experiences (good or bad) with using MLCC-type caps
for
input power / voltage regulator applications? I'm using 22uF Tantalums
right now and have reduced (but not eliminated) some heavy switching
transients. The MLCC looks good in terms of no polarization and reduced
package size for the capacitance rating.

Is there a source for these caps (in 47uF or 100uF flavors) at prices
lower
than DigiKey? DigiKey wants $23.48 for ten 100uF, 6.3V caps. I realize
this is a relatively new technology but has anyone run across a more
inexpensive source?

Thanks.

Dave


Ceramics are great, and values like 10 or 22 uF are affordable. But a
lot of regulators will oscillate into a big ceramic load, including
most LDOs and LM337.

John


Now that's EXACTLY the kind of information I was looking for! Thank you!

So often people get sidetracked by picking on the exact verbiage used to
format the questions that they overlook the context of the question...

I had a problem with switching transients on an LDO which a larger input
capacitor seemed to reduce. I had been using a 1uF ceramic on the
input-side and a 1uF ceramic on the output-side of a TC1108 LDO regulator.
Max current draw at 3.3VDC was about 100mA. Per great suggestions form this
group, I inserted a larger 22uF Tantalum on the input-side and the problem
was significantly reduced. While the switching transient was reduced to the
point of not causing a problem with board operation, it was still there, but
greatly reduced in amplitude. The voltage dip only dropped to about 2.5VDC
from the nominal 3.6VDC input and there was virtually no overshoot when the
transient ended about 2usec later. I had thought to increase the size of
the input cap to 47uF, 68uF, or even 100uF. I also just found out about
MLCC caps (I'm sorry... I must have been living a sheltered life:) ) and
saw the reduced size for the footprint as well as the non-polarized
components.

Since these components are relatively high cost ($23.48 for 10 parts from
DigiKey), would I be wasting time and money to try something like the 100uF
1206 device for the input-side LDO filtering?

Thanks.

Dave


.

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