[SI-LIST] Re: small signal AC model for Current mode DC_DC converters, for full PDN simulation
- From: earl albin <earlalbin@xxxxxxxxx>
- To: "Allen Mayar/EXTON/USA/SALES/KEMET/US" <allenmayar@xxxxxxxxx>
- Date: Tue, 24 Mar 2009 09:48:27 -0700
Istvan:
I looked at the current mode simulator, well, ??? Anyway there is a better
way to do that and it even alows mixing of current mode and voltage mode
(slope comp). So technically there is only one model if the current mode
slope comp is maxed out, i.e., no current feedback. The model is very simple
(key uses a -R in the current loop) and depicts the complex conjugate
pairs in the current. Again it's very simple. Let me dig it up and send you.
On Mon, Mar 23, 2009 at 7:48 AM, Allen Mayar/EXTON/USA/SALES/KEMET/US <
allenmayar@xxxxxxxxx> wrote:
> Istvan:
> Regarding the RLC lumped models for decoupling caps, to avoid errors in
> Electrolytic capacitors (Tantalum/Aluminum and polymers of both) it is
> helpful to plot a more complex model that considers the RC ladder effect
> (to mimic the capacitance loss with the increased frequency). Also for low
> ESL<1.2nH it is important to include a RL network to mimic decaying ESL
> with increasing frequency.
>
> You can import the Electrolytic models that takes RC ladder effect into
> consideration from the site:
> http://www.kemet.com/kemet/web/homepage/kechome.nsf/weben/kemsoft
>
> Instructions:
>
> http://www.kemet.com/kemet/web/homepage/kechome.nsf/file/KEMETSpiceman361x.pdf/$file/KEMETSpiceman361x.pdf
>
>
>
> Kind Regards
> Allen Mayar
>
>
>
> Be gentle with your ecosystem, print only when necessary
>
>
>
>
>
>
> "Istvan Nagy" <buenos@xxxxxxxxxxx>
> Sent by: si-list-bounce@xxxxxxxxxxxxx
> 03/22/2009 06:22 PM
>
> To
> <si-list@xxxxxxxxxxxxx>
> cc
>
> Subject
> [SI-LIST] small signal AC model for Current mode DC_DC converters, for
> full PDN simulation
>
>
>
>
>
>
> Hi
>
> I would like to model a power distribution system in frequency domain with
> a
> spice-like AC analysis, with all elements of it, together.
> For decoupling capacitors, I can use RLC lumped models, for IC pins
> something similar, for power planes and package planes, I can use an
> electromagnetic simulator to create a touchstone file that I can import
> into
> the program (QUCS, or Agilent ADS).
> But, for the voltage regulator, I think I have to create a small signal
> model to include in the simulation as a subcircuit. This model must have
> the
> same output impedance versus frequency response, as the original DCDC
> converter has, nothing else hast to be the same (switching circuits are
> not
> needed in the model, nor correct voltage levels). I dont want to model the
>
> DCDC converter with a single inductance or similar model, but put the
> whole
> control loop equivalent circuit into the simulation. the whole thing is
> described here:
> http://www.buenos.extra.hu/download/PowerIntegrityDesign_prj.rar (there is
> a
> pdf in it, and some circuit files) The "circuit" is all the models and
> elements of the PDN together.
>
> For a voltage mode converter, I think it is quiet straightforward how to
> make the equivalent circuit (
> http://www.buenos.extra.hu/download/voltagemode.jpg ), but for a current
> mode converter, it is trickier. My assumption was this: I read somewhere
> that a current mode converter has a double pole at the half the switching
> frequency, and a single pole at the 1/(2*TT*R_load*C_out). So, based on
> this, I made an equivalent circuit which has the same poles and no zeroes,
>
> so the same transfer function:
> http://www.buenos.extra.hu/download/currentmode.jpg The circuit element
> parameters are automatically calculated based on the provided switching
> frequency, load current, some other elements are coming from the original
> schematics, like the compensation RC networks... Maybe this way of
> modelling
> is not perfect for this purpose, but I think it's better than just using a
>
> single inductor (or an RLC model) for representing the whole DC/DC, or
> than
> guessing about the transient response.
>
> Is this model correct, or if not, how should I make it to be correct?
> I am not shure in this part.
>
> regards,
> Istvan Nagy
> CCT, UK
>
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