SIMPLORER User Manual V6.0 - FER-a

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154 Modeling with Circuit Components
SPICE Tolerances in SIMPLORER
SPICE-compatible models set their convergence parameters from SIMPLORER:
• RELTOL is taken from LDF on the SIMPLORER TR parameters, scaling by 0.01 to convert
LDF from percent. LDF is used even for the SIMPLORER DC analysis, because the same
code executes both DC and Transient analysis in the SPICE models.
• ABSTOL is the default value scaled by SIMPLORER IEmax or Emax. For transient analysis,
ABSTOL=1e-12 * IEmax / 1e-3, because 1e-3 is the SIMPLORER default value for
IEmax. For DC analysis, including that which precedes AC analysis, ABSTOL = 1e-12 *
EmaxDC / 1e-3. For AC analysis, ABSTOL = 1e-12 * EmaxAC / 1e-6, but it has no effect
in the SPICE model execution.
• VNTOL is also scaled by SIMPLORER VEmax or Emax. For transient analysis, VNTOL =
1e-6 * VEmax / 1e-3. For DC analysis, VNTOL = 1e-6 / EmaxDC / 1e-3, and for AC analysis,
VNTOL = 1e-6 / EmaxAC / 1e-6.
• CHGTOL is the default value scaled by the ABSTOL * VNTOL product. CHGTOL = 1e-14
* ABSTOL * VNTOL/1e-18.
• After getting ABSTOL, VNTOL, and CHGTOL, the minimum values are limited to 100
times less than their SPICE defaults. ABSTOLmin = 1e-14, VNTOLmin = 1e-8, and
CHGTOLmin = 1e-16. There are no maximum values for ABSTOL, VNTOL, and CHG-
TOL.
• There are no minimum or maximum limits on RELTOL.
• GMIN is fixed at 1e-12, and TRTOL is fixed at 7.
Recommendations
The main parameter for users to adjust would be LDF, just as the main SPICE parameter to
adjust would be RELTOL. The suggested starting value is 1%, and later decreasing to 0.1% for
more accuracy. The default behavior of the SPICE-compatible models will be RELTOL=0.01
instead of RELTOL=0.001, but all other default convergence parameters are the same as in
SPICE 3f5.
The DC analysis of a SPICE-compatible model executes the same code as for a transient analysis,
and it will use RELTOL (LDF) from the SIMPLORER transient parameters. This value
should be reviewed when running a DC analysis.
In most cases, the SIMPLORER default values of 1e-3 for IEmax and VEmax will work with
the SPICE-compatible models. However, it may be necessary to reduce them for acceptable
results in some cases.
SPICE 3f5 users are sometimes advised to allow up to 500 iterations for DC and transient analysis.
If convergence becomes a problem, these higher limits can be set directly in the SIM-
PLORER simulation parameter ITERATMAX.
Temperature Effects on SPICE-Compatible Models
SPICE semiconductor device parameters can be adjusted for temperature. If you define the
component temperature different from the default value of 27 °C, that temperature is used.
Otherwise the model ambient temperature, which is defined as simulation parameter, is used.
If you change the model ambient temperature in SIMULATION>PARAMETERS «General», but
you want a component to stay at the default value of 27, then you must change that component
temperature to a slightly different value, such as 27.01. This is necessary of how the library
must handle default values.