Hi. Sometimes you can come across a sneaky little trap in a chip that you use in that can really make you come a gutter in your design if you're not careful. And if you don't read the data sheets and specify your device correctly, let's take a look at an example here. Take a look at the Lm-2 Double 7/6 switch capacitor inverter.

Of course. this is like a variant of the classic R7 Double Six zero voltage inverter. So the Seven Double 600 be a classic chip if you want to invert a voltage rail. For example, let's say you've got a five Volt rail and you want to generate a Minus Five volt rail to power Op Amps for example.

like and these Seven Double 600 type of voltage inverters I Put that in quotes cuz like Seven Double Six Always like such a jellybean component. Not only are they're just, you know, xxx, Seven Double Six OHS but there's many variants of these voltage inverters. It also does fold each double in, by the way, but typically people use them for voltage inverters. When you've got to go from, say, you've got a 500, you want to generate a negative five volt rail because you've got an Op-amp in your circuit.

You want to pair it and and stuff like that, it's a very common requirement. so you might use one of these seven Double Six over voltage inverters to do that. Typically, you don't need a lot of current on negative rail of an Op amp. For example, you might only need a couple of milliamps you might need, you know, microwaves.

Occasionally there's a couple of high current types you might need a couple hundred million switch. This one is. Look, it's 200 milliamps output current, but we'll take a look at that. So these seven double Six over voltage inverters.

Now, they're actually not that easy to find parametrically at the the regular suppliers. like did you care Mouse Let's take a look at Digi-key here if you look at the categories down here. Okay, there's DC to DC switching regulators and that's actually where they're under. There's no category for these voltage inverters, so if you actually go in to I here it is DC to DC switching regulators here and you take a look at the function.

The topology here they're basically like, really isn't like they've got an inverted one here. step-up slash inverted which might thinks the case. But what Wah-wah-wah you've only got Three parts remain in here right? So like so we can apply the filter. And of course we just end up with these three from Rome semiconductor and they're not what we want anyway, so you can't sort by function there.

But if you go over to topology here and you have a look all the way down all the way with LBJ you got a charge pump down here and 126 devices so we can actually get and bingo is seven double six those will actually come up. But the problem is is that we're literally only getting the seven double six zeros here. We're not getting you more like specialized parts that look, it's pretty much only seven double six zeros. whereas you wouldn't find the one that we're actually looking at that Texas Instruments One You wouldn't find any of those more specialized parts.

So even this subcategory for the charge pump just as charge pump doesn't say charge pump inverters, just charge pump doesn't actually find all the parts available. And that's not always a good thing. Now mouse is actually made. Potentially a little bit better here because look, you won't find them in here.

Okay, they don't have the product type in this list here. You've got to know to go into switching voltage regulators down here. And then if you get into switching voltage regulators bingo, You do get the topology field and you get your boost invert in Sepik But you don't want that Really, you're more interested in Yeah, well. you could get your boost inverting ones and stuff like that, but you know you can start selecting those.

B can select you've got charge pump and you've got inverting for example so we can apply filters. We've got three hundred and twenty five matches remaining today and this one does show up. A few other switching voltage regulators does show up the you know more of your other parts and you will get Aha, Which we'll see later is some of the parts down here so you can get there, but it's not particularly easy or obvious and you can potentially miss a lot of parts out there that might otherwise be the best choice for your application. And you might stumble across something like this.

Some Lm-2 Double 7, 6 Switch capacitor inverter might look like it. It does the business. You know you might need a few tens of millions the output or something. It's got a high switching frequency here, two megahertz high switching frequency, which based on the classic Seven Double 6o design, actually implies a low output ripple.

So if we go over to the Classic Seven Double 6o here, trust me. I'll get to the point eventually. The trap with this chip I'm just taking a tangent here now the Classic Seven Double Stick. So it can be a very efficient chip.

or do you like near a hundred percent like 99 percent plus. but it depends on the switching frequency. It depends on the output impedance of the switches inside the chip because we have a look at the topology down here. like the basically they've got these output switching, a switch, capacitor, voltage inverter.

That's how it works. It switches the voltage on a cap and can invert or double the signal depending on how you wire it up. So the impedance of those are switches. They're also the the amount of output capacitance because you're going to have a typical circuit down here like this.

So general it like this capacitor here which is always called generally always call like c2. In this circuit this is the switching capacitor over here, but this one determines how much ripple you are, ultimately how much ripple, but it depends on the frequency, the internal resistance of the switches, the ESR of the capacitor, and so forth. a whole bunch of things. So that's why generally in most seven double 6o data sheets you will not actually find and a voltage ripple graph like you won't actually find ripple in any of the Y axes here versus you know output current.

You'll find output resistance here and you can see how the output resistance changed will it changes with the oscillator frequency and the oscillator capacitor value in here for example. So the higher the at a value that's see one value and it changes with temperature and all sorts of stuff. but they generally won't give you a ripple thing. that's because you to actually get the ripple you've typically got to.

You know, there's quite a complicated little formula here that takes into account the ESR of the capacitor c2 there. for example, the outputs are current of course, the higher the applecart the more you ripple you're going to get. It takes into account the frequency of operation and all sorts of things. So generally they leave it up to your own devices, but there are a couple of data sheets that will actually show it.

So one example would be the maxims if here which is the IRI CL 7 double 6o slash max 104 for basically you know pin equivalent type thing. So we can go down here and have a look and they will actually give us thank you very much. Maxim A very nice output ripple here. Output ripple in millivolts P 2 P Key Verses load current In this case the well, they've got more if they got two different load current 0 to 10 and 0 to 40 here and with load.

yeah they've got two different graphs. Good on maximum. Very comprehensive. Anyway, you can see that this a graph here is with this boost mode which is a frequency boost mode.

so the higher the frequency it's got a pin on there. you can just boost the frequency up so the lower the ripple you know. So at 10 milliamps output current you might get 50 millivolts peak to peak ripple here and but that will change if you just use the ICL 7 double 6o version on its own. you'll get B You'll get 200 millivolts ripple and so forth.

But and that's for a nominal output Passavant of 10 microfarads and a switching competitor of 10 microfarads so you know you can't The first trap is that you can't just read these graphs and go oh I'm gonna get 50 millivolts peak to peak ripple at you know like that's what the chips going to give. No it depends on the out the capacitance but the also what the ESR of the capacity use and all sorts of stuff so they don't actually go into that. So that's why these graphs can. A bit misleading.

You mean you might put your 10 microfarad cap in there but depending on the voltage rating and the D rating of the capacitance with the DC bias on the capacitor and like oh that's a whole video have I done a video on that I don't know, probably should. Anyway, capacitance can change with DC bias and and the type of capacitor whereof is x7r or our like a Wi-Fi view A real crap Wi-Fi view Class: Dielectric for example, the capacitance can massively drop and not be it might measure 10 microfarads on your LCR meter but you're getting your diddly-squat where you actually put it in the working circuit at the working voltage and whatnot. So yeah, you can actually get those sort of graphs but generally they won't give you that for a seven double six. Oh Anyway, let's get back to this and the trap with this.

sigh LM at Two Double Seven six and you might think this is a great chip because you picked it because it's available, it might be the right price. Doesn't matter, right? Let's just say that you found this chip two megahertz, which in frequency if you're familiar with the seven double six OS That might imply nice low output ripple and stuff like that. the higher the frequency, it's got lots of current capability. you know, sounds like a good chip, right? And it's available in like a little tiny six pin package.

None of this eight pin rubbish, right that you get with the Seven Double Six. Oh, and so let's actually go down here and have a look. And they did. They actually do give you.

This is one of the ones that actually give you the output ripple. They're actually. you're like right off the bat. look at this.

Fantastic. Now, if you look at this one here right, you can see that output ripple versus input voltage and you get output ripple. I Look at that ten millivolts there down at input voltage. but they don't tell you.

yeah, our out at a hundred milliamps, That's pretty good, right? at a hundred milliamps output current and that might be a killer, right? That might be. It's fantastic compared to some other seven Double Six O-type ones out there, right? So you might think that's fantastic. But here's the trap. Look at this one over here.

Okay, now let's say you're operating at output current of 100 milliamps, right? Quit. One answer? Look, no worries, right? We've got 25 millivolts output ripple. Let's say that's fine for your application, right? But look what happens if you just drop it back? Well, let's say you're operating it like 60 milliamps or something there, right? But let's say that your circuit has different modes of operation. for example, or the temperature changes Because that's why we have three parametric curves here.

That's what parametric curve means. It means you have a different curve for a particular parameter. In this case, the parameter up here is the ambient temperature. So the red one is nominal right? So look, that's 20 milliamps, 30, 40, 50.

So it like 60 milliamps there, right? You get like let's say 70 you're going to be operating at, you know, 25 let's say 25 milli amps peak to peak Ripple But if that temperature changes, Whoa. Look you guys straight up this curve and you're screwed right? Because you're you suddenly drop to another temperature thing, right? It's just nuts. and so you might get one ripple voltage at a particular temperature and then all of a sudden wham changes completely at a different temperature or a different output current. Let's say yes.

Circuit actually has you know, a couple in two different current modes and it takes more current in one mode than the other. The output ripple can like go up like four or five times. Something like that from 20 millivolts up to like 80 or a hundred milli volts peak-to-peak and that could really ruin your day. Unbelievable.

So like. and you don't get that. You don't get this sort of sharp response that we saw over here. Look this output ripple right? It's just.

it's just. you know, pretty linear with your output current because your traditional seven Double 6s just have a single mode of operation and he is The and here's the trick: LM Matt - Double Seven Six has a low current Pfm mode operation, right? So if you search for Pfm Devils in the detail Pfm operation to minimize quiescent current during light load operation, the LM - Double Seven Six allows Pfm or pulse skipping operation. Its pulse frequency modulation by allowing the charge pump to switch less when the output current is less than 40 milliamps. Bingo.

And that's what we saw with that big rise in the the output ripple there because it's it's completely changing modes. There, it's changing frequency. So they do this to minimize the quiescent draw from the power supply and that might be great for your application. You know, if you're really trying to get lower that quiescent current.

But as I said, most of these things are very dependent see user map. They can be very, very efficient. but you've got to pick the right thing. And by the way, the before before I mention at the Seven Double Six Zero, It does have an oscillator pin on here and you can generally either leave that where's the example app Here we go, you can either leave that open or you can put a external capacitor on here to select your operational frequency.

or you can override it by feeding in an external clock. and that's really good if you got like analog to digital converters, sampling systems and you don't want other chips in your system, just especially switching regulators, switching converters, switching inverters, stuff like this a DC to DC converters. you don't want those what running. it's just any frequency you know, higgledy-piggledy bright because that can interfere with a course switching components inside your sampling system.

So often you want to synchronize the clock with your sampling clock and then that can eliminate then your converter. Your ADC can actually do a real good job at eliminating those frequencies. Those switching frequencies out all that aren't noise on the rail so you can often over there. But anyway, the frequency of post operations not limited.

I can drop into the sub one kilohertz range went unloaded and as the load increases frequency and policy and increase in Sun - it transitions to constant frequency operation. There we go. That's what we see there. Wham bam thank you Ma'am Not sure I like it right down here at like really ridiculously low currency can change a lot - even that can ruin your day.

Gone from 80 millivolts might be acceptable in your design because you might be post - regulating this thing. ever using a low dropout regulator or you know, a Zener or even just some. you know, RC or LC filtering or something like that. But you know going from 80 to 120 I could ruin your day.

-. So at light loads see, it's gonna be. you know we're really careful with this thing so you can really come a gutter with a chip like this that has different modes of operation. especially if voltage ripple is important to you.

because look, you get out the top here. Applications: Data Converter Power supplies, right? You might think you might see this you know banner up here. These are always, always almost always kind of thing. They just marketing.

just throw these terms in there and just assay. You know, try and cover all the bases because engineers see you know a lot of them will see this and go, Oh, it's perfect for data converter power supplies. I'm on a winner. I'll use this chip, but of course the kids can have a horrible amount.

an acceptable amount of output. Ripple Audio Amplifier Power supplies. Yeah, that's what you want. Huge amount of ripple on your audio amplifier power supply.

You know it's just like operational amplifier power supplies and stuff like that. So if you've got your negative rail, using this to generate the negative rail, if your power supply and you've got you know, 100 millivolts of switching noise on your negative power supply rail that can ruin your day. Um, because you know your power supply rejection ratio, your Op Amp may not be that great. So there you go.

That's a that's a real trap. These dual mode converter chips just watch out for it. So in this particular case, like because These parametric searches on digit and males aren't that great, this is where One example where you might want to go over to the manufacturers website and use their parametric tools or their product categories. In this case, if you go over to Ti and you're going to power management devices, you know you've got all your little Dioz.

But in the under the switching regulator ones, we do actually have a category down here. We've got a boost charge pump induct Alice and we've got a buck boost or inverting charge pump inductor 'less thirty-four here. So if you go into that category down here, bingo, You get all these chips down here. and of course one of them is our friend of the Lm-2 Double Seven six here, the Switch capacitor inverter And just based on that you might think hey, this one's fantastic.

Its equivalent to a seven double six I/o but it ain't It's got those different modes of operation that you can really come a guts are on. but I Actually like the look of some of these other ones. Check this one out. Low Noise regulated inverter with integrated LD Oh Oh yeah, now we're talking so let's have a look at this bad boy here because one of the things you might want to do, of course you might use this seven Double 600 inverter.

which by the way that it's such a jellybean part the seven double six so that if you go to Aliexpress or something like that, they're available in tons of different Onehunga brands genuine or not doesn't matter in the case of the Seven Double SiC so it's probably not a major risk in terms of getting like you know, counterfeit parts and stuff like that unless they physically don't work at all. because really, the you know, the spread of operation of this thing is in the topology is so sort of wide that you know pretty much any one's going to work the Seven Double six. So especially at like low currents and stuff like that, if you're only drawing a milliamp or something like that, pretty much any Seven Double Six I will probably do the business. but of course it might draw more quiescent Karen It might not be as efficient, whatever, but you know, generally you're going to be okay, but they might have a significant amount of output ripple because you can only do so much it can't put an infinite amount of capacitance on that with that C2 capacitor on the output because at some point the ESR of the capacitance is going to take over.

you're gonna have a a really well a minimum amount of ripple that you can get rid of, right? Learn that you can reduce the ripple to before the ESR of the capacitor starts going up because the higher the capacitance for a given package size means that your ESR must go up. So then it it reduces the effectiveness of reducing that output ripple and as we saw in that complicated formula back there. so there's only so much you can do. you can't just put you know a thousand mic in there and think that your ripples going to zero.

So you may have to do some post regulation. so you might put a low dropout regulator on the output of your seven double SiC So for example, if you need a minimum amount of ripple, but there's a bit of a trap there using a using a seven double six. Oh, and then having your post regulator on there is depending on the voltage drop across that regulator. If you only drop in a small, the smaller voltage you drop, the less effective it becomes of filtering input, noise and stuff like that.

So if you only got a low dropout voltage on it, then your noise might pass mostly through that regulator. so you know you've got to be careful there. It's not a magic put in al do and the outputs not a magic bullet. So let's have a look at this.

bad boy. inverts and regulates the input supply voltage. low output ripple. There it is.

Shutdown. Lowest quiescent current blah blah blah. up to 250 milliamps output current that's huge, right? That's enormous once again. Two megahertz operation high frequency operation so it can get lower output ripple easier.

So I Want to see the block diagram of this bad boy? Where is it? I Come on there it is. double current switched array and then yep, you guessed it, we've got an LD Oh there it is. So yet negative bandgap, low-pass field and they've got a low-pass filter here and voltage out. So there you go.

It's got integrated audio. Awesome! Let's check the price on that, see if it's actually cheaper than this LM 7 + 2 double 7 6. Hmm. no unfortunately it's not cheaper there in 3000 Quantity: We're talking 44 cents here for the 2 double 7 6 and the 2 double 7 6 one with the integrated L do.

It's more expensive, needs greater silicon area. They can't get the yield on the word, not the yield there. You know the density on the wafer so you know your pay for wafer space. So for 3000 quantity 82 cents so you'd have to weigh up that maybe you could get might see.

It might be cheaper to just go with the other one with an external audio that you might get a you know in Japan radio call bill do or something like that and you know, cheapest chips and do that. but once again it may not be as effective. but this - double 7 6 1 I Rather like this, like to have that LDO integrated and what taught what type of pairing data once again powering data converters, interface power supplies, operational amplifier power so you know, just generating a negative rail for your Op ham and stuff like that. Here we go: Output Voltage ripple.

Here's the money shot. This right? We're talking VN at 3 volts and V out minus 1.8 you're gonna get higher ripple at the higher voltage supply if you're going from you know, 5 to negative 5 for example, but that's really quite good. That's under a and under 1 millivolt. There, you'll struggle to get that kind of ripple with an external audio, so that's you.

know it's doing really good. and of course that's going to increase with the increased output current. but even at 250 milliamps anyway like yeah, there's no, you know, weird Pfm operation mode where your output ripple just goes to buggery. duh.

Yeah, neat, But check out this bad boy here now. we just like surfing for parts I did sorry for the tangent, but you know it's just cool I Like this one looks really groovy. look at this generates low noise. Adjustable positive supply between 1.5 and five and negative supply between negative one point, five and five.

So it's actually got dual regulators in here? Yes, Wow Fantastic, right? So for a single five volt in, you get a regulated output so this could potentially replace. Let's go down ever. look at the block diagram. Potentially replace two regulators in your design so you can put all in one chip so you have there so you can consolidate a seven, double six Oh some other positive voltage regulator you're using in your design and the negative filtering audio on the negative rail and the output is seven double Six zero.

So there you go, There you go. It's got two. it's got a positive and negative one and a separate a totally separate positive one here by the looks of it, so that's really groovy. I Like that and unfortunately if you go over in the prior and look at the price, yep you pay a bit more.

Once again it needs more silicon real estate so it's 97 cents in 3000 quanti but hey that could and it seemed like a little pain. the are slammed Qfn type package but you know it's it's not a huge but you might need that. You might need the density right and that could save you space and not potentially cost. You know it might be in via main driving criterias cost.

You know you may not use this part, but the problem with using these specialized parts is that there's one source I bet you you won't find another pin compatible one from another manufacturer with this. So that's the advantage of the seven double six so you can get it jellybean part from anyone available. You know it'll never go and become unavailable really and you can just use some then standard regulators whichever standard pin out. Once again, you've got a wide choice of manufacturers, but you might have demanding requirements like you know, the ability to out like you know, noise pass-through about versus dropout voltage and all that sort of jazz.

But anyway, there you go. T I have some interesting parts in that respect, so you don't Often as a general rule, you don't want to be locked into a specialized part like this if you can avoid it. but you know you may need it because you need the board space or whatever or the size. So they've got some interesting parts in here.

Look at this one. Low Noise Negative Bias generator. Whoa. Well, here's a specialized part for you.

Look at this funky thing. It literally jet like it generates a negative 2 point 3 2 volts. Why 2 point 3? 2. Because you just need often, you just need to be able to go to ground with an Op-amp or some other part so you can't power the part from like 0 to 5 volts.

For example, you can't always get right down to 0 if you can't sense down to 0 or you can't output down to 0. If you have just a small a smidgen below, you know, point one volts below ground, then your circuit can happily sense an output all the way to ground. So often you might just need something like this. You don't need negative 5 volts or negative 3.3 volts, just need negative 0.1 or something like that.

And that's exactly what this chip does with an output ripple of 4 billion volts. peak-to-peak supply voltage of three to five point two five ninety-eight percent conversion because it's just driving bugger. all. That probably only has like ten milliamps tops and it just generates a negative rail.

That's all there. It is loaded at low voltage amplifier for example and true zero output voltage. There it is that actually tells you by generating a negative point to three volt rail and that's all you need. So that's a nice little specialized part there.

Geez, how much does that cost? There you go. 33 cents in 3000 quantity, so that might do the business there. But once again, that's not going. Is that a A compatible A pin compatible to seven double 600 for goodness sake.

Like, just put them. put the labels directly on here, not pin one through the pin 8. Have a table. Just just put that lazy ass.

whoever did this datasheet. Anyway, is that VSS ground pin - no, that's not a Seven Double 600 compatible pin out. I Don't think so. Yeah, you might be stuck there if you decide to I use that part.

But isn't it neat? So there you go anyway. I've ruffled on enough. Sorry about that. I Just I Started out just wanting to show this trap here and it might look obvious.

You know it might look real. it. Look well there it is. The first graph in the datasheet shows you that, but you know if you're not paying attention, you look at this one or you know you.

Whatever reason, you didn't notice this or didn't think about the changing mode of operation in this chip and what effect it can have on voltage ripple. especially if you're doing the famed data converter, power supply or audio amplifier power supplies. Where Ripple is almost certainly important, you can really come a guts up. Anyway, there you go Traps for young players modes and chips? Geez, no, what's your effort? Oh, by the way I just thought I'd show my own product I don't do it very often so I please forgive me.

but it's kind of relevant. Um, the micro sleeves. The micro sleeves are back in stock I have to link in the video at the end of this if you haven't seen the Micra sleeve and it's a neat way just to hold your parts in aesthetic static protective thing. You can just slide your parts in there, label them all and it's just a real handy way to do it.

Yeah, it's just a really cool way to organize all your our parts for a particular project so you might have a folder like this for a particular product. In this case, we've got like schematics and other of our stuff in here evening but I want to show you that for him and got my waffle trays and other that's taped inside here so it's quite handy. It didn't haven't been stopped for a while, but they back over on the website so I'll link it in down below. Check it out Anyway, if you liked that video, give it a thumbs up.

As always, discuss it down below and as always you can support me on Patreon. I Often release videos early on Patreon so that's linked down below as well. Catch you next time you.