Hi in a previous video linkedin down below and at the end. if you haven't seen it where we looked at, uh, finding, uh, potentially any modern, more modern, higher performance replacement for the Max 42 38 42 39 used in the micro microcurrent which is like a 12 13 year old design at least. Uh, something like that and well, we looked at a few chips uh, on the market and really just like superficial top end look, but I wanted to actually have a more comprehensive look and actually one of the chips that we covered and looked at in the previous video even though I sort of dismissed it based on like some top level specs this video, we're going to have a shootout between these two particular chips. We're going to go deeper into the data sheets on both of these and look and see how those compare because we might have a winner winner chicken dinner here that is a better Op-amp than the Max 42 38 42.

So let's take a look at it. Uh, the one we're going to take a look at today is the Opa-189 that's actually and also Uh 2189. so it's available in a single one and the Opa-2189 is a dual version and it's available in Soic packages 23 and a V-s-s-o-p package as well. so choose your flavor.

Here we go, I'll whack the Dave head up the top for you. I know there's a lot of floating Dave Head aficionados out there and yes, I have flipped my image now so that if I look over on the right hand side here, it's going to be right. If I look over on the left hand side here, my eyes actually follow. So let me know.

If you like Floating Dave, head up the top or you like it down the bottom. Um, yeah, we looked at this and I had a few interesting things in that uh, it was. It had mux-friendly inputs. Oh, you didn't have any uh, clamping anti-parallel clamping diodes in it.

Which means that it doesn't interrupt your your mux you know, switching and things like that. So yeah, it's got Mux friendly inputs here and also Rfi Emi filtered inputs that's always good and it's actually got a wide supply voltage range 4.5 to 36 volts And that's one of the uh first things we need to look at because if you compare that to the max 42 or 39, this one is only 2.7 to 5.5 volts supply there. So your maximum dynamic range can only be 5.5 volts. And dynamic range is important when you're talking about a current shunt amplifier like the microcurrent.

It's one of the major things because when you're measuring a device that switches between, say, a sleep mode and a higher power mode like this, Um, then you know it wakes up and it transmits via Wi-fi or does you know some processing and then shuts back down. That's you. know, the dynamic range you're trying to measure. and if you don't have a sufficient voltage range there, your it limits the dynamic range you might have to range, switch, and things like that.

So this is essentially part two of designing a better microcurrent by the way. and I'm going to do future videos on this. so the Opa189 wins out on supply voltage range. Dynamic range goes up to 36 volts.

It's actually quite remarkable. Now of course, one of the major requirements is Uh. offset voltage of the Op-amp and the max 42-39 of course is uh, famously like, nor ultra low. 0.1 volts are offset and geez, I can't really control my mouse very well.

can I? 0.1 volts offset voltage there. And that's incredibly low. There isn't basically nothing else on the market that can really match it, but as we saw last time, the Devil is in the detail. You need to go down here.

and let's have a look at this graph here: Input: offset distribution and they don't tell you how many different parts. But basically this is the production test. uh, distribution of they you know, take hundreds of different chips, they measure them, and they basically bin them in a in this case, uh, it looks like a 0.3 micro volt bin here. So you can see that 40 percent of the chips here are within plus minus 1.15 micro volts.

And that's you know, that's pretty tight. Of course this is going to be a like a production bell curve. Geez, I'm not very good at drawing a bell curve, am I? The mouse isn't very good for this sort of thing. I need one of those huge big tablity things that I can, you know, ride on.

Anyway, I do have my Microsoft surface, but yeah, so yeah, you can see it basically extends out uh, pretty much to uh, plus minus one micro volt here. And of course, if you look at the actual Um specs, they are actually higher than that. Uh, we need to never look at these top level uh specs by the way. So let's actually go down and have a look at the real input offset voltage.

Note One: Typically 0.1 max of 2 micro volts here. Now this is where the the maximum value of the 189 is not going to be as good. But let's look at note number one: Always look at the notes, see what they have to say for themselves. There, it is, uh, guaranteed by design therm.

A couple of leakage effects uh, preclude measurement of this parameter in production. So basically they don't production test every Uh unit. but they screen during production tests to eliminate defective units that are outside that maximum 2.5 volt input offset voltage. Hang on.

Why is this one 2 micro volts here? and it's 2.5 here. What's different Voltage range: 2.7 volts to 5.5 Common mode equals V ground command V V Output Vcc on 2 for V out. Aha, this is over the full temperature range. There you go.

Whereas this table this electrical characteristics table here is over only the 20 like at nominally 25 degrees. So they've got two different tables. so you know, trap for young players there. don't necessarily take you know this table for granted because you know you might go.

Oh, it's two micro volts maximum here. That's beauty. But who knows. The next table over here, it could have been 20 micro volts.

You just never know. But it's fairly tight. You know it's almost tight. Not quite tight as a nun's nasty, but pretty close 2.5 micro volts there over the full operating temperature range.

Now the 189 I don't believe is as good as that. So top level here. Yeah, Three micro volts maximum. It's you know, it's getting pretty close.

So let's go down to information: Electrical characteristics: This one's at normally, uh, 25 degrees offset voltage here. See, it's not as tight on the typical. In fact, it's like it's four times worse, right? So you might think that this particular chip is like, oh, it's four times worse. not nearly as good.

Won't even consider it. Okay, this is where you need to dive deeper into the data sheets and have a second look at these sort of things. which is what I was always gonna do. And the maximum isn't that much more than the plus minus two.

But technically this is a worse chip in offset voltage, but that's not an absolute show stopper if it has advantages in other areas. be it other performance like bandwidth and noise, and other things which we're going to look at in this video, albeit price. If this was like 10 times cheaper, you'd go Oh yeah, Oh, you know, happily live. You know you might happily trade off.

You might not, but you might decide. Yeah, I'll happily trade off. you know, four times worse. Typical input offset voltage for you know, half the price or in one tenth of price.

I don't know. I think the price is quite similar between these chips, by the way. So yes, here's an example where data sheets can differ. The maximum one we saw had completely different tables for different voltages.

This one is, uh, ambient. typical around ambient of 25, but they include a separate line item here for the full range. So there you go. Plus minus four.

We had plus minus two and a half on the maximum unit. So not as good, but may not be a show stopper. So here is the devil in the detail. Let's go down to our production yield down here and see what we get.

Aha, Offset Voltage Production distribution. Once again, a number of units. There you go, they tell you. Excellent.

Um, yeah, they give you. You know your statisticians out there. There you go. You can look at all that, but look, it's you know.

Once again, it's that bell shirt and bell-shaped curve. You're going to get that on practically any production uh type yield parameter, not just input offset voltage. You get that on almost everything. Let's take say, 40 percent.

You know there's three up here at around 10 12, so let's take three or four of those right, Which is equivalent to the one bar we saw on the Maxim and it's within. It's not as tight, right? so four of these you extend that down. It's like plus minus 0.25 so it's a little bit worse, but not a huge amount. But look at the maximum you remember when the Maxim one it extended down to minus one here and plus one here.

it's basically the same yield. It's not as tight. the maximum one was like tighter like that. This one's a little bit wider, but the maximums of plus minus one micro volt here they aren't like too dissimilar.

It's almost an identical chip. and it's usually not wise to design your uh products around the fact that it's got a nice tight production curve like this because that could vary over uh, time, and production processes and all, uh, sorts of things. So this is only a typical thing. This is not a guaranteed that will only guarantee you you know what was it? Three? Yes, it was plus Minus four.

and by the way, the dual version. the 2189 actually has a higher offset voltage, so just be aware of that some of the parameters in here if you go deep enough, they will change for the dual part or a quad part or whatever as opposed to a single. So there can be advantages. Even though it'll cost you more to use that single chip, uh, part.

they can actually be performance, uh, advantages there. So anyway, and this is at a vs of plus minus 18 volts. Once again, they don't want. They won't give you the offset voltage for lower voltages.

It could change at lower voltages. That's something you might have to measure in your design, for example. But anyway, they measured lots of parts here and it's it's. basically the same, you know, plus minus one.

But as I said, it could be plus minus four over here. so that's what they guarantee. But when they go measure them, look, you know, Bang on. So they're going to tweak their production process, so it's there.

They're always going to tweak it so it's pretty much in the center. Like this. It might shift a little bit, but you know, not a huge amount. but the actual yield, you know, could get bigger something like that.

but they would have to change something for that to happen. So yeah, interesting huh? And also the Uh 189 has, um, the same yield for input bias, uh, distributions, and input offset, uh, current as well. If you're interested in those sort of things, which if you're down in your pico amps, you know you're really, you know could care about that sort of thing. Um, so yeah, they've got the yields for that, so I'm going to call those practically equivalent on input offset voltage.

Or at least good enough for Australia anyway. So let's go back to the Maxim. What's the next thing we need to care about here? Well, it's going to be our Gained Bandwidth product. Look at this: the Max 4239.

That's the which with the minimum gain of five by the way to get that, um, 6.5 megahertz Gain Bandwidth product. And I've done an entire video on uh, cascading amplifiers for Game Bandwidth products and I'll have to link that one in because it is an excellent video. But once again, never take the top level spec for granted. Always go to the table.

The Game Bandwidth product here. Uh, with a load of 10k 100 path measured at 100 kilohertz. When it doesn't tell you what gain that's measured at those, some data sheets will tell you that. but yeah, normally 6.5 megahertz.

Okay, so is the 189 better? Well, let's go to the video tape 14 megahertz. Let's go check it out. And the slew rate, by the way, might check that out in a second. But so Game Bandwidth product.

And they actually specify the Unity Game Bandwidth here. The Unity Game bandwidth is already bigger. It's eight megahertz. Um, but the Game Bandwidth product at the gain of a thousand.

As I said, some data sheets do tell you that it's 14 megahertz, so this is a wider bandwidth Op amp, so that's a win for the 189, it's higher bandwidth and of course, bandwidth is one of the important criteria of a shunt amplifier like the microcurrent. So anyway, slew rate: 20 volts per microsecond. And of course, because it's got a lower bandwidth, the maximum is only one maximum is only 1.6 volts per microsecond. so like more than an order of magnitude better slew rate.

I'm going to have to start writing a list of actual parameters here and which one wins. All right, what's the next thing we care about? Well, we do care about our supply current, so let's have a look here. The Maxim Device: 600 microamps supply current per amplifier because we've got multiple amplifiers, It does add up. if we go down here.

we're talking about like a maximum of 900 microamps, but you know I'll take them at their word. Of the 600 microamps, we don't care about shutdown because we never shutting it down and the 189 1.3 milliamps so it consumes twice the current. so that's a win for the max 42 39. But you might be willing to trade off and I'm certainly willing to trade off in this design supply current for bandwidth, noise, and other performance parameters.

Okay, next thing, uh, let's just go short circuit current. You know what can this, uh, sucker drive? Plus minus 65 milliamps for the 189 and 40 milliamps for the Maxim. So that's a win to the 189. Now of course, it's important.

It could be an absolute showstopper if you don't get your ground sensing input and rail to rail performance because, well, you may not care about these things in this particular case. Yes, we do have to sense uh to ground if you do it in the single, uh, uni polar supply configuration. Doing the bipolar supply configuration doesn't matter. But yep, rail to rail output includes negative rail, so they both get a tick.

Now another one of the biggies is actually noise here. Uh, because I've actually done a whole video which is excellent by the way. Not that I like to toot my own horde, but I think it's really quite a great video where I talk about measuring noise of Op amps and I actually demonstrate it on the bench with a dynamic signal analyzer how to measure the performance. And I'm going to be buying these chips and actually are comparing these two chips in a future video in terms of like their noise, floor and response and stuff like that.

Anyway, Low noise: 1.5 micro volts from Dc to 10 hertz. Well, let's go and check the video tape. Now, I won't go into the differences between noise because I've done a whole video on that. But basically there's two ways you can measure either peak to peak noise like this in voltage or you can talk about noise density like this, which is over a given bandwidth.

Um, it's you know, spectral density. Uh, pretty much. And that's in. uh, Nano volts per root Hertz Capital N Volts per Root Hertz? Oops.

Somebody give that look. They've used Nano volts up here. and they've used Capital N volts down here. Oops, Yeah, Great stuff.

Anyway, for one kilohertz bandwidth, which is a typical Uh specification: 30 nano volts per Root Hertz for the Max 4239. So you basically have to multiply this factor by the bandwidth. It's not divide. You actually multiply it by the bandwidth and that'll be your total output noise basically.

But they give us a figure like this, but that's only the low end. If you care about, uh, that sort of stuff, we necessarily don't necessarily care about that. So anyway, 30 nano volts per root Hertz Dave Head's got to go down the bottom for this. Uh.

17 nano volts Rms. They actually are noise. If it's in volts, there's always Rms noise, by the way. So that's uh, up to 10 Hertz.

So 0.1 microvolts? Uh. peak-to-peak Wow. That's more than an order of magnitude better. The Max 4239 was 1.5 micro volts peak-to-peak This is 0.1 Wow.

That's over the 10 Hertz range. And Nano volts Uh, per Root Hertz the same one kilohertz bandwidth here 5.2 versus 30 for the Maxim. Wow. Six times lower.

So this is a substantially lower noise op amp than the Max the max 4239, which you'd kind of expect because it's drawing like, what, uh, three times the current, three four times the current or something like that, so you'd expect that. Um, it's you know, usually you're gonna trade off supply current for noise. That's one of the typical uh things, but if you're willing if you're happy to do that, then Wow. This is a substantially lower noise Op-amp And of course noise gets multiplied by the gain as well, which hopefully will show this in future videos when we build these up and actually compare them.

but that is a huge tick. Um, for the 189s, That could be one of your most important parameters because the microcurrent is not exactly a low noise device. So yeah, this could have huge advantages and things like: Input: Common Mode voltage range: V Ground -1 That's going to be the same common mode voltage range. Yeah, I'm not not too concerned about that.

Let's have a look at the common mode rejection ratio. Not really, uh, important for the microcurrent, but worth a squeeze. Typical 140 are down at 2.25 volts. So yeah, there you go at the lowest voltage: 140 db and they don't note one down here.

Oh, they don't test it. That's the same. Yeah, 140 Db Floating Head Dave Again, Input: Uh, Bias Current: This is important because uh, you need a low input current due to the topology measuring across a 10k source impedance on the nano amp uh, range. so you know you don't want to sort of, uh, you want a decently low bias current there.

We'll read the note in a second. but basically one puff. One pico amp there. Um, Input offset Current is two pico amps.

This is for the maximum. What does note 2 have to say for itself? In plus and in minus I gates to Cmos transistors. Typical input bias currents of one Picon Cmos leakage is so small, there's impractical to test and guarantee in production. They're screened uh to eliminate defective units.

So they basically have a go no go for input bias current. But it's basically so. One pico amp is like so low you don't need to worry about unless you're some ridiculously ultra critical design. Uh, where? Yeah, it would matter.

and then you're going to pay 10 bucks for an Op amp that specifically, you know, tests every unit for input offset current. Oh, here we go. Input Bias Current: The 189. Oh, it's 70 times worse.

That's a lot. So big tick for the 4239 there. And it's the same for the Uh dual part as well. I'm surprised it's not a little bit different there.

but and the input offset current as well. 140 pico amps. So so once again, that's you know, hugely. uh, more than the Maxim device.

But in this particular case, I'd have to run through the numbers. but I I think we're okay There 70 pico amps is. Yeah, you know it's worth considering and looking at, but it's probably not a show stopper. So input bias, current.

You know you wouldn't throw this chip out just because of that unless you really needed. you know, ultra critical, uh type stuff which we don't necessarily need because as I said, I'm happy to trade off supply current like and accuracy and stuff like that if you get higher bandwidth and lower noise. um, and other advantages. So yeah, it's it's yeah.

I wouldn't rule that out. Okay, and we don't really care about crosstalk or total harmonic distortion. I wonder what it is? Look at this. Oh, your audio falls.

Look at this. .006 Wow. but you know they can still hear that. Yeah, do Maxim even have total harmonic distortion? I don't think they do not.

Couldn't give a rat's arse. I don't blame them. Okay, another thing we probably want to have a look at here is overload recovery time because if you drive the Im probably done a video on this. If you drive the input to an Op amp hard and make it saturate, it actually takes time like milliseconds like which is quite significant time for the signal to recover.

And for a device like the micro account that's designed to measure like really fast changes in like sleep and wake-up currents and things like that if you, uh, especially if you auto-range and you don't if you're outside the dynamic range and then you're forced to auto-range you're saturating the Op-amp Unless you take measures to clamp it and things like that and prevent it, you're but then you need extra parts and extra design and tweaking. We won't go into that for this video, but that can really impact what you're going to see on the scope. and things like that. You may see this like decay curve like this, you might think, oh, that's what my products actually doing that.

No, that's the settling of the, you know, settling time of the Op amp. Doing it anyway. Overload. Uh, recovery time here.

Let's have a look. Once again, this is, uh, nice. It gives you in different number of bits like 0.1 percent, uh, which which equates to like a 10-bit analog to digital converter, so it's nice of them to put that in there. It was a nice touch.

It just means that you don't have to get out your confuser here and actually calculate. uh, things. You can just go. Okay, I've got a 12-bit Adc that I'm using, you know? So yeah, what? Roughly 0.025 percent is 4.1 milliseconds? Anyway, let's take the 0.1 percent because that is a typical recovery uh time.

and a 3.3 milliseconds for the Maxim and overload recovery time for the 189 320 nano seconds we're down in the nanoseconds and all these milliseconds. Rubbish. Or micro seconds? 320 nano seconds? How many orders of magnitude is that better than the maxim? That's really incredible. So like recovery.

Huge tick for the 189 and that's a it can be a massive advantage in a product like this. so more winner. And let's look at the settling time as well. Uh, to 91? 0.1 percent? 0.8 microseconds there? Once again, that's like 800 nanoseconds.

We're down in the nanosecond region for a 10 volt step. Wow. And over here. the settling time? Uh, you know, 0.5 milliseconds.

So 500? So wow. The uh. the 189 just blows it out of the park. All right.

So what's actually, uh, left we're getting. I'm getting down to the dregs. Really maximum closed loop gain? Not too concerned about? well, if you want to run typically a thousand here, I don't know if the 189 is going to have that. I don't think they have a maximum closed loop gain there, but we only want to close loop gain of a hundred.

I'm sure it's going to do the thousand. We've got open loop again there, but it won't tell us the maximum closed loop and that's fine. Maximum output impedance here 380. Ohms, do we care? Nah.

the maximum is not even going to tell us that. Okay, I'm struggling to think of anything else simple to offset. long term offset drip? Like, we're not really concerned with offset drift. Uh, 50 nano volts per thousand hours? Like you know? you really have to be.

you know, squabbling over details there? Yeah, I don't think the Ti's are going to tell us the drift there. Oh no, they specify this as zero drift. It's it's specifically zero drift. So yeah, I can't see how this 189 is not a winner.

Um, over the max 4239. There might be a show stopper in there depending on your uh design. And once again, like, we could go and quibble over the graphs and things like that. But I think we've covered, um, almost everything we care about: offset voltage, supply, voltage, gain, bandwidth, product, um, supply, current input, uh, short circuit? uh, current rail derail stuff, noise, um, a bias and recovery at times and slew rates and yet positive overload recoveries and things like that.

Now we've got the you know, there's the step response. and we're down in like nanoseconds. Hundreds of nanoseconds per division. Absolutely brilliant.

I can drive, uh, overshoot with uh, and versus capacitive loads and things like that. Like, you know, you can go into lots of little intricate details like this. But I, uh, there's the output impedance uh, versus frequency. That's kind of groovy.

but yeah, really. Um, we've seen more than enough that warrants us to buy some of these chips and try them out and actually do some A B comparisons. Uh, like, in terms of, you know, bandwidth, noise, particularly offset voltage, and things like that versus the max 42 39. And here's the internal block diagram here.

As I said before, this is like a zero drift or a chopper amplifier. There are differences between the Uh Zero drift architecture provides ultra low offset voltage, near zero input, offset voltage over temperature and time. Uh, choice of architecture also offers outstanding Ac performance Ultra low broadband noise. Yeah, I'm really interested to actually compare the two zero flicker noise I've done.

I think I've never done flicker noise in my noise. uh, tutorial when operating below the chopper frequency. But yeah, basically it's got internal clocks which are usually they're a divide clock so it's not at one fixed start frequency so which can help or it depends and sometimes you want to like filter that out, you want it to be exact so you can notch filter it out or something like that. But anyway, we don't care about that ripple reduction feedback loop.

Anyway, it's it. It's a chopper amp uh, slew boost circuit? Well, that's how we get our fast bandwidth beauty. But anyway, I'll link these data sheets down below. I'm this video is long enough but you can go in here and it's got Emi rejection stuff which is really great and things like that and always don't just look at the tables, of course, go in and actually have a thorough read of the text in here because they can You know, alert you to some things that you may not have picked up in the tables and things like that so I won't go through and read stuff like the read all these things.

The video has been long. I love the equations. look at that. Beautiful.

There you go. low side current monitor. That's what we're doing. There's our 100 milliamp shot.

We use a 10 milli ohm uh, shunt, 10 ohms and 10k in the, uh case of the uh, current microcurrent design. anyway. um, a driver for a 24 bit Delta Sigma converter. Stuff like that.

They've got layout tips and things like that. Nice. I'm going to call it this is a winner Winner chicken dinner. or at the very least it's absolutely worthy of.

I'm going to go out and buy some of these chips and I'm going to do a direct A B comparisons with the 42 39. So um, hopefully we'll have that in an upcoming video. So there you go. Don't always take these top level specs or one particular thing like you know.

Three are the Uh Maximus 0.1 micro volts. This one's 3 micro volts. Oh, that's horrible, you know? So yeah, it's worth digging into the details because check this out. Focus your bastard.

So there you have it. Switch off the Dave Head mode. You can see that the 189 wins in lots of categories and sometimes wins hugely. The only one where the 4239 really won out hugely was the input bias current.

So 189 very worthy, um of being considered for a new design microcurrent. There you go, But I subject to actually getting some cheap soldering in and doing some real world measurements, especially like noise. I'm very interested in the noise measurements and uh, stuff like that Anyway, hope you like that video. I'll link in all those other videos down below measuring noise and stuff like that and I hope you found that useful.

If you did, please give it a big thumbs up. As always, discuss it down below. so hopefully this is like part two of a multi-part series. I don't want to specifically say it's a proper design series, but I'll be doing videos from time to time on this.

So yeah, catch you next time you.