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pspice model issue

tltoth

Hi,

I've a circuit to perform temperature analysis on which contains an NXP transistor PBHV9040T.
I downloaded the spice model from the NXP site h..p://www.nxp.com/documents/spice_model/PBHV9040T.prm
During temperature sweep pspice gives the following error message "simulation aborted because VJC is negative"
Then I simulated the output characteristic curves of the transistor and I obtained the same result.
This transistor gives negative VJC value above 54 Celsius. Since the SGP equations are provided on page 253 of pspcref.pdf
I calculated this parameter by hand and the result is the same as calculated by the program.
The initial value of the VJC is such a small as 0.102 which might cause the problem.
When I asked NXP for explanation they told that they use LTspice and there is no simulation problem with that.
So the question is whether the built in SGP equations are wrong whitin the PSpice or the NXP spice model is invalid?
Would someone (VAR) please check the model?

Thanks

  • Alok Tripathi

    This model will have negative VJC at about 54C and historically negative Vjc has been considered as error condition for BJTs devices in PSpice. Negative Vjc is a not valid input for BJTs (correct me if I am wrong). Other simulator like LTspice may be using (clamping to) a very low positive value in such cases and continuing with simulation. LTspice does not seem to report this also. Increase the value of VJC to somewhat large value ~0.13 (from original value of 0.102) or so to complete the simulation. With this value Vjc will remain positive at 54C. With this increased model parameter value the IC is broadly in line with value shown by Ltspice. Thus confirming that it is internally clamping the model param value. YOu may want to try this.

  • tltoth

    Thank you alokt for the response!
    You must be right with the clamping effect.
    As per datasheet the operating temperature range of this device  extends from -33 to 150.
    They also provide measurement results for 100C (see figs of datasheet)
    With VJC of 0.25 we can  reach 100C but there are other 37 temperature dependent model parameters to tune to.
    I don't believe this would be the right way...

  • Alok Tripathi

    I don't think one need to tune any other parameter. Not sure, why do you say that. However I agree with you that increasing Vjc to 0.25 may lead to difference in result at lower temperature.

  • tltoth

    I've simulated the VBE(IC) curves on Fig.5 of datasheet too by LTS and they all differed from what was specified (ca. 0.2V lower  values)
    The temperature dependency is not properly considered in case of this model.
    One would assume a device model to behave like a real device with some tolerances since this why we use the simulator for.

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