This was empiricallyįound to be a good approximation for power MOSFETS if the gate-source Gate-source capacitance is taken as constant. Length and width default to one so that transconductance can beĭirectly specified without scaling. Model is the same as a level 1 monolithic MOSFET except that the Reliability of convergence, and simplicity of writing models. That encapsulates this behavior in the interest of compute speed, Traditionally, elaborate subcircuits have been used to duplicate theīehavior of a power MOSFET. Vgd is positive, the die is conducting and Cgd is physically based onĪ capacitor with the thickness of the gate oxide. Is fairly low due to the thickness of the non-conducting die. Physically based a capacitor with the gate as one electrode and theĭrain on the back of the die as the other electrode. In a VDMOS transistor, Cgd abruptly changesĪbout zero gate-drain voltage(Vgd). Non-linearity cannot be modeled with the simple graded capacitances of
In particular, (i) the body diode of a VDMOS transistor isĬonnected differently to the external terminals than the substrateĭiode of a monolithic MOSFET and (ii) the gate-drain capacitance(Cgd) That is qualitatively different than the above monolithic MOSFET Popularly used in board level switch mode power supplies has behavior The discrete vertical double diffused MOSFET transistor(VDMOS)
The most relevant information is duplicated below: You can find more info in the LTspice Help page for MOSFETs. This builds upon a LEVEL=1 monolithic MOSFET, but changes a few things while keeping the simulation speed high.
However, LTspice (due to its focus for simulating switch-mode power supplies) created its own proprietary structure called the VDMOS. Everything else in there are additional components around the MOSFET to assist in modeling it accurately. That is what you see in the 2N7000 subcircuit provided by OnSemi, where the. So, in order to accurately model those, manufacturers needed to create more complex subcircuits around a base monolithic MOSFET. The built-in SPICE MOSFET structures are for lateral monolithic (i.e.
This is actually quite tricky, due to (1) how SPICE models in general are not typically created from datasheet parameters, and (2) how discrete power MOSFETs are modeled in the first place.
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