[SI-LIST] Re: controlled ESR capacitors or series resistors
- From: Anto Davis <antokdavis@xxxxxxxxx>
- To: Istvan Novak <istvan.novak@xxxxxxxxxxx>
- Date: Sun, 28 Dec 2014 14:28:18 +0530
I understood that, the L is the larger value capacitor's and the C is the
smaller value capacitors.
I had gone through your paper on Distributed matching, where u have
mentioned about Q<<1, which corresponds to the overdamped case. If the
design too much overdamped, it will need more number of capacitors right?,
which leads to overdesign right??
Another doubt, I have is, suppose I am using an X7R capacitor, which has
+-15 tolerance, then, when too many capacitors are used, for a PDN design,
should I try for a Monte Carlo simulation??? Or is there any better or
easier method to find out the worst case?
Anto
On Sat, Dec 27, 2014 at 10:03 PM, Istvan Novak <istvan.novak@xxxxxxxxxxx>
wrote:
> Anto,
>
> Just to clarify something: when the ESR^2=L/C formula is used for
> matching, C and L refer to different parts' capacitance and inductance. C
> is the capacitance of the higher-frequency capacitor and L is the
> inductance of the lower-frequency capacitor. When the formula is applied
> to the same part, you may want Q<<1 for best result.
>
> Yes, ESR is frequency and temperature dependent. Frequency dependence is
> actually lower than what you get in regular MLCC; the temperature
> dependence depends on the technology how ESR is raised. In that sense the
> solutions are different from the two MLCC vendors offering controlled-ESR
> capacitors today; TDK and Murata.
>
> Regards,
>
> Istvan Novak
> Oracle
>
>
>
> On 12/27/2014 2:38 AM, Anto Davis wrote:
>
> Thanks Romi Mayder,
>
> That was a helpful information.
>
> It has ESR from 0.1 to 1 ohms.
> The critical or over damping should be chosen for the design. If, plane
> spreading L is neglected, if the mounting inductance is the main culprit.
> ESR^2 > L/C, so it is also a function of Capacitance also, more clearly,
> capacitance/volume. So if I can get higher C value per volume, that has
> better chance of giving critical/over damped condition. The L < 0.01C for
> 0.1 ESR, So, 1 uF can have L of 10 nH and 0.1 uF can have 1 nH.
> If the design is for lower voltage (less than 1 V), C/volume can be
> higher, since the dielectric breakdown voltage can be lower. So the voltage
> is another design choice.
>
> In actual practice ESR varies with temperature and frequency, so the
> minimum should be taken for the design.
> I guess, the Murata specify the minium promising ESR, right?
>
> Thanks,
> Anto
>
>
> On Sat, Dec 27, 2014 at 5:40 AM, Romi Mayder <romi.mayder@xxxxxxxxxx>
> wrote:
>
>> Hi Anto,
>>
>> You may also find it helpful to check out the "LLR" series of controlled
>> ESR capacitors from Murata. Murata "LLR" series caps offer several
>> different ESR values for the same/similar capacitance value in the same
>> size package with nearly same inductance. You can get up to 1000mOhm of
>> ESR if you want/need it.
>>
>> Kind Regards
>> Romi
>>
>>
>> -----Original Message-----
>> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
>> On Behalf Of Istvan Novak
>> Sent: Saturday, December 20, 2014 10:28 AM
>> To: antokdavis@xxxxxxxxx; si-list@xxxxxxxxxxxxx
>> Subject: [SI-LIST] Re: controlled ESR capacitors or series resistors
>>
>> Anto,
>>
>> You know the answer :-) : it depends.
>>
>> Once you are through the design process and figured out what ESR for each
>> piece you want, you need to consider the required bandwidth of the part.
>> If you add resistance with a separate part, it will increase the inductance
>> of the structure, limiting its bandwidth. Usually if you need hundreds of
>> milliohms or higher, separate discrete parts tend to be OK or better, for
>> low milliohm values it is better to use a single-piece solution.
>>
>> Regards,
>>
>> Istvan Novak
>> Oracle
>>
>>
>>
>> On 12/19/2014 11:52 PM, Anto Davis wrote:
>> > Hi,
>> > For optimum flat PDNs, the series resistor should be equal to square
>> > root (L/C).
>> > Out of the two options (1: controlled ESR caps 2: adding series
>> > resistors to capacitors) which is more commonly chosen?
>> > Is there any other option available ?
>> >
>> > Thanks,
>> > Anto
>> >
>> >
>> >
>> >
>>
>>
>>
>
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