[SI-LIST] Re: small signal AC model for Current mode DC_DC converters, for full PDN simulation
- From: earl albin <earlalbin@xxxxxxxxx>
- To: Istvan Nagy <buenos@xxxxxxxxxxx>
- Date: Tue, 24 Mar 2009 10:46:40 -0700
Istvan:
____________________________________________________________________
This model must have the
same output impedance versus frequency response, as the original DCDC
converter has, nothing else hast to be the same
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This is actually quite simple, if you understand and model converters and
especially if say the input voltage is static while the load is dynamic. If
you tell me what your purpose is for the model I can assist you with a
solution.
Regards,
Earl
2009/3/22 Istvan Nagy <buenos@xxxxxxxxxxx>
> 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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