Re: TL081/TL084 Model that accurately models Power Supply Current ??

From: Mike Engelhardt (nospam_at_spam.org)
Date: 11/29/04 

Date: Mon, 29 Nov 2004 21:43:47 GMT

Jim,

>>> I'm looking for a TL081/TL084 Model that accurately
>>> models power supply current.
>>>
>>> The models on TI's site are deadly INACCURATE :-(
>>
>> That vender opamp models don't steer current from
>> the supplies deals with their Boyle model ancestry.
>>
>> I would recommend using LTspice's Universal Opamp
>> model. It properly steers current from the supplies.
>> You specify Avol, GBW, slew rate, current limit,
>> phase margin, switch saturation voltage(how close
>> the output gets to the rails), offset voltage,
>> equiv. input voltage and current noise densities
>> and corner frequencies for the particular opamp.
>>
>> LTspice's Universal Opamp model does tend to be
>> better than many of dedicated PSpice-style opamp
>> models that get supplied by vendors based on the
>> Boyle model.
>
> I guess I need to finish refining my model ;-)
>
> I've added a lot of bells and whistles, but not
> yet the power-supply/load coupling.

The documentation on LTspice's Universal Opamp
model can be found in the schematic installed as

./examples/Educational/UniversalOpamp.asc

These models were recently updated in response
to extensive field testing.

They use a transconductance with a hyperbolic
tangent transfer function into the dominate
pole to model GBW and slew and also give some
onset of slew rate limited distortion as you
approach the slew limit. The same symbol can
model four different models each with increasing
complexity. If you forego the phi margin specification,
then level 2 is enough. It does Avol, GBW, slew rate,
current limit, switch saturation voltage, offset
voltage, equiv. input voltage and current noise
densities and corner frequencies with a single
internal node -- a technology otherwise unmatched
in circuit simulation.

--Mike