Adding a Device to LTSpiceIV

Searching around for an LM386 SPICE model turned up this useful thread.

The model has some limitations, discussed there, but seems practical. So far, the main gotcha is that the output voltage doesn’t center neatly at Vcc/2, but that’s in the nature of fine tuning.

The trick is getting the model & symbol into Linear Technology’s LTSpiceIV

Running under WINE in Xubuntu, the emulated C drive is in your home directory at

.wine/drive_c/

with the Linear Tech LTSpiceIV files tucked inside that at

.wine/drive_c/Program\ Files/LTC/LTspiceIV/

Incidentally, WINE puts the program icon in

.local/share/icons/05f1_scad3.0.xpm

It’s not clear what the prefix means, but the actual executable is scad3.exe (I think that’s historical cruft, as the new overall name is LTSpiceIV).

Copy the LM386.sub file to lib/sub and the LM386.asy file to lib/sym, then restart LTSpiceIV.

After putting the symbol in the schematic, I had to edit its attributes (other-click the symbol), make both InstName & Value visible to see them on the schematic, then move them to somewhere other than dead-center in the symbol. I can’t figure out how to make that happen automagically, as it does with other symbols. Comparing the two files to ordinary components doesn’t show anything obviously missing.

Link rot being what it is, here’s the LM386.sub file:

* lm386 subcircuit model follows:

************************************original* IC pins:     2   3   7   1   8   5   6   4
* IC pins:     1   2   3   4   5   6   7   8
*              |   |   |   |   |   |   |   |
.subckt lm386 g1  inn inp gnd out  vs byp g8
************************************original*.subckt lm386 inn inp byp  g1  g8 out  vs gnd

* input emitter-follower buffers:

q1 gnd inn 10011 ddpnp
r1 inn gnd 50k
q2 gnd inp 10012 ddpnp
r2 inp gnd 50k

* differential input stage, gain-setting
* resistors, and internal feedback resistor:

q3 10013 10011 10008 ddpnp
q4 10014 10012 g1 ddpnp
r3 vs byp 15k
r4 byp 10008 15k
r5 10008 g8 150
r6 g8 g1 1.35k
r7 g1 out 15k

* input stage current mirror:

q5 10013 10013 gnd ddnpn
q6 10014 10013 gnd ddnpn

* voltage gain stage & rolloff cap:

q7 10017 10014 gnd ddnpn
c1 10014 10017 15pf

* current mirror source for gain stage:

i1 10002 vs dc 5m
q8 10004 10002 vs ddpnp
q9 10002 10002 vs ddpnp

* Sziklai-connected push-pull output stage:

q10 10018 10017 out ddpnp
q11 10004 10004 10009 ddnpn 100
q12 10009 10009 10017 ddnpn 100
q13 vs 10004 out ddnpn 100
q14 out 10018 gnd ddnpn 100

* generic transistor models generated
* with MicroSim's PARTs utility, using
* default parameters except Bf:

.model ddnpn NPN(Is=10f Xti=3 Eg=1.11 Vaf=100
+ Bf=400 Ise=0 Ne=1.5 Ikf=0 Nk=.5 Xtb=1.5 Var=100
+ Br=1 Isc=0 Nc=2 Ikr=0 Rc=0 Cjc=2p Mjc=.3333
+ Vjc=.75 Fc=.5 Cje=5p Mje=.3333 Vje=.75 Tr=10n
+ Tf=1n Itf=1 Xtf=0 Vtf=10)

.model ddpnp PNP(Is=10f Xti=3 Eg=1.11 Vaf=100
+ Bf=200 Ise=0 Ne=1.5 Ikf=0 Nk=.5 Xtb=1.5 Var=100
+ Br=1 Isc=0 Nc=2 Ikr=0 Rc=0 Cjc=2p Mjc=.3333
+ Vjc=.75 Fc=.5 Cje=5p Mje=.3333 Vje=.75 Tr=10n
+ Tf=1n Itf=1 Xtf=0 Vtf=10)

.ends
*----------end of subcircuit model-----------

And the corresponding LM386.asy file:

Version 4
SymbolType CELL
LINE Normal -64 -63 64 0
LINE Normal -64 65 64 0
LINE Normal -64 -63 -64 65
LINE Normal -60 -48 -52 -48
LINE Normal -60 48 -52 48
LINE Normal -56 52 -56 44
LINE Normal -48 -80 -48 -55
LINE Normal -48 80 -48 57
LINE Normal -44 -68 -36 -68
LINE Normal -40 -72 -40 -64
LINE Normal -44 68 -36 68
LINE Normal -16 -39 -16 -64
LINE Normal 0 32 0 48
LINE Normal 48 -8 48 -32
SYMATTR Value LM386
SYMATTR Prefix X
SYMATTR ModelFile LM386.sub
SYMATTR Value2 LM386
SYMATTR Description Low power audio amplifier
PIN -16 -64 LEFT 8
PINATTR PinName g1
PINATTR SpiceOrder 1
PIN -64 -48 NONE 0
PINATTR PinName In-
PINATTR SpiceOrder 2
PIN -64 48 NONE 0
PINATTR PinName In+
PINATTR SpiceOrder 3
PIN -48 80 NONE 0
PINATTR PinName V-
PINATTR SpiceOrder 4
PIN 64 0 NONE 0
PINATTR PinName OUT
PINATTR SpiceOrder 5
PIN -48 -80 NONE 0
PINATTR PinName V+
PINATTR SpiceOrder 6
PIN 0 48 LEFT 8
PINATTR PinName bp
PINATTR SpiceOrder 7
PIN 48 -32 LEFT 8
PINATTR PinName g8
PINATTR SpiceOrder 8

Props to Roff, who actually created those files…

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