Spice problem

I have LTspice v4.19s, which I think is the latest.

Searching the directory structure, I find neither an assembly (.ASY) or a model (.SUB, .LIB, or .MOD) for LT1028N. ...Jim Thompson

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Checked sync release, now up to 4.19u, no LT1028N. ...Jim Thompson

It's in this library....

From the date of the library... is it an obsolete part? ...Jim Thompson

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where have you found LT1028N? I can't find it int the latest version, and when looking at the linear site it doesn't even exist

-Lasse

Found it in this old library...

It's not in the latest version of ASY symbols. ...Jim Thompson

And the symbol here...

...Jim Thompson

LT1028N symbol calls LTC.lib, but LT1028N isn't in there, only LT1028.

It's not in any of the other .lib files, either, according to grep.

Looks like they slipped up.

Where did you find an LT1028N symbol? My v4.19u doesn't have it.

Methinks it's been dropped. Haven't found a datasheet. ...Jim Thompson

And searching the Linear website for LT1028N only returns LT1028. ...Jim Thompson

-- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at

Found an old library file in my backup directory, with an LT1028 subcircuit. Looks like it's obsolete. D'you want the subcircuit?

Probably the same way as me. I never sync versions, but install over the top. That way it doesn't screw up your existing, customized files, and backs up the ones that it does overwrite.

I posted a link earlier.

Digging into the fine print of the LT1028 data sheet, an overcompensation pin (5 on the 8-pin packages), plus a couple graphs and some vague comments. Also two pins for VOS adjust.

Maybe _all_ LT1028's have the over-comp available? ...Jim Thompson

I meant to say that I have the original N-suffix subcircuit available.

LT1028N Comp is pin 6

• input protection DIP1 1 114 DX DIP2 114 2 DX DIP3 2 115 DX DIP4 115 1 DX
• input stage CIN 1 2 5e-12 GRIN 1 2 1 2 4.9568e-5 Q1 11 2 13 Q1 Q2 12 111 14 Q2 GRC1 3 11 3 11 0.00087653 GRC2 3 12 3 12 0.00087653

• add 3dB gain GRE1 10 13 10 13 -0.12667 GRE2 10 14 10 14 -0.12667 C1 11 12 2.9063e-12 IEE 10 4 DC 0.0017531 D1 4 10 DX GA 60 99 11 12 0.00087653
• noise sources FRI1 99 1 VRI1 1 VRI1 101 0 DC 0 RRI1 101 0 16823 FRI2 99 2 VRI2 1 VRI2 201 0 DC 0 RRI2 201 0 16823 GR 99 60 605 606 0.78354 IR1 0 605 DC 1 IR2 0 606 DC 1 DR1 605 0 DR DR2 606 0 DR
• common mode rejection GCM1 99 20 POLY(2) 1 99 2 99 0 0.0005 0.0005 RCM1 21 99 1000 RCM2 20 99 1000000 LCM 20 21 0.22736 ECM 111 1 20 99 5.0119e-7
• frequency shaper RP1 601 99 2381 CP1 60 601 1.2855e-11 RP11 60 99 10000 GP1 99 61 60 99 0.0001 RP2 61 99 10000 CP2 61 99 7.9577e-13 GP2 99 62 61 99 0.0001 RP3 621 99 13514 LP3 62 621 0.0004136 RP33 62 99 38462 GP3 99 6 62 99 0.0001
• output stage R2 6 99 1000 C2 6 7 9.9e-11 GB 7 99 6 99 12605 R01 7 99 51.017 R02 7 50 0.1 R03 50 5 28.883 R04 5 99 1.0000e+012 VC 53 50 DC 3.1 VE 54 50 DC -3.1 DC1 53 55 DX DC2 55 56 DX DE1 57 54 DX DE2 58 57 DX GVC1 3 56 3 56 1.0E-4 GVE1 4 58 4 58 1.0E-4 GVC2 3 55 3 55 1.0E-5 GVE2 4 57 4 57 1.0E-5 GVLP 99 60 56 3 1 GVLN 99 60 58 4 1 ECLP 91 0 7 50 250 ECLN 92 0 7 50 250 DCLP 91 90 DX DCLN 90 92 DX VLIM 90 0 DC 0 FB 7 99 VLIM 437.2
• supply characteristic EGND 99 0 POLY(2) 3 0 4 0 0 0.5 0.5 DSUB 4 3 DX IP 3 4 DC 0.0058469 GV 31 0 7 50 10 DP1 3 31 DX DP2 33 4 DX RGV 32 33 10.0 EGV 31 32 POLY(1) 3 4 -0.8 1.0 .MODEL DX D IS=8e-16 RS=0 XTI=0 .MODEL Q1 NPN IS=9.9962e-16 BF=28275.3 XTB=1.1751
• XTI=2.9998 KF=1.6891e-14 .MODEL Q2 NPN IS=1.0004e-15 BF=58435.6 XTB=1.0246
• XTI=3.0002 KF=1.6891e-14 .MODEL DR D IS=8e-16 KF=2.874e-18 RS=0 XTI=0 .ENDS LT1028N

Mike tells me that the 1028N model wasn't accurate, so he deleted it. Part of the 1028N stuff was apparently still in my lib files, and in the opamp selection list. He suggested a resync, which didn't change things, so I did a full remove/reinstall, which *did* delete it.

The new 1028 model is supposed to be better, but it doesn't bring out the overcomp pin, which the 1028N model did, and I'd like to use.

I'd like to use the 1028 as a follower, and it's not stable that way. I figured I could tune the overcomp cap to make it stable and to make it really gain/phase flat to to a MHz or two, but I can't sim that now.

Most opamps, as followers, have a small gain peak before they roll off. Adding a RC lowpass downstream can tune that, at the expense of output impedance and one more part.

Life sucks.

The 1028N model was a version of the 1028 model that brought out the overcomp pin. All physical LT1028s have that pin, but Spice doesn't support it any more.

The LT1028 isn't the best option for a low noise op amp these days, except for special cases. It has a nasty noise and compensation whoopdedoo around 300 kHz that the data sheet doesn't come clean about (at least the one I have doesn't). How about a nice well behaved ADA4898 or ADA4899?

Cheers

Phil Hobbs

OK, thanks, I'll look at those.

Comparing the datasheet, and the models, I find that the pinouts don't match, output on the wrong pin (5), should be 6.

Small signal transient response of the LT1028 model shows far too much overshoot, compared with datasheet waveform photograph, under stated conditions, and looks much more like LT1128.

Both using 10ns risetime test pulse.

I assume that the datasheet is authoritative. The real device looks much nicer than the model predicts.

Not what we've come to expect from LTC. At least they came clean.