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opamp selector

Discussion in 'Electronic Design' started by colin, Sep 18, 2006.

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  1. colin

    colin Guest

    Is there a good op amp selector guide anywhere where you can see all the
    parameters you want and the price from all the suppliers ?

    It always seems to consume so much time looking for the opamp wich has the
    best specs for the best price,
    I use Farnell mostly, but if I enter every parameter I need it usualy turns
    up nothing,
    so I spend ages looking at datasheets.

    For instance I need a better op amp for my PLL loop, it just drives a 30v
    varactor based vco with usual filter,
    at the moment im using a lm358, I have loads of them as theyr quite cheap
    and will do for many situations,
    however I need to increase the loop bandwidth wich is limited by the 1mhz
    gbw of the op amp.

    requirments :-single supply 30v, low ICC, at least 25mhz gbw, low IIB,
    short circuit protected, able to drive 100R+1nf series load
    good PSRR, moderate noise/offset etc.
    no nasty surprises such as diodes accros the inputs etc..
    idealy dual amp in soic8,

    It would be good to find one thats good enough to use in as many places as
    possible and cheap enough to buy in bulk.

    Colin =^.^=
     
  2. feebo

    feebo Guest

    I always used Towers... I haven't had my hands on this for years now
    but it was pretty much what you ask - a telephone directory, paramters
    across the top (both pages) chips down the side - made it realy easy
    to select a piece... sometimes you'd find just what you were after and
    it'd be sunnik like $100 10+ eek!
     
  3. Fred Bartoli

    Fred Bartoli Guest

    colin a écrit :
    Cheap enough to buy by the truck load? Well, it depends, but the
    OPA228/2228 will fit the bill on all your other criteria.
     
  4. colin

    colin Guest

    "Fred Bartoli"
    Yes thanks that looks quite good, 1 quid from Farnell, only problem is its
    minimum gain of 5, the opa227 is unity gain stable but only 8mhz,
    from the same table there is 180mhz device but input bias is 2ua wich is
    quite high.

    Colin =^.^=
     
  5. Joerg

    Joerg Guest

    Hello Colin,

    Digikey has just about the best search engine of all of them. Just key
    in "opamp", then narrow down the search parameters to what you want.
    Hold the shift key for whole ranges.

    Unfortunately even the Digikey search has one serious flaw. It does not
    let you sort by price. But once you have it narrowed down to a few pages
    it's easy to scoot the pane to the right and scroll through the prices.

    This will also let you avoid stuff that's low in stock or out.
     
  6. colin

    colin Guest

    doesnt seem that good to me or am I missing something ?
    doesnt let me specify GBW of >=30mhz for example.
    doesnt even tell me what the GBW is unless I select a part and go look up
    the data sheet or catalogue page.
    I can select high speed or wideband but what do they call high speed ?

    RS and Farnell seem to have better search engines.

    Colin =^.^=
     
  7. Joerg

    Joerg Guest

    Hello Colin,
    Ok, with so much data detail you need to go to the mfg sites. TI is
    pretty good and lists prices. So does AD. But you will be hard pressed
    to find 30MHz GBW in view of your other requirements such as 30V VDD,
    100ohms and 1000pF drive etc.

    The OP467 might come close but it'll cost your around $5 for a quad.
     
  8. colin

    colin Guest


    Thanks, Il keep looking, but the 100R+1nf are in series,
    Im not sure this is such a demanding load,
    anyway its just a filter before the vco,
    and the signal isnt changing much just needs to be stable.

    I could do it with a couple of transistors I gues.
    but I think il get a bunch of OPA228 as recomended by Fred and keep the gain
    at 5,
    they actualy look pretty darn good, even specifies 10% overshoot with 1nf
    load.

    TI like many sites is annoying as I have to specify what its use is,
    ie. I would never have described this as an audio application !

    Colin =^.^=
     
  9. Joerg

    Joerg Guest

    Hello Colin,

    If it can be done with a couple of transistors I would do that. Those
    designs have a much better longevity.

    Yeah, that's a nasty habit of the new generation of marketeers. The
    worst was when they called stuff "Excalibur" and nobody had a clue where
    to look. TI's site has deteriorated a bit but it's still quite good.
    They list a category under opamps that says "Greater than 50MHz". Also,
    they let you list all opamps they've got and then order them by GBW or
    whatever you like.
     
  10. colin wrote...
    The opa2277 dual is a grand part, and the A version is much cheaper
    than the LT1124 I've been using.* I see all the distributors have
    plenty of the miniDIP package in stock, but are sold out of the soic
    package, so I'll have to stick with the LT1124 for now. For example,
    Mouser shows 1,200 on order but with a 11/27/2006 Estimated Ship Date.
    TI's site shows the opa2277ua with >10k in process for next 29 Jan.
    Yep, a popular part, insufficiently produced and badly backed up.

    * The OPA2277 is spec'd at 3nV noise, whereas the LT1124 is 2.7nV,
    which is 10% better! Guess that's why LTC gets the big bucks. :)
     
  11. colin

    colin Guest

    thanks, Farnell have the single in stock but not the dual 2228,
    Ive found a faster part ad8034, only 24v but single supply rail to rail op.
    shame about the input diodes .. maybe you might not like the higher noise
    but still good enough for my app.

    Colin =^.^=
     
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