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Rev. A, October 2003

©2003 Fairchild Semiconductor Corporation

6. Simulation Convergence

The self-heating model was tested under numerous circuit configurations. It was

found to be numerically stable. Failure to converge can occur under some large signal

simulations if PSPICE’s setup option ABSTOL setting is less than 1µA.

UIS simulations [10] were performed on a Dell Latitude CSx having a 500MHz Pen-

tium III processor with 256MB of RAM. Windows 2000 was the operating system used

with virus scan software enabled. PSPICE Schematics version 9.1 was used.

Simulation time results were:

- standard model = 7.9s

- self-heating model = 13.7s

Simulation time will be longer with the self-heating model when significant and rapid

junction temperature variation occurs. This is a result of the dynamic interaction from

the junction temperature feedback on the MOSFET temperature dependent parame-

ters.

7. Future Model Developments

Minor inaccuracy is introduced if previously published Fairchild Semiconductor MOS-

FET models are modified to become self-heating models, but are well within device

parametric tolerance (not demonstrated in this paper). The inaccuracy can be elimi-

nated by including the variable T_ABS=25 in the level-1 NMOS MOSFET during

device specific model calibration, permitting full compatibility of the model with the

new self-heating model. This term was included for the standard MOSFET model

calibration of the FDP038AN06A0. Temperature dependency of the self-heating

model intrinsic body diode leakage current could be introduced by adding a junction

temperature dependent current source across the body diode.

8. Conclusion

The self heating PSPICE power MOSFET macro-model provides the next evolution-

ary step in circuit simulation accuracy. The inclusion of a thermal model coupled to the

temperature sensitive MOSFET electrical parameters results in a self-heating

PSPICE MOSFET macro-model which allows increased accuracy during time domain

simulations. The effect of temperature change due to power dissipation during time

domain simulations can now be modeled.

The modeling modification concepts introduced are non-proprietary and may be

adapted to MOSFET SPICE models from any manufacturer. A methodology for cali-

brating a MOSFET model using parametric data was described. Adherence to the cal-

ibration sequence yields a highly accurate model.