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Single Supply Op-Amp

Discussion in 'Electronic Design' started by Ken McDonald, Oct 30, 2004.

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  1. Ken McDonald

    Ken McDonald Guest

    Can someone recommend a single supply op-amp with better specs than an
    LM358?

    Thanks,

    Ken McDonald
     
  2. CFoley1064

    CFoley1064 Guest

    Subject: Single Supply Op-Amp
    Lots of them.. What do you need?

    Chris
     
  3. Repzak

    Repzak Guest

    What are you needs ?

    which application ?

    Rail to Rail ?

    Kasper
     
  4. Ken McDonald

    Ken McDonald Guest

    I guess I'm looking for a single supply dual general purpose op-amp that has
    higher gain and higher slew rate than an LM358. Something newer I guess.
    I'm working on an infrared receiver right now, but am always throwing some
    kind of amplifier circuit together.
    Rail to Rail would be nice, but definitely want the output to go to ground.

    Ken
     
  5. Jamie

    Jamie Guest

  6. CFoley1064

    CFoley1064 Guest

    Subject: Re: Single Supply Op-Amp
    Hi, Ken. Usually, the LM358/LM324 are looked at as starting points. They're
    popular because of the balance of features at a dirt-cheap price.

    I'm hearing:
    Single supply dual op amp
    Higher gain than LM358 (GBW = 0.7 MHz)
    Higher slew rate (SR = 0.3V/us)
    Other than that, everything else at least as good as an LM358.

    Of course, you'll have to pay more. One good choice for a "super LM358" is the
    OP292, available from Analog Devices. The non-improvements include:

    Minimum single supply = 4.5V
    More expensive: DigiKey Prices
    LM358NNS-ND $0.54 ea.
    OP292GS-ND $3.02 ea.

    Everything else is a plus. Check it out:

    http://www.analog.com/UploadedFiles/Data_Sheets/882565314OP292_492_b.pdf


    Good luck
    Chris
     
  7. Pooh Bear

    Pooh Bear Guest

    You don't *have* to use so called 'single supply' op-amps for single
    supply applications.

    It depends on the application.

    So called 'single supply' op-amps usually include ground in the input
    common mode spec - that's the point of them.

    AC coupled signals as per the OP's example don't need this.

    What's the application - then a sensible suggestion can be made.


    Graham
     
  8. Pooh Bear

    Pooh Bear Guest

    No op-amp that I know of has an output that actually goes to *ground*. For the
    simple reason that there will be an active device between the output terminal
    and the ground ( V- ) terminal.

    CMOS types may typically get within a few tens of millivolts.

    If we knew more about what you're doing it would help. Of course the output can
    go to ground if you're working with split supplies.


    Graham
     
  9. Norm Dresner

    Norm Dresner Guest

    The output can go to ground if you're willing to use a pull-down resistor on
    the output. There's at least one IC OpAmp that was made with an on-chip
    resistor that way.

    Norm
     
  10. Bill Sloman

    Bill Sloman Guest

    There are lots of parts around that satisfy that constraint, and more
    every year.

    The Linear Technology LT1006 (single), LT1013 (dual) and LT1014 (quad)
    parts were introduced early on to satisfy the demand for something
    slightly better than the LM324/LM358. Go to

    http://www.linear.com/

    and dig up the data sheets - I've checked that they exist, but I
    suspect that the URL's that got me to them might not work the same way
    for a second enquiry.

    Farnell stocked the LT1013 and LT1014 the last time I looked, but the
    LT1006 was a bit harder to get hold of.
     
  11. Bill Sloman wrote...
    DigiKey stocks them. The Linear Technology version is expensive,
    e.g. LT1013CN8 at $4.25 each, but the TI LT1013CP version is more
    reasonably priced, at $1.40. Both feature a nice low 300uV max
    offset voltage. As far as the LT1006 single opamp is concerned,
    DigiKey has this LTC-only part, $2.88 each. It's getting scarce.
     
  12. Winfield Hill wrote...
    I should add that the LT1013 is a favorite of mine, over the LM358.
    And in the cases where four opamps are handy, the LT1014 of course.
    For cost-sensitive designs, there's TI's LT1013DD, $0.43 qty 1k,
    with 800uV max input offset.

    Besides a low offset voltage, these chips have circuitry to prevent
    phase reversal (* see below). There's more, as LTC says, "Although
    supply current is only 350mA per amplifier, a new output stage
    design sources and sinks in excess of 20mA of load current, while
    retaining high voltage gain. ... Crossover distortion, so apparent
    on previous single-supply designs, is eliminated."

    * "At the input, the driving signal can fall below 0V— inadvertently
    or on a transient basis. If the input is more than a few hundred
    millivolts below ground, two distinct problems can occur on previous
    single supply designs, such as the LM124, LM158, OP-20, OP-21, OP-220,
    OP-221, OP-420:
    a) When the input is more than a diode drop below ground, unlimited
    current will flow from the substrate (V – terminal) to the input.
    This can destroy the unit. On the LT1013/LT1014, the 400W resistors,
    in series with the input (see Schematic Diagram), protect the devices
    even when the input is 5V below ground.
    b) When the input is more than 400mV below ground (at 25°C), the input
    stage saturates (transistors Q3 and Q4) and phase reversal occurs at
    the output. This can cause lock-up in servo systems. Due to a unique
    phase reversal protection circuitry (Q21, Q22, Q27, Q28), the LT1013/
    LT1014’s outputs do not reverse, as illustrated below ..."
     

  13. Thank you for that explanation.

    Years ago, I struggled trying to fix a problem in a Benmar
    model 210 small ship auto-pilot.

    A 50 foot luxury pleasure craft was sold to the third owner at
    the same marina and the auto-pilot on board this vessel, from
    new, had never worked, according to the boat yard workers.
    Many people over the years had a go at trying to fix it for
    the previous owners.
    As soon as the auto-pilot was engaged the boat would
    just skew off to starboard. The boatyard workers were
    having a laugh at me as one of the many head scratching,
    technicians to look at this auto-pilot.

    After struggling a while, I was getting a bit fed-up with the
    derogatory remarks and continual "Have you fixed it yet?"
    from one particular shipwright at the yard, so to get back
    at my tormentor I decided to take the whole auto-pilot
    and interconnecting cables back to the workshop.
    That really pissed off the boatyard shipwrights because
    they had to remove the beautifully polished wood panels
    that the cables were hidden behind. That was a big job
    to do without damaging the polished woodwork too much.

    Back at the workshop where I could have the two control units,
    compass and motor drive unit in front of me I went through the
    auto-pilot, stage by stage, from compass unit to motor power unit.
    One op amp in an LM324 (quad) was the culprit.
    The output was phase reversed.
    I could hardly believe it!
    The output level was normal but just swinging the wrong way
    when the compass/binnacle unit was turned by hand.
    No wonder that fault was never picked up on board the vessel,
    it was just too hard to find when the units that make up the auto-
    pilot are spaced well apart on board the vessel.

    A new chip was fitted and the auto pilot worked fine,
    after all the preset pots had been re-trimed to somewhere
    near where they should be. Funny how pots must be
    tweaked when something doesn't work. :)

    I told my work mates about the phase reversal fault and
    they didn't believe me. I kept that faulty LM324 chip
    because I could hardly believe it my self.

    I made the mistake of telling the owner about the faulty
    part. He wasn't impressed about paying hundreds of
    dollars for a $2 dollar culprit. He coughed up the money
    OK after he had some fun playing with the auto pilot on
    his boat out in the estuary. I showed the owner how to
    adjust the feedback pots so that a steady course with
    mimimal hunting could be obtained. That eased his
    wallet open also.

    Thanks again for that explanation on the op amp phase
    reversal problem.

    Regards,
    John Crighton
    Sydney
     
  14. Tim Shoppa

    Tim Shoppa Guest

    TI has some interesting parts if you know that you'll be working with
    < 5V Vcc:

    cheaper than the LT1013 is the LMV358

    more expensive than the LT1013 is the TLV2472

    I don't understand what in their manufacture limits these parts to
    5V operation.

    Tim.
     
  15. I don't understand why TI needs to have pages and pages of opamps in the
    mouser, etc. catalogs. Why so many almost identical parts..
     
  16. RMC

    RMC Guest

    The absolute maximum voltage spec for ICs (i.e., the 5V for these op amps)
    is a function
    of the process geometry -- the smaller the device geometries, the lower the
    breakdown voltages.

    A good rule-of-thumb for .5 micron and smaller geometry processes is that
    the rated operating
    voltage is 10x the process geometry, thus

    0.13u = 1.1V
    0.18u = 1.8V
    ..25u = 2.5V
    ..5u, .6u = 5V

    Sometimes there are "think oxide" devices on a process, so you'll see
    converters with a 2.5V analog supply
    and a 3.3V digital supply - the thick oxide devices are used in the digital
    I/O section only for the logic interface
    to the outside wolrd and internally the logic runs at 2.5V.

    As for the pages and pages of op amps, there are differences in ft; slew
    rate; input offset voltage and current;
    input bias current; input common mode voltage; output voltage swing and
    output current; ability to drive a
    capacitive load; input noise voltage and input noise current, and of course,
    supply voltage and supply current.
    Apply these differences to more than 20 years of op amp design and you can
    see why there are pages and pages of parts!

    Bob Clarke

    PS: Analog Devices (my employer) also has lots of good op amps.
     
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