Problem simulating MOSFET Idss in LTSPICE

Discussion in 'The Projects Forum' started by misterbevis, Oct 17, 2011.

  1. misterbevis

    Thread Starter New Member

    Jun 24, 2011
    2
    0
    Hi,

    I'm trying to simulate the behavior of a PMOS FET (BSH201) using the manufacturer's SPICE model. The datasheet states that the Idss (zero gate voltage drain current) is typically 50nA with Vds = -48V. However, when I run the simulation, the drain current is around 75uA (over 1000x times higher).

    I also tried it with an IRLML6401 (at a lower voltage) and the drain current was also several orders of magnitude too high.

    I'm running it with default settings in LTSPICE.

    Any ideas what's causing this, or what I can do to solve it?

    Many thanks
     
  2. crutschow

    Expert

    Mar 14, 2008
    13,019
    3,235
    I don't have models for your transistors but I tried a couple that are in LTspice and they both gave values much less than a nA, so it appears to be your models.

    Try doing a DC Operating Point (.OP), instead of a transient analysis.
     
  3. misterbevis

    Thread Starter New Member

    Jun 24, 2011
    2
    0
    crutschow,

    Thanks for looking into that for me. With the DC Operating Point analysis it gives the same Idss (approx 75uA), so it looks like it must be the model.

    The model I'm using, given by the manufacturer, is:

    .SUBCKT BSH201 1 2 3
    * 1=drain 2=gate 3=source
    Cgs 6 3 159e-12
    Cgd1 6 4 148e-12
    Cgd2 1 4 5e-12
    M1 5 6 3 3 MOST1
    M2 4 6 5 3 MOST2
    D1 1 3 Dbody
    Rd 5 1 Rtemp 1.6
    Rg 2 6 250
    .MODEL MOST1 PMOS(Level=3 W=0.1 L=0.3e-6 Vto=-1.91 Kp=9.27e-7
    + Rs=0 Rd=0 Uo=650 Vmax=0 Xj=5e-7 Kappa=0.08
    + Eta=2e-5 Tpg=-1 Is=0 Ld=0 Wd=0 Cgso=0 Cgdo=0
    + Cgbo=0 Nfs=3e12 Delta=0.1 Theta=0)
    .MODEL MOST2 PMOS(Level=3 W=0.1 L=0.3e-6 Vto=1.19 Kp=9.27e-7
    + Rs=1000 Rd=1000 Uo=650 Vmax=0 Xj=5e-7 Kappa=0.08
    + Eta=2e-5 Tpg=-1 Is=0 Ld=0 Wd=0 Cgso=0 Cgdo=0
    + Cgbo=0 Nfs=0 Delta=0.1 Theta=0)
    .MODEL Dbody D(Is=1e-14 N=0.8 Rs=0.7 Ikf=1e3 Cjo=0 M=0.3 Vj=0.3
    + Bv=60 Ibv=10e-6 Tt=70e-9 Fc=0.5)
    .MODEL Rtemp RES(TC1=5.225e-3 TC2=1.7e-5)
    .ENDS

    Out of interest, which devices did you use for your simulation? Was it just the standard 'PMOS' devices? Obviously the device I'm using is a power MOSFET and perhaps the models aren't intended to model the Idss accurately.

    Best regards
     
  4. crutschow

    Expert

    Mar 14, 2008
    13,019
    3,235
    Using a IRF9Z24S_L from the PMOS library I get a current of Id current of
    -1.72221e-011, for example.
     
Loading...