[SI-LIST] Re: Decoupling Using 3-Terminal Capacitor
- From: steve weir <weirsi@xxxxxxxxxx>
- To: ha324005@xxxxxxxxx, si-list@xxxxxxxxxxxxx
- Date: Tue, 31 May 2005 15:41:45 -0700
Himanshu, you will really need to simulate this including with elements
that represent the interconnect. I would personally be wary about the
450:1 capacitance ratio as an invitation to a big antiresonant peak. Most
of the three terminal feed throughs that I am familiar with also have very
limited current handling capacity and high ESR.
Unless you are going to design a coupled multipole network, where you are
trying to flatten out the response ( see any of Larry Smith's excellent
papers on that approach ), SRF should not be your first concern. Rather
mounted inductance should. By way of example, we could take two capacitors
that really exist in the market today:
10uF 30mohm 200pH mounted inductance 3.6MHz SRF
10nF 120mohm 1nH mounted inductance, 50MHz SRF
Which performs best at 50MHz the SRF of the second capacitor? It is the
10uF part by almost 2:1. So given that you wish to design your network
with just a couple of capacitors, I would start with the mounted inductance
target that you need to meet, then the capacitance, and finally
consideration of damping as necessary. If you can't get all that you need
with one type of capacitor then carefully add additional larger devices to
extend the frequency reach down as far as you require.
Steve.
At 02:45 PM 5/31/2005 -0700, Himanshu Arora wrote:
>Hello,
>I am making a prototype PCB where in there are
>multiple VDDs.
>
>The Power Supply filter network looks somewhat like
>the one shown in the figure attached in text file.
>Instead of 2 terminal caps I plan to use the
>3-terminal cap. The 3-terminal caps are from Murata.
>
>The reason of using 3-terminal caps against 2-terminal
>Multi-layer-ceramic caps is that they offer lower ESR
>at SRF, their lead inductance is lower and their SRF
>is higher for the comparable cermic cap in value and
>case size. The reason I am connecting the two
>3-terminal caps in series is to offer a lower
>impedance across a wide range of frequencies.
>
>I would like to have your views and inputs for the
>above arrangement. Thanks.
>
>Sincerely
>
>Himanshu
>
>
>
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>-- Attached file included as plaintext by Ecartis --
>-- File: 3tcap.txt
>-- Desc: 2302733855-3tcap.txt
>
>
> VDD C1 C2
> ---- ----
> |--------Ferrite------------------------------------VDDA
> | ---- ----
> | | |
> | | |
> | GND GND
> |
> | ---- ----
> |--------Ferrite------------------------------------VDDD
> | ---- ----
> | | |
> | | |
> GND GND
>
>
>C2 = 2200pF (NFM21CC222R1H3)
>C1 = 1uF (NFM21PC105B1A3)
>
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