Crossreference for a AD542KH?

You most likely won't find one in that package how ever, if you google PRECISION op-amps., you'll fine many that actually have much better spec's than what you're looking for and you can simply adapt one on the board, if this is just a repair problem..

We have done this many times, replacing those older types of IC's with newer types that have far lower offsets and noise figures. It usually ends up with a better overall operating device.

P.S. If this IC is part of a balanced circuit (i.e., kelvin bridge), you'll need to replace both.

Hi Jamie,

That wouldn't be a problem. But I'm not sure what I should replace it

*with* unfortunately. Never was any good at picking a good sub. :( It is located in a HP 3478A 5.5 digit DMM, location U101, on the main board in the current source circuit. Warning: it is 10.4MB if anybody is on dial-up.

Nope, it's not.

Thanks.

INA121PA

Try that, Its found at mouser.com, the offset voltage isn't as good as the original but it's very close. I would say the important part of it's operation that you need actually out spec's the original.

[...]

OK, I'll give that one a try. Should I leave pins 1 and 8 disconnected for gain of 1? The original device didn't have these pins...

Thanks again.

I'd be careful about that. AD542 is an OPamp. INA121 is an INamp. They are very different in function.

Have you tried crossing it on ADI's web site? I'm sure they have something comparable or better in the present catalog, though as another poster has said, possibly not in the metal can package.

[...]

Hi Stephan,

Yes, I did try to see if their web page would offer up a sub, but it offers the AD544 and AD547 which are also obsolete. Thanks though.

What voltage do you need? If the supply is smaller then 16 Volt, the AD8638 might be an option.

--
Uwe Bonnes                bon@elektron.ikp.physik.tu-darmstadt.de

Institut fuer Kernphysik  Schlossgartenstrasse 9  64289 Darmstadt
--------- Tel. 06151 162516 -------- Fax. 06151 164321 ----------

cal=3Den

A

But, what are the power supplies connected to? A true drop-in replacement if it takes +/-18V is going to be hard; if your power supply is +/- 5V it gets easier. Using a 'cross reference' will not find options that meet only SOME of the specs, even if that would suit your application nicely.

You need to set the gain at max. use R around the 5K region.

There is an issue here how ever, I don't know if you have +/- supply with reference to common? I can only assume that you do, in which case, the REF pin needs to be on the common, not the (-) rail.

After you have done that, the device should behave like your original.

--
  I\'ve just did another look at your PDF file of your meter and the 
op-amp you\'re using.

  I do think a  AD743 would be more particle for you even though the 
input current is alittle higher. The data sheet does
not give a warm up time and drift how ever, in your application it may 
not matter.

   If you want to stick with older technology that is still being used 
out there for the Bifet family..

   The LF355/6/7, if you employ the balance circuit they show, it\'ll get 
you to the input offset equal to what you need how ever, you may not 
even need to do this. It\'s also possible you may still find in some old
stock the can packages which are pin for pin compatible.

   It\'s just a matter of how exact you want the chip to be like the 
original when it comes to stability in settling time and drift. I really
don\'t think you\'ll have issues for your needs.


Personally, I would experiment with the LF355/6/7 family and see how it 
does. It don\'t cost that much so it\'s not like you\'re losing your
shirt tail.

The supply in this circuit is +/- 15V. Thanks.

Do you have room to fit a plastic DIP with the proper adapter or wiring? This will open up a much larger universe of potential replacement parts. It may well be that the metal can package is obsolete, but not others (I'll check when I get to work). As this is an instrument you probably don't need the wide temperature range, but simply the specs of the K version. (K is electrical grade, H is metal-can package).

It's possible, though, that the metal can provides some shielding. You won't get this with a plastic pack.

How many do you need. Perhaps I can find one in a drawer somewhere. Send me an email, but remove the upper-case food item first!

I have a couple of AD542KH sitting on my desk right now. They are datecode 8517, but have never been used as far as I can tell, and have always been stored in a controlled (lab) environment. Part of the secret stash...

Where shall I send them? Send me an email. To do so, you will need to remove the uppercase letters from the indicated posting address. Hint - there are three such.

Steve

Hello Steve,

Check your email, and thank you very much!

Jay

Nice guy you are :)

Those AD542s were never going to get used, the last time we used them in a test fixture or breadboard was over 20 years ago. I'm glad they could be of use to someone.

Maybe some day you'll be able to do the same for me or someone else.

Well, thanks for the offer, we too have a collection of the older CAN type packages we bought out a few years ago to keep our aging RDI equipment working.

Our facility still has in operation the very first, ever built, irradiation unit for x-linking of ployrads etc.. This unit still is using much of it's original electronics. The chemical engineering of the first X linking compounds were also developed at the facility..

Of course, the world has grown and every one and their brother has this process now :)