# Thread: Problem with BSZ42DN25NS3 PSPICE model

1. ## Problem with BSZ42DN25NS3 PSPICE model

The top-level model for this MOSFET calls another subcircuit: S3_250_n_var.

The S3_250_n_var subcircuit contains this line: .PARAM bm={c/((1/gmin-Rs)**2*Inn*a*(T0/Tref)**nmu3)}

This subcircuit won't simulate because the model sets both gmin and Rs to 1, which causes the expression to evaluate to "INF":

.SUBCKT S3_250_n_var dd g s0 Tj PARAMS: a=1 dVth=0 dR=0 dgfs=0 Inn=1 Unn=1 Rmax=1 gmin=1 Rs=1 Rp=1 dC=0 Rm=1u heat=0

Has someone successfully used this model? What should be the values for gmin and Rs?

2. Parameter RS and gmin are set as .PARAM Rs=564u and gmin=3 in .SUBCKT BSZ42DN25NS3

.SUBCKT BSZ42DN25NS3 drain gate source Tj Tcase PARAMS: dVth=0 dRdson=0 dgfs=0 dC=0 Zthtype=0 Ls=1n Ld=1n Lg=3n

.PARAM Rs=564u Rg=2 Rd=50u Rm=250u
.PARAM Inn=2.5 Unn=10 Rmax=427m gmin=3
.PARAM RRf=497m Rrbond=11m Rtb=5 g2=947m
.PARAM act=1.274

.FUNC Pb(I,dT,Rb) {Rb/(2*Rtb)*(I-limit(dT/(max(I,1n)*Rb)+RRf*I*g2,0,I))**2}

X1 d1 g s Tj S3_250_n_var PARAMS: a={act} dVth={dVth} dR={dRdson} dgfs={dgfs} Inn={Inn} Unn={Unn}
+Rmax={Rmax} gmin={gmin} Rs={Rs} Rp={Rd} dC={dC} Rm={Rm}

The simulation works fine.

3. My version of SPICE simulator must not be passing the top-level values down to the lower-level subcircuit. Changing the values in the lower-level subcircuit allows the simulation to run properly.

Thanks.

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