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Ceramic Cap Ripple Current

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Tim Wescott

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Jan 31, 2012, 4:13:13 PM1/31/12
to
I'm looking at this cap:
http://search.digikey.com/us/en/products/GMK316F106ZL-T/587-1352-2-
ND/930704

The only thing the data sheet says about the ripple current is that it is
"high".

So -- is there a way to tell just how much ripple current the cap will
stand, short of buying 10000 of them and doing a study?

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com

Fred Bartoli

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Jan 31, 2012, 5:41:50 PM1/31/12
to
Tim Wescott a écrit :
> I'm looking at this cap:
> http://search.digikey.com/us/en/products/GMK316F106ZL-T/587-1352-2-
> ND/930704
>
> The only thing the data sheet says about the ripple current is that it is
> "high".
>
> So -- is there a way to tell just how much ripple current the cap will
> stand, short of buying 10000 of them and doing a study?
>

Don't know but I recently had 'bad' surprises with 0402 x7R caps.
Measuring them vs voltage led me to think those were Y5V caps, but those
were not. I think I've read somewhere it's related to dielectric thickness.

Y5V being what it is, even in bigger caps, check their value under
conditions similar to the final use. You may find lower values X7R will
do better. Then you add the temperature effects and...


--
Thanks,
Fred.

Fred Bartoli

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Jan 31, 2012, 5:53:48 PM1/31/12
to
Fred Bartoli a écrit :
When you look at the datasheet p14 you see impedance curves for that
very capacitor and min esr is circa 10mR. Now you can you the power
dissipation of a 0402 resistor as a start.


--
Thanks,
Fred.

John Larkin

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Jan 31, 2012, 6:14:32 PM1/31/12
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On Tue, 31 Jan 2012 15:13:13 -0600, Tim Wescott <t...@seemywebsite.com>
wrote:

>I'm looking at this cap:
>http://search.digikey.com/us/en/products/GMK316F106ZL-T/587-1352-2-
>ND/930704
>

Hmmm. Y5V. Might be lossy.


>The only thing the data sheet says about the ripple current is that it is
>"high".
>
>So -- is there a way to tell just how much ripple current the cap will
>stand, short of buying 10000 of them and doing a study?

Buy 10 and do a study?

There are people that make high-current RF caps. The classic was the
ATC porcelain parts, used in RF gear that would melt the solder off
regular ceramic caps. Lately they, and others (AVX, Johanson, ATC) are
making high-current-rated ceramics. They should have data sheets.

I'd recommend heat sinking the caps to a lot of copper, too. That
works for resistors. An 0603 resistor will run happily at half a watt
if you solder it to a couple of husky copper pours.


**********************************

John Larkin, President
Highland Technology, Inc

jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro acquisition and simulation

George Herold

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Feb 1, 2012, 11:48:03 AM2/1/12
to
Hi Tim, does this relate to the dissipation factor?

I’ve always been a bit confused by the difference between
ESR and the DF. I got some 10uF ceramics in the other day and gave
them the JL, step response test. (10 Volt step from 50 ohm source.)

First here’s a 10uF tant....(as a reminder)

Step into 10uF tant.

http://imageshack.us/photo/my-images/831/tek0047.png/
(so what’s the little up sloping bit before it turns linear)

10uF ceramic (X7R)

http://imageshack.us/photo/my-images/692/tek0048.png/
The wiggles are from my setup. Twice the ‘scope vertical gain.


and a 1uF X7R
http://imageshack.us/photo/my-images/823/tek0049.png/


George H.

John Larkin

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Feb 1, 2012, 4:22:12 PM2/1/12
to
On Wed, 1 Feb 2012 08:48:03 -0800 (PST), George Herold
<ghe...@teachspin.com> wrote:

>On Jan 31, 4:13 pm, Tim Wescott <t...@seemywebsite.com> wrote:
>> I'm looking at this cap:http://search.digikey.com/us/en/products/GMK316F106ZL-T/587-1352-2-
>> ND/930704
>>
>> The only thing the data sheet says about the ripple current is that it is
>> "high".
>>
>> So -- is there a way to tell just how much ripple current the cap will
>> stand, short of buying 10000 of them and doing a study?
>>
>> --
>> My liberal friends think I'm a conservative kook.
>> My conservative friends think I'm a liberal kook.
>> Why am I not happy that they have found common ground?
>>
>> Tim Wescott, Communications, Control, Circuits & Softwarehttp://www.wescottdesign.com
>
>Hi Tim, does this relate to the dissipation factor?
>
>I’ve always been a bit confused by the difference between
>ESR and the DF. I got some 10uF ceramics in the other day and gave
>them the JL, step response test. (10 Volt step from 50 ohm source.)
>
>First here’s a 10uF tant....(as a reminder)
>
>Step into 10uF tant.
>
>http://imageshack.us/photo/my-images/831/tek0047.png/
>(so what’s the little up sloping bit before it turns linear)

That's because a tantalum cap is a complex network, equivalent to a
bunch of dielectric absorption. The model is multiple RCs in parallel,
all with different time constants. The "ESR" then becomes frequency
dependent and really has no single value.

You can use the height of the initial step to estimate the ESR of all
the equivalent Rs (of the multiple RCs) in parallel.

Some people model a tantalum as a string of cascaded RCs, looking
kinda like a lowpass filter, but that's about equivalent.


>
>10uF ceramic (X7R)
>
>http://imageshack.us/photo/my-images/692/tek0048.png/
>The wiggles are from my setup. Twice the ‘scope vertical gain.

Needs more gain! The spike is ESL, probably, or test setup leads.

>
>
>and a 1uF X7R
>http://imageshack.us/photo/my-images/823/tek0049.png/
>
>

Needs more gain!

George Herold

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Feb 1, 2012, 10:03:31 PM2/1/12
to
The spike is what's left over from the 40MHz ringies I had before.
Now a cap on on BNC jack with x1 scope probe.
>
>
> >and a 1uF X7R
> >http://imageshack.us/photo/my-images/823/tek0049.png/
>
> Needs more gain!
Well then it's more than just hanging stuff off the function
generator.

George H.

>
> **********************************
>
> John Larkin, President
> Highland Technology, Inc
>
> jlarkin at highlandtechnology dot comhttp://www.highlandtechnology.com
>
> Precision electronic instrumentation
> Picosecond-resolution Digital Delay and Pulse generators
> Custom laser controllers
> Photonics and fiberoptic TTL data links
> VME thermocouple, LVDT, synchro   acquisition and simulation- Hide quoted text -
>
> - Show quoted text -

Jasen Betts

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Feb 1, 2012, 6:07:05 AM2/1/12
to
On 2012-01-31, Tim Wescott <t...@seemywebsite.com> wrote:
> I'm looking at this cap:
> http://search.digikey.com/us/en/products/GMK316F106ZL-T/587-1352-2-
> ND/930704
>
> The only thing the data sheet says about the ripple current is that it is
> "high".
>
> So -- is there a way to tell just how much ripple current the cap will
> stand, short of buying 10000 of them and doing a study?

You know the ESR and can compute the RMS ripple curent,
Compute I²R,
How hot does it need to get to dissipate that energy?
Is that too hot?

--
⚂⚃ 100% natural

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