Is there a dual equivalent to the quad LP324?

I've never seen this. Can you expand on the circumstances? I tend to use LM324s as sense amplifiers because they are so cheap. I'd hate to have one blow up my pass device.

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Regards,
  Bob Monsen

"Animals, whom we have made our slaves, we do not like to consider our
equal."
 -- Charles Darwin

If the + input goes too negative, even with limited current into the input, then the output will slam to the + rail. This can cause your circuit (not the op-amp) to latch up. Just don't do that.

Best regards, Spehro Pefhany

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"it\'s the network..."                          "The Journey is the reward"
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Oh yes, the LP324 is a worse performer.

NT

Hello Jim,

Yeah but, us analog folks must use what's there. Whatever is in the can and doesn't cost much. When Uce dips below 300mV I just don't feel comfy anymore unless I know the process parameters. Which they usually won't disclose like I had that happen on the MSP430 (TI lost a design-win because of that).

The next project will need the same thing but scaled down in voltage (1.5V-3.5V). For you that would be a piece of cake, for me it looks like no-can-do because every quad amp in that range is well over 25c a pop. Oh well, good thing that we all learned to be content with discrete transistors which are only 1.5c or so.

Regards, Joerg

Hello NT,

But look what it still can do at under 100uA quiescent. It's basically an LM324 that was on the Atkins diet. If you can live with 1/10th the slew rate and GBW as I usually can in LM324 apps it is great. The only downside is the higher cost which is why I usually go discrete on ultra low power designs.

Regards, Joerg

If you never saw it, then you probably implemented your design correctly.

I saw this when measuring the tiny voltage on a kelvin-connected current sense resistor and maybe the ground at the op-amp supply was not *quite* the same as the ground point at the sense resistor at all times ;-).

You have to make sure that the common ground is at the highest-current junction so the whole circuit operates relative to that.

At least the LM324 does not latch - some chips include latching in "undefined behavior" (bit like what's included in the industrial definition of "meat", but I digress).

Hello Frithiof Andreas,

Use a common and full ground plane. I always do and never had any problems with architectures like that of the LM324.

Regards, Joerg

hi there

Yes, and I think thats the constructive way to look at these parts. I always puzzle at people moaning about the 324, its an engineering victory in my book. Any engineer knows the job is to meet all the requirements* at the lowest price, and the 324 is very useful in this quest. It does all sorts of stuff, and at remarkaly little cost. The

324 is one of those parts that belongs on the first choice list for many engineers. Any position where specs and speed are undemanding, its 324 time.

If you want to push things harder, there's an even lower cost opamp replacement for some apps, the 74 cmos hex invertor. Not an opamp of course, or even very close, but will do some of the jobs an opamp will, and shave a few more millipence. It can switch or go linear, gate signals, add and subtract, invert and buffer, do limited logic, and ocasionally its even good enough as a rough voltage threshold detector. Its cheap, fast, and eats nothing when railed.

Back to serious opamps, the 324 can do a wide range of things. Its an opamp. I'll admit to never having considered making an smpsu out of one though. Is that workable? I realise it can give several times 6kHz out to run a pass transistor (a point not always appreciated), so I suppose it is.. Cant imagine it being a sensible choice though.

NT

• by all I mean all, function, reliability, performance, appearance, energy effciiency, cost,

Hello NT,

The LM324 would be very high on my list for the hall of fame. Looks like a genuine Robert Pease or Bob Widlar design although I don't know who the chief design engineer for that one was. The most useful feature is the common mode input range to ground.

The only downside is unpredictable quiescent current when setting it somewhere to the side of center. This trick worked nicely for CD4000 series parts with their weak output devices. Also, even a 74HC becomes iffy below 2V and you have to go there in a two-cell alkaline design.

Often I used 1/4th LM324 in the feedback loop and two sections of a hex Schmitt inverter would do the PWM stuff. This way I had some designs going in the 500kHz to 1MHz range while most of those expensive chips were crawling along under 100kHz. Heck, the last one was even current mode.

Regards, Joerg

I saw it once in a 400kW motor contoller, on board a ship. We had a unipolar supply for the LM324, which measured DC bus voltage. problem was, supplies on ships dont have "earthed" neutrals, so the control pcb was floating :) wrt the DC bus. If it happened to float in one direction, we had 2kV CM range. In the other direction, we had about 40V CMR, beyond which the opamp would phase reverse, and the drive would trip on over-voltage :). The solution was to use a split supply, which we cannibalised from an RS232 interface.....

Cheers Terry

Tom Frederiksen designed the LM324, as well as the LM339 and LM3900.

I'm surprised that you thought it might be a Widlar design. I doubt Widlar would have bothered with such a plebian project, but if he had, he would have come up with a much trickier circuit.

To me, it doesn't look anything like a Pease schematic either, but I can't explain why I think that.

Also, in those days there was no "chief design engineer" for something like an op amp - one engineer did the whole circuit design, and maybe even the layout.

I was nearly 10 years into the "biz" before there were layout designers separate from the circuit design.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
               The harder I work the luckier I get.

Hello David,

Thanks. AFAIK he worked with Widlar and Pease.

Yeah, the LM324 is more like a volks-amp. But it sure made many designs a lot easier. It runs circles around the 741 (which I never found all that useful).

That was the same in HW engineering in those days. Some layouts had to be done with that spaghetti tape if you couldn't secure a long enough time slot on a mainframe console. Very messy. And by evening time the fingers looked like you had just applied stucco without gloves.

Regards, Joerg

But worked first with yours truly at Motorola in the early-mid '60's... we even shared a cubicle for several years.

He references some of my work on page 14 of his book "Intuitive IC Op Amps".

Then on page 15, Fig. 1-13, "A Basic Op Amp", he shows the guts of what is essentially an LM324... using my style of differential-to-single-ended current mirror.

Widlar gets credited for more sophistication than he actually delivered... unless you think the 709 and 741 are clever ;-)

I'm scratching my head also. Has Pease actually done a complete chip or was he always filling in details from the sideline in his role of Staff Scientist?

For many years my world was built of LM324's and LM339's ;-)

Then I switched to TL084's as my OpAmp of choice, but I still love the diverse usefulness of the LM339.

Yep. I still have the die photos hanging on my office wall.

When I did I/C layouts, I doodled it up on quadrille paper then used Rubylith (cut and pull-away tape) to make a negative, thus I didn't have the mess of stick-DOWN tape.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
               The harder I work the luckier I get.

Hello Jim,

Wow, the world must have been small in those days. Kind of like ultrasound today where most folks know each other.

I liked the 709 when I was young but shunned it a lot because of its cost in those days. Went discrete, usually. Except for hobby when I snapped up a huge bag of, well, re-labeled 741. They all had really bad offset but were otherwise fine.

Do you know who did the LM331 V/F converter? Could have been a Pease creation but I don't remember. That chip is a heck of a design. If they hadn't kept the price up I'd have used containers full of it.

The other famous ones I remember were the uA723 with its nice noise behavior. Then there was the pocket rocket uA733. Harris had blazingly fast chips as well but they cost a lot and got very hot.

I used the TL082 a lot as well. Nice chip, but compared to the quiescent current per amp of the LM324 quite a guzzler. IIRC they kept the TL07x and the TL08x series with one being lower noise but I never found a significant difference.

Not much Rubylith in Europe :-(

Occasionally I still design the more nasty parts of a circuit on vellum. That is almost like a ride in an old Bel-Air.

Regards, Joerg

[snip]

We may know some of the same people. I did TVG chip designs for ADR Ultrasound (when they were here in Tempe, AZ) and also Acoustic Imaging.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
               The harder I work the luckier I get.

Hello Jim,

Yep, was there a few times. Unfortunately they are gone but the engineering will always continue. Just one town to the east, in Mesa:

At ATL we called the time variable gain "time gain control" or TGC. What we did was a hybrid though. Lots of dynamic range.

Regards, Joerg

Yes, but unless you worked with it day in and day out and developed that magic touch with the exacto knife, you wound up cutting through not only the ruby but the lith also and wound up with a mylar spaghetti pile.

Jim who worked his way through freshman year with red and blue tape, black donuts, and huge sheets of mylar.

This was at Motorola. It wasn't free-hand... there was a slide bar guiding the knife and it was controlled cutting depth.

Although I did, on occasion, take a double-bladed knife and cut free-hand "swirlies" just to annoy the layout guys ;-)

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
               The harder I work the luckier I get.