Re: OPA349 spice model acting weird

"Tom (at tomsweb.net)" <tomtorfs@xxxxxxxxxxxxxxxx> schrieb im Newsbeitrag
news:1120485223.769825.269940@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> Everyone,
>
> I am trying to simulate a circuit (using LTSpice) with a OPA349 from
> Burr-Brown: 1 microamp Iq, 70kHz GBW, CMOS rail-rail I/O, 1.8V-5.5
> opamp. According to the data***
> (http://focus.ti.com/lit/ds/symlink/opa349.pdf) this one can drive 8mA
> without problems.
>
> The OPA349 appears to misbehave in my circuit simulations, so I created
> a simple test circuit consisting of a simple unity gain inverter with 1
> Meg input, feedback and load resistors.
>
> With a 1 MEG load the opamp seems to go out of closed-loop at Vin<0.8V
> with a 2.2V single supply, whereas the output is supposed to swing to
> 350mV from the rails with a 10K load, and the input CM range extends
> 200mV past either rail. If I load the opamp with 10 MEG or more it
> seems to work. At 100K load or less the simulations become total crap.
> Changing the feedback resistors to higher or lower values does not
> improve things either.
>
> Is this a bug in the model? Or am I missing something? I don't have a
> physical chip to test it on right now, but since the opamp can drive
> 8mA (and is specced for a rail-to-rail output at 10K load) I really
> don't think this is how the real hardware should behave!
>

Hello Tom,
I tried the model with LTspice and see the same problem as you
have described. I recommend you write a letter to AD.

Best regards,
Helmut



> Substituting a different opamp model (e.g. OPA336) works as expected.
> Any suggestions? Below spice netlist, opamp model, LTSpice schematic
> and LTSpice symbol for OPA349...
>
> Spice netlist:
> * d:\tom\spice\opa349test.asc
> XU1 V+ V- VDD 0 VO opa349 opa349
> R1 V- Vi 1MEG
> R2 VO V- 1MEG
> RL VO 0 1MEG
> V1 V+ 0 1.2V
> V2 Vi 0 PULSE(0 2.2 0 500ms 500ms 0ms 1s)
> V3 VDD 0 2.2V
> .tran 1s
> .include opa349.mod
> .backanno
> .end
>
> OPA349 model (from
> http://focus.ti.com/docs/prod/folders/print/opa349.html)
> *
> * OPA349 operational amplifier "macromodel" subcircuit
> * REV A created using Parts release 8.0 on 11/23/99 at 17:01 by Vadim
> Ivanov
> * REV B Revised 25 August 2000 by Vadim Ivanov
> * Parts is a MicroSim product.
> *
> * connections: non-inverting input
> * | inverting input
> * | | positive power supply
> * | | | negative power supply
> * | | | | output
> * | | | | |
> .subckt OPA349 + - V+ V- OUT
> *
> *
>
> * INPUT STAGE
>
> *
>
> iin V+ 5 200n
>
> m7 550 vswitch 5 5 pix l=.6u w=20u m=2
>
> m8 550 550 V- V- nix l=4u w=4u m=1
>
> m9 553a 550 V- V- nix l=4u w=4u m=1
>
> m9c 66 nvsat 553a V- nix l=.6u w=4u m=1
>
> Vpvsat V+ vswitch DC 1.3
>
> Vnvsat nvsat V- DC 1.37
>
> iin1 + 98 .2p
>
> iin2 - 98 .2p
>
> d3 5 V+ dx
>
> d4 V- 66 dx
>
> d5 - V+ dx
>
> d6 + V+ dx
>
> d7 V- - dx
>
> d8 V- + dx
>
> m1 33 - 66 V- nix l=5u w=5u m=1
>
> m2 4 + 66 V- nix l=5u w=5u m=1
>
> m3 8 - 5 5 pix l=5u w=5u m=1
>
> m4 9 + 5 5 pix l=5u w=5u m=1
>
> r1 V+ 33 .1meg
>
> r2 V+ 4 .1meg
>
> r3 8 V- .1meg
>
> r4 9 V- .1meg
>
>
> *
>
> * GAIN STAGE
>
> *
>
> eref 98 V- poly(2) V+ V- V- V- 0 0.5 0.5
>
> g1 98 21 poly(2) 4 33 9 8 0 2.3u 2.3u
>
> rg 21 98 2e10
>
> cc 21 OUT 2p
>
> d1 21 22 dx
>
> d2 23 21 dx
>
> v1 V+ 22 1.37
>
> v2 23 V- 1.37
>
> *
>
> * COMMON MODE GAIN STAGE
>
> *
>
> *ecm 24 98 poly(2) + 98 - 98 0 0.5 0.5
>
> *r5 24 25 1e6
>
> *r6 25 98 10k
>
> *c1 24 25 0.75p
>
> *
>
> * OUTPUT STAGE
>
> *
>
> * isy V+ V- 450.4u
>
> * gsy V+ V- poly(1) V+ V- -3.334e-4 6.667e-5
>
> ep V+ 39 poly(1) 98 21 0.7515 .01
>
> en 38 V- poly(1) 21 98 0.7515 .01
>
> vh OUT 6h DC 1e-2
>
> vl 6l OUT DC 1e-2
>
> m113 6h 39 V+ V+ pox l=.6u w=1500u
>
> m114 6l 38 V- V- nox l=.6u w=1500u
>
> c15 OUT 39 3p
>
> c16 OUT 38 3p
>
> .model dx d(rs=1 cjo=0.1p)
>
> .model nix nmos(vto=0.75 kp=205.5u rd=1 rs=1 rg=1 rb=1 cgso=4e-9
>
> +cgdo=4e-9 cgbo=16.667e-9 cbs=2.34e-13 cbd=2.34e-13)
>
> .model nox nmos(vto=0.75 kp=195u rd=.5 rs=.5 rg=1 rb=1 cgso=66.667e-12
>
> +cgdo=66.667e-12 cgbo=125e-9 cbs=2.34e-13 cbd=2.34e-13)
>
> .model pix pmos(vto=-0.75 kp=205.5u rd=1 rs=1 rg=1 rb=1 cgso=4e-9
>
> +cgdo=4e-9 cgbo=16.667e-9 cbs=2.34e-13 cbd=2.34e-13)
>
> .model pox pmos(vto=-0.75 kp=195u rd=.5 rs=.5 rg=1 rb=1 cgso=66.667e-12
>
> +cgdo=66.667e-12 cgbo=125e-9 cbs=2.34e-13 cbd=2.34e-13)
>
> .ENDS OPA349
> *
> *
>
> LTSpice schematic:
> Version 4
> *** 1 880 680
> WIRE -240 256 -240 208
> WIRE -160 208 -240 208
> WIRE -112 208 -160 208
> WIRE -64 288 -64 240
> WIRE -64 304 -64 288
> WIRE 0 208 -32 208
> WIRE 0 208 0 128
> WIRE 16 208 0 208
> WIRE 16 240 -64 240
> WIRE 32 128 0 128
> WIRE 48 288 48 256
> WIRE 144 128 112 128
> WIRE 144 176 144 128
> WIRE 144 224 80 224
> WIRE 144 224 144 176
> WIRE 192 176 144 176
> WIRE 192 208 192 176
> WIRE 192 304 192 288
> FLAG 48 288 0
> FLAG 48 192 VDD
> FLAG 144 176 VO
> FLAG 192 304 0
> FLAG -160 208 Vi
> FLAG -64 288 V+
> FLAG 0 208 V-
> FLAG 272 48 VDD
> FLAG 272 128 0
> FLAG -64 384 0
> FLAG -240 336 0
> SYMBOL opa349 48 160 R0
> SYMATTR InstName U1
> SYMBOL res -16 192 R90
> WINDOW 0 -3 94 VBottom 0
> WINDOW 3 -27 39 VTop 0
> SYMATTR InstName R1
> SYMATTR Value 10MEG
> SYMBOL res 128 112 R90
> WINDOW 0 -4 87 VBottom 0
> WINDOW 3 -31 30 VTop 0
> SYMATTR InstName R2
> SYMATTR Value 5MEG
> SYMBOL res 176 192 R0
> SYMATTR InstName RL
> SYMATTR Value 100K
> SYMBOL voltage -64 288 R0
> SYMATTR InstName V1
> SYMATTR Value 1.2V
> SYMBOL voltage -240 240 R0
> WINDOW 123 0 0 Left 0
> WINDOW 39 0 0 Left 0
> WINDOW 0 -76 25 Left 0
> WINDOW 3 -477 74 Left 0
> SYMATTR InstName V2
> SYMATTR Value PULSE(0 2.2 0 500ms 500ms 0ms 1s)
> SYMBOL voltage 272 32 R0
> SYMATTR InstName V3
> SYMATTR Value 2.2V
> TEXT -282 490 Left 0 !.tran 1s
> TEXT -280 464 Left 0 !.include opa349.mod
>
> OPA349 LTSpice symbol:
> Version 4
> SymbolType CELL
> LINE Normal -32 32 32 64
> LINE Normal -32 96 32 64
> LINE Normal -32 32 -32 96
> LINE Normal -28 48 -20 48
> LINE Normal -28 80 -20 80
> LINE Normal -24 84 -24 76
> LINE Normal 0 32 0 48
> LINE Normal 0 96 0 80
> LINE Normal 4 44 12 44
> LINE Normal 8 40 8 48
> LINE Normal 4 84 12 84
> WINDOW 0 16 32 Left 0
> WINDOW 3 16 96 Left 0
> SYMATTR Value opa349
> SYMATTR Prefix X
> SYMATTR SpiceModel opa349
> SYMATTR Description Precision Operational Amplifier
> PIN -32 80 NONE 0
> PINATTR PinName In+
> PINATTR SpiceOrder 1
> PIN -32 48 NONE 0
> PINATTR PinName In-
> PINATTR SpiceOrder 2
> PIN 0 32 NONE 0
> PINATTR PinName V+
> PINATTR SpiceOrder 3
> PIN 0 96 NONE 0
> PINATTR PinName V-
> PINATTR SpiceOrder 4
> PIN 32 64 NONE 0
> PINATTR PinName OUT
> PINATTR SpiceOrder 5
>


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