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ODD Spice! (LT1213 model error?)

Please can someone tell me if they can replicate this (in a default install of LTspice)?

It's a differential amp set to gain of 0.25 (though unity or other shows same effect). It drives the output hard to the supply rail and stays there! If you replace the LT1213 model with the LT1215 (faster slew rate, twice supply current but otherwise very similar IC), you get the expected standard differential amplifier behaviour.

WHY? :) I've looked to see if there's anything in the data sheet to indicate why, and there isn't, they really look like they should both behave very similarly here.

I've looked at LT's site to see if there's a later (or fixed) model but it's the same, and LT1214 is also the same as 1213 with same error.

Copy below, save as LT1213 Test.asc...

Version 4 SHEET 1 880 680 WIRE 192 128 176 128 WIRE 240 160 224 160 WIRE 96 176 -48 176 WIRE 176 176 176 128 WIRE 192 176 176 176 WIRE -112 192 -128 192 WIRE 272 192 272 128 WIRE 272 192 256 192 WIRE -128 208 -128 192 WIRE -48 208 -48 176 WIRE 96 208 32 208 WIRE 192 208 176 208 WIRE 176 224 176 208 WIRE 224 272 224 224 WIRE 256 272 224 272 WIRE 256 288 256 272 WIRE -128 304 -128 288 WIRE -48 304 -48 288 WIRE -48 304 -128 304 WIRE 32 304 32 288 WIRE 32 304 -48 304 WIRE 176 304 32 304 WIRE 224 304 224 272 WIRE 224 304 176 304 FLAG -112 192 12V FLAG 240 160 12V FLAG 256 288 0 SYMBOL voltage 32 192 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value 5V SYMBOL voltage -48 192 R0 WINDOW 3 -2 -39 Left 0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V2 SYMATTR Value PULSE(0 5V 0 0 0 0.49µ 1µ) SYMBOL res 176 144 R270 WINDOW 0 12 82 VTop 0 WINDOW 3 6 56 VBottom 0 SYMATTR InstName R1 SYMATTR Value 7.5K SYMBOL res 80 192 R270 WINDOW 0 12 83 VTop 0 WINDOW 3 8 56 VBottom 0 SYMATTR InstName R2 SYMATTR Value 30K SYMBOL res 80 224 R270 WINDOW 0 12 83 VTop 0 WINDOW 3 9 56 VBottom 0 SYMATTR InstName R3 SYMATTR Value 30K SYMBOL res 160 208 R0 WINDOW 0 17 26 Left 0 WINDOW 3 19 79 Left 0 SYMATTR InstName R4 SYMATTR Value 7.5K SYMBOL voltage -128 192 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V3 SYMATTR Value 12V SYMBOL Opamps\\\\LT1213 224 128 R0 WINDOW 0 -19 64 Left 0 SYMATTR InstName U1 TEXT -162 130 Left 0 !.tran 1m startup

Reply to
Lostgallifreyan
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Ok, I found where the problem happens but I don't understand why, yet.

If you remove the 'startup' from the spice directive it works, so it looks like it latches up if it gets a signal on it before a power supply.

Anyone know why though? I'm not sure if anything in the data sheets make it clear why the LT1215 doesn't have this problem while the LT1213 does. Also, does this difference indicate a weakness in the models, or a strength? It looks like fine detail, but I don't know if it's correct. For one thing, probing the non-inverting input in the unedited version I posted shows a very unlikely 40 volts which doesn't seem right, model or no model!

I'll stick with the LT1215 anyway though, I want that fast slew rate.

Reply to
Lostgallifreyan

"Lostgallifreyan" schrieb im Newsbeitrag news:Xns9C5B34CEBC91Czoodlewurdle@216.196.109.145...

Hello,

This behavior isn't with the real device. It's only a convergence issue if the "startup" option is used. You can either don't use the "startup" with this circuit or you could defeat gmin-stepping.

.options gminsteps=0

This option will give you the correct result even when using "startup" in the .TRAN-analysis.

Best regards, Helmut

formatting link

The test circuit "test.asc" is below. If the last line is splitted, please correct it with a text editor.

Version 4 SHEET 1 880 680 WIRE 48 96 -96 96 WIRE 80 96 48 96 WIRE 208 96 160 96 WIRE 272 96 208 96 WIRE 416 96 352 96 WIRE 352 160 320 160 WIRE -208 176 -224 176 WIRE 320 192 320 160 WIRE -224 208 -224 176 WIRE -96 208 -96 96 WIRE 208 208 208 96 WIRE 288 208 208 208 WIRE 416 224 416 96 WIRE 416 224 352 224 WIRE 464 224 416 224 WIRE 80 240 16 240 WIRE 176 240 160 240 WIRE 208 240 176 240 WIRE 288 240 208 240 WIRE 16 256 16 240 WIRE 208 256 208 240 WIRE -224 320 -224 288 WIRE -96 352 -96 288 WIRE 16 352 16 336 WIRE 16 352 -96 352 WIRE 208 352 208 336 WIRE 208 352 16 352 WIRE 320 352 320 256 WIRE 320 352 208 352 WIRE 320 384 320 352 FLAG -208 176 12V FLAG 352 160 12V FLAG 320 384 0 FLAG -224 320 0 FLAG 464 224 out FLAG 48 96 in1 FLAG 176 240 in2 SYMBOL voltage 16 240 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 WINDOW 0 38 35 Left 0 WINDOW 3 34 86 Left 0 SYMATTR InstName V1 SYMATTR Value 5V SYMBOL voltage -96 192 R0 WINDOW 3 -14 183 Left 0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR Value PULSE(0 5V 0 0 0 0.49µ 1µ) SYMATTR InstName V2 SYMBOL res 256 112 R270 WINDOW 0 40 56 VTop 0 WINDOW 3 -3 53 VBottom 0 SYMATTR InstName R1 SYMATTR Value 7.5K SYMBOL res 64 112 R270 WINDOW 0 38 53 VTop 0 WINDOW 3 -2 56 VBottom 0 SYMATTR InstName R2 SYMATTR Value 30K SYMBOL res 64 256 R270 WINDOW 0 39 52 VTop 0 WINDOW 3 -6 52 VBottom 0 SYMATTR InstName R3 SYMATTR Value 30k SYMBOL res 192 240 R0 WINDOW 0 46 30 Left 0 WINDOW 3 38 70 Left 0 SYMATTR InstName R4 SYMATTR Value 7.5K SYMBOL voltage -224 192 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 WINDOW 0 34 38 Left 0 SYMATTR InstName V3 SYMATTR Value 12V SYMBOL Opamps\\\\LT1213 320 160 R0 WINDOW 0 -19 64 Left 0 SYMATTR InstName U1 TEXT -224 48 Left 0 !.tran 1m startup TEXT -224 16 Left 0 !.options gminsteps=0 TEXT -224 -16 Left 0 ;"gminsteps=0" is only required with the LT1213 if "startup" is used

Reply to
Helmut Sennewald

"Helmut Sennewald" wrote in news:h539e6$qck$00$ snipped-for-privacy@news.t-online.com:

Great answer, works perfectly. I noticed that extra spice directive on the 'test fixture' for the LT1213 but I didn't realise it was for something beyond the filtering circuit behaviour for that circuit so I didn't yet try it..

I found some cheap ones so I'll buy them anyway now I know they won't latch up. Or if they do, it won't hurt much finding out. :)

I just bit the bullet of having to sign up to Yahoo, just so I could join that one...

Reply to
Lostgallifreyan

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