Hi Welcome to the Eev blog an Electronics Engineering Video Blog of interest to anyone involved in electronics design. I'm your host Dave Jones Hi Someone mentioned a while back that I should do a Blog on choosing a part or how I go about choosing a part for a typical circuit now. I've touched on this before with the design marry, go around using Digi key and everything else and parametric search engines to find suitable Parts but can I do one in detail? Well, that sounds like a good idea and it just so happens. And I'm working on a small little project at the moment where I think this might be an ideal example.

So let's see if we can do go through the process of choosing selecting a suitable part for a single cell. DC Todc Boost Converter The first thing you do is take a look at your basic requirements and in this case it doesn't matter what the product is. Let's just say I want to power my circuit from a single cell a single alkaline able a AAA cell 1.5 Vol cell that you're familiar with. So I need a boost converter and in this case I want to convert it to 5 Vols at a maximum of half an amp so that is 2.5 watts of output power.

It doesn't sound like much V * I Okay, 2 and 1/2 Watts doesn't sound like much, but to get it from a single cell might be a bit tricky. Now you've seen this circuit before. It's a basic Uh boost converter circuit that I went through in the DC to DC converter tutorial. So I won't go through it again.

But the basic concept is that it has a Fet here which stores energy in the inductor and then the inductor dumps the energy into the output capacitor and that forms a basic boost converter. And this fet here is actually a Uh chip. It's like a single chip solution and that's what we're going to look for today. We're going to try and select, see if we can find out of all the millions of chips out there a chip that just does this job here for a boost converter.

Now because it's a single cell. Okay, the input voltage is going to vary from .8 Vols to 1.5 volts. Why does it do that? Well, if you look at the Uh characteristic discharge curve of a typical alkaline cell, it looks something like this. This is voltage of the cell versus time or or actual discharge time in minutes or hours or days or something like that depending on the current and I'll have to do a separate blog on this and I will.

But basically, uh, the input voltage starts out at 1.5 volt and then it. it diminishes in kind. once it after this little drop at the start, it's kind of sort of linear, probably down to around about a volt and that's where most of the energy in the battery under that curve is used. But you might want to go down to say8 Vols which is deemed to be the typical cut off uh point for a an A typical alkaline cell and that's where most of the energy is used.

So if you want to get an extra 10 or 20% energy out of it or something like that, you can see after about 8 volts, it just drops off completely. So IDE So your ideal chip for a single cell? Uh, DC Todc Boost Converter is to have an input range from 0.8 Vol to 1.5 Vols And in this case, we need 2.5 W of output power. Now, as you'll see when we go through selecting a device in much more detail, let's do a basic calculation of how much switching current we need because uh, these DC Todc Boost converters are typically rated by their switch Peak Switch Current capability. Now 0.5 amps on the output.

Okay, 5 Vols at 0.5 amps doesn't mean that our chip needs to be capable of5 amp switching current. No, because this is a boost converter, The the input current which goes through here and down through the switch is much much higher than that 0.5 amps. and that is going to have a direct relationship to the input voltage Because we've got a very low input voltage here of 0.8 volts and we want 5 Vols that's out. That's quite a step up.

So therefore, this input or switching current down here is going to be much greater than our output current of 0.5 amps. So it's going to be rough. Here it is I switch. Okay, isw is approximately equal I Won't go into further details, but this is a rough rule of thumb.

You can use V out on V in 5 Vols on take our minimum 0.8 Vols times our output current of half an amp is going to be approximately 3.1 amps or higher. possibly. Or maybe if we want only a 1V cut off down here, then we could be looking at you put one volt into here and you're looking at 2 1/2 amps. So we're looking at probably 2.5 amps switching current capability in our DC Todc converter.

Remember that for later. Now, if you look at the converters out there, there's probably thousands of different types of DC Todc converters. A lot of them operate at low voltage, so we should have no real problem finding a converter, right? And what are the other requirements? You got to think about those as well, and it's just so happens. I Have a quick list here.

This is just a basic list. It's not complete by any means, but these are some of the things you might want to think about if you're choosing a DC to DC converter like this. First of all, number one by far is the efficiency versus the load current graph, which we'll go into great detail on. And you got to be careful that it's at 5 Vols cuz they'll have different curves for this in the data sheet for different Uh output voltages.

trap for young players. Big One: The minimum input voltage of course, very important. tick. We need that cuz we need to go down to at least a volt.

Maybe get away with 1.1 volts minimum input voltage I Don't know, but that's very important so we have to care about that one. It's going to be one of our top requirements. the minimum startup voltage because while the chip might go down to say 0.8 Vols might operate down to that, it might not start up at that. So if your battery is very low and and you try to start up your circuit, boom, it may not do it and that will change with the load as well.

so that might be important in this case for my particular project. Not that important cuz I Expect to start up the battery at 1.5 volts and then just continuously drain it all the way down. But for your uh particular requirements, it may be a big deal. Cost availability always an issue.

Can you get the damn thing? Is it a 40e lead time time? Is it 20 bucks a chip? or is it $2 or 20 C a chip? It matters. Um, the component count because these DC to DC converters. some will have a built-in switch of built-in fed switch, some will have a built-in diode and that minimizes the number of external components you got to have. so that might come into account here.

Um, what's the shutdown current? Because it's battery operated? Do you want to just be able to switch this thing off and then the battery can last for a year or 5 years in standby, so that might be important as well. Uh, what's the footprint size? Is it a big monster footprint? Is it hard to solder? Do you need to hand solder it? Uh, what frequency does it? And what frequency do does it operate and that goes into the size of the inductor you need? No point having a little tiny little DC to DC converter chip if you need a massive, big, huge, whopping and expensive inductor. So frequency and and overall footprint size. not just the chip.

Um, does it have a power good output? I Don't know that might be important. And do you want to know if your DC to DC converter is powered up properly or not and and actually regulating the output voltage? The noise. The switching noise. is that important for my application? No, not really.

Uh, the reference voltage stability over temperature. Is that a problem? My one: I Don't really care that much. It's not that critical, but for your application, it might. uh.

transient response. Do you have big loads going boom boom boom. You know, in and out? that could be important and that's not the end of the list. So there you go.

There's a lot to think about that's just one component in our entire design just for the power supply. It's unbelievable and you have to go through through similar things in your design cycle for other, um, for all the well, a lot of the other components in your design as well. It's crazy. Okay, here we go Now how do we find a part like this? DC to DC Converter Well, I've mentioned this before.

it's to use what's called a parametric search now. Uh, all most of the manufacturer websites will have parametric search, but because we don't know which manufacturer we want to use at the moment, we're going to use one of the component suppliers like Digi key here. So I've opened up the digi Key website and we're going to search for our DC to DC converter. Now let's try it.

DC Let's try it DC converter and let's see what we get Here We go. Now it's under integrated Circuits down here and typically you can tell what you want because it'll have the most number. In this case, 177,000 items down here. Switch in DC to DC converters.

That's what we want so we'll click on that. and here we are inside our DC Todc converter parametric search. Now we can scroll across like this and you can see all the parameters. We've got things like pack packaging, package case mounting type, operating temp, power output which we'll be using because we know we want 1.2 uh, 2.5 Watts if if you remember that from the calculations so we can choose those voltage inputs.

Very important. So we'll be using that one switching frequency not so much. We're not caring too much about the efficiency at the moment except for the fact that obviously we want uh, the device to have as higher efficiency as as possible because then there's uh, that minimizes the waste from our battery. Our current output will'll be using our voltage output.

We might be using that, but because most of these DC Todc converters are adjustable, we might not, um, touch the output number of outputs. We only need one, whether or not we want in an internal fet switch. Here, we might use that. Uh, the type of converter will definitely be using and the manufacturer.

Now here's a tip: if you don't know who manufacturers are various devices and you can use a supplier like this to find like, which manufacturers we actually that actually manufacture these type of converters. So as you can see: Analog Devices Very Dodes Inc Um XR Fairchild Free Scale they're all there. all the big names linear, Tech Maxim Micel, Microchip, Nat Semi on Semi Nxp, etc etc. they're all there and these are Texas Instruments and these are the ones we can go to to use this list to go to the individual manufacturer website.

But let's get down to it now because we know that we want to uh, only look at um, a boost converter. We want a step up here. it is Step Up Boost Converter. We're not worried about cuck or fly back I won't go into those.

We just want a standard Step Up Boost converter. So we select that and we go apply filter and Bingo! It is now only showing all of these manufacturers who manufacture boost converters and it's um, we we're using this to eventually narrow down to the part we want. Now let's go for, uh, the output power shall we? Because we know we want 2.5 uh Watts Basically now we could go uh, current output like this. We could actually scroll down here and um, but current output is a bit deceptive because and because as I said, you don't know, um, these chips are designed for over a very wide input voltage range so the output current might.

It might be able to deliver 2.5 amps for example, but it might be might not be able to do that at a very low input voltage and we'll go into that. We'll find out all that sort of stuff from the data sheets later. So let's clear that we we don't want that item there and we only want to look at power output. Let's see what chips are available in our power output range.

Let's let's be generous and go 1 and 1/2 Watts you can hold down the shift key and let's go up to well. 3.3 Watts that's the maximum okay apply filter and we found um, it's selected 166 items across seven pages. Now we can narrow them down to in stock, but I'm not too fuss if they're in stock at Digi key or not at this particular uh stage. Now what we the other thing we need to do is the voltage input.

There's no point selecting a chip that only has a minimum of say 2.3 volts input like that. That's of no use to us at all. We want one that at least goes down to 1 Vol or lower. So we're going to Select 1 to five.

There's these whole bunch of these ones up here, so adjustable down to points. 7. This one goes down to. 3 Wow, you know that's pretty incredible.

So we'll choose those and we'll ignore all the rest. so we'll apply filter and what have we found? We've got now 95 items down here. I'm fairly happy with that at the moment as a first pass and you can see our manufacturers have dropped. We've only got linear Tech Maxum on semi and Texas Instruments Here are available manufacturers but I know other ones might be able to do it as well.

Let's go into our view page shall we and have a look down here now. Didi Key Have a sort by Price option because price is always. You know price is always an option when you want to do these sort of things so we can sort from lowest to highest in um, ascending order. We won't worry about in stock, but let's get the one-off price, shall we? So sort by Price ascending oneoff price and it reorders it like that: $2 This first one up here, there's $1,000 available $2.98 in one off quantity.

That's quite reasonable. and it's a TPS it's a Texas Instruments Part I Don't mind their parts at all. It's a TPS 61028 device. Um, that one certainly rings a bell and uh, it's got an output current of up to 800 milliamps.

but we'll go into that now. the switching frequency. We're not too worried about the moment, but the higher the switching frequency, the greater the well, the smaller the inductor you need because that's important as well. This design is, um, going to be fairly small.

so uh, a higher frequency giving us a smaller inductor uh will help a lot. now. the maximum power output's only 2.05 Watts here. But I'm going to give this device a go.

I'm not too fussed about the packaging um for this particular project. So let's go in and check out this device. Here it is here. let's have a look at the data sheet and here we go.

We've got the This Ti devices part open and once, which is, uh, fairly common for a lot of these devices. As you can see, it's the same data sheet for many different types of chips, so when you're looking through the data sheet, just keep that in mind that uh, these devices are different and they will have different graphs in there. They'll have different parameters and specs and all sorts of things, so just be careful about what actual part number you are referring to. Now this one sounds pretty good.

96% efficient Synchronous boost converter 96% right? Sounds very impressive, but we'll go into the detail, shall we? Um Device: Quiescent Current: I'm not too fussed about how much Um current it takes during actual operation, not too fuss. Input voltage range: no.9 volts great, Not a problem. I'm fairly happy. doesn't go down to 08, but hey, I'm fairly happy with 09 anything one or under I'm fairly happy with uh, fixed and adjustable output options.

That's that's great. We might be able to get a fixed output voltage option which allows us to, um, minimize to, uh, lower our component count. We don't need these two external voltage set resistors which you'll typically use Um applications. One cell.

There you go. it's it's specifically designed for one cell, two cell, three cell alkaline. So let's see how good this puppy is. Now as you can see, this is an example circuit here.

and uh, there's one thing you'll notice missing from this circuit. Where's the diode? It's not there, so it must actually be built in. So this one's fairly handy in that it actually, um, with a built-in diet that lowers your parts count and lowers your component cost. So that's that is definitely a good thing.

So let's scroll down here. and really, when we when we're looking at a DC to DC converter like this, we really want to go down to the guts of it. Which are the graphs. Okay, so we'll scroll down.

this is the internal operation of it. but we'll scroll down and we will get the characteristic curves. Let's find them. Now what we want is Aha.

Now we're now. we're looking at it. We want the efficiency in percentage um on the Y axis there versus the output current milliamps on the X-axis Now as you can see, um, this is for the TPS 61 O20 and Vbat Okay, is 0.9 Vols and that's what we want. 0.9 volts.

As you can see 85% efficiency down at 1 milliamp. Really nice. It goes up. but look 100 milliamps? Okay, it's still 85% efficient.

Awesome. Pretty happy with that. but then it tails off like this. and at 200 milliamps um, output voltage? Ah no look, we've been fooled.

Oh d look V out equal 1.8 Vols Okay, Ah I've been fooled again. I Do it every time and this is a real trap for young players. These these characteristic curves are only for V out of 1.8 Vols that me. So these have no relationship at all to what we want.

We want 5 volts output. So what we need to do um is find a characteristic curve graph. But let's look at this graph over here on the left hand side: maximum output current versus input voltage. Perfect.

Okay, our input voltage 0.9 volts down here. our vout 5 Vols It's got multiple graph superimposed. So let's look at the 5V V out graph here and it plummets down like that. So at 0.9 input at 0.9 volts input on out for a 5V output, it's only going to do about 100 milliamps Maybe 50 milliamps or at 1 volt input it might squeeze up to 200 milliamps output.

But look this chips of failure right there. We simply can't use it. Now just to prove that. Uh, let's go down and find an efficiency graph for 5 Vols out because it will have continue to have these graphs here we go that's 3.3 and Bingo! here's V out equals 5 Vols for various input Uh voltage levels.

Now as you can see when the input voltage over here the the higher the input voltage, the more output current you can get. Look at this if the vbat here is 3.6 volts over here. If your battery voltage is 3.6 you can go up to 1 amp output current Huge! Okay, 5 volts, 1 amps. That's 5 watts and it still does 90% efficiency.

It's awesome, but the trick is for these low voltage converters. Once you go down, you're looking at this graph here which which then tails off completely at 250 milliamp 100 down here 2 200 at about 250. There it is. it's tailed off completely.

so this thing is useless and that's just going to continue to Plum it to to nothing right down here. So we we'd be lucky to get 300 milliamps out of that at V at a 1.2 volt input voltage. but we want to go down to 1 Volt or lower so this device clearly is not capable of that. Okay, so that TI part's a faure.

Well let's go back. The good thing about this is that you can hit the back button here and it goes back to the list and you can hit the back button again and it goes back to your parametric search. uh, search you had before and you can just go forward and back and it actually keeps all that info there. But let's look at these other devices.

We've looked at the Texas Instruments Now let's look at a maximum uh 1947. let's take a look look at that one. Let's open up the data sheet here. Okay, low input output voltage: Step Up DC to Diesa converter with reset sounds pretty good.

Low input voltage: 0.7 volts. Uh, high 94% efficiency sounds pretty good. Fixed output voltages: 3.3 Well, um, hopefully it'll go up to five, but no look at it. These devices only go up to 3.3 So this device is a fire straight away and we could have fixed that by uh, sorting our parametric search by output voltage as well.

But we'll We'll just live with that for the time being now. I've done looking at the Ti Parts I Want something else? All right? I Found a linear technology part here LTC 3424 I've heard of that one before, so let's check it out. Oh 3 MHz Frequency operation 2 amps um, output current sounds sounds great 1 5 Watts not quite there, but hey, let's um, because I can overdrive this the uh, there's a little Quirk with this design where it really doesn't matter. Um, if I overdrive it or something like that I'm not too fuss.

So let's go into the LTC 3424. It's a non-stock part, but that's not going to stop us. We might be able to get it somewhere else and let's take a look at the data sheet, shall we? 3 MHz that is a very high frequency. uh.

boost converter indeed. 1.5 Vols to 5.5 output voltage Excellent. 1 amp switch current. Uh, well, where we're going to need at least the 2 Amp switch current there for the 3424.

Um, but we might be able to overdrive. It's not a problem. Wide input voltage range .5 volts. Excellent.

Great, but what do we want to look at? Give us the efficiency graphs. Okay, now let's have a look down here. The efficiency is. These ones down here are for a V out of 1.8 Vols That's hopeless.

A V out of 1.8 Ah, look over here on the left hand side. look at the circuit here. This one has two different input voltages. Notice how pin six is a Vdd pin there and that goes to a higher voltage from 2.7 to 5.5 So this isn't a true single cell device.

It actually needs a second. Um Step Up converter to: uh, step up our single cell just to drive the Vdd or the chip and well, that's a bit of a showstopper. Um, well, not so much a showstopper. We might have to resort to using this device.

so let's let's not count it out yet. Let's go check out the input graph. Uh, the efficiency graph. Sorry, let's go and find it For Efficiency Graph Converter: 1 .2 to 1.8 No, we want 5 Vols give us the 5V converter graph.

It doesn't have one. Look at that. No, it doesn't have a 5V output graph so that's pretty useless. This device, no, doesn't have a parametric curves for 5V output.

Not impressed at all. So I'm going to rule this one out because it just doesn't have the information that's easily got um from the graphs because we want to know the typical performance of this thing. Um, and quite frankly, if it doesn't have a parametric graph, I'm not going to use it I might use it as a last resort if I have to go in there and calculate it or measure it. but I don't want to do that right now.

I'm looking for devices now. Let's check out a maximum device down here Maxum 1765 Let's open the data sheet. Okay, now this maximum device is only an 800 milliamp Step Up DC to DC converter. But it's got a 500 milliamp linear regulator, so who knows this might be good.

Um, adjustable output from 2.5 to 5.5 up to 800 milliamps output? Uh, let's have a look at its parametric graph. Okay, here we go. Efficiency versus load current for V out the one in the middle here. Uh, V out + 5 Vols Now let's take a look.

VN at 1.2 Now it has different modes of operation. You can see here that, um, there's actually a normal mode and there's a Pwm mode as well. So uh, the basically the normal mode modes. They will allow greater efficiency at very low or almost no load currents.

but um, I don't need that for my circuit I just need it to work in Pwm mode at a fairly High You know, a couple hundred milliamps up to the 500 milliamp maximum. So we're looking at those black curves there and we're looking at VN equals uh, plus 1.2 Vols Now, uh, the load current we're looking at here is uh now I'm looking at these graphs here and something doesn't seem right. this one. Efficiency versus load current for V out 5 Vols This is what we want Now this is these are the typical characteristic curves you get.

but look at this for VN 1.2 Vols It's saying it's this bottom curve here and if we follow that curve up, it shows that it's this big one which goes right out here to about or 800 milliamps. That's crazy. It seems almost as if it's back to front and this: VN at plus 3.6 Vols Back here is this curve here and it cuts out there. at 200 milliamps output current, it's back to front I Reckon they've screwed that up if we look at the one on the right on the left hand side here.

Efficiency versus load currents. Exactly the same parametric graph, but for plus 3.3 Vols out. Look, this is is what you'd expect: VN at plus 1.2 is this graph the bottom one here which comes short and stops short like that? That's what you'd expect and you'd expect the same thing over here on this. Uh, on this graph on the right here.

but I think they've actually this is a data sheet mistake I Believe it is. They've actually labeled this one down the bottom here. that label down there should be + 1.2 and this one in the middle. They've got right at 2..

For and this one here that it extends all the way out to 700 milliamps or so should be plus 3.6 Vols Ah Ah. Maxim You've got your damn graph wrong. But these are the things you've got to watch out for. So that's a real interesting dilemma.

if you didn't have the experience to know that, uh, what these graphs should typically do and know what to expect from them. And you read straight off this graph, you'd be reading the wrong data and you're designing that part into your prototype and the damn thing wouldn't work. So data sheets are not infallible. You've got to watch out for him.

And in this case, the good thing is we have another the same graph here on the uh, left hand side. exactly the same uh parametric result here. and look. efficiency in percent.

They've got 1% up here from zero to one. It's crazy what's going on here That's hilarious. It looks like Maxim have completely screwed up this data sheet. totally ballsed it up.

But these sort of things happen and you got to keep your wits about you and you've got to, uh, know what to expect from these things. Don't take the data at face value. Always ask yourself, is this the expected result? Are these graphs what you would expect? How do they compare with other manufacturers, data sheets, and so forth? And a dead giveaway that they've actually got it wrong is as you can see, it's this: one is labeled V in Plus 1.2 Vols and it overlays with this particular graph here. So if you go down there, they've they've clearly labeled it incorrectly.

CU These are supposed to match up at the high end and deviate at the low end, so the labels are a clear giveaway that's incorrect. Back here at our parametric search page, we've got one device down here right down the bottom from ON Semiconductor I Really like on Semi, so let's check out their part the NCP 4 22. Let's go in, call for the price. It doesn't give you the price at all, but that's not going to stop us.

Let's take a look at the data sheet and see what this Baby's Got And here it is 800 milliamps Synchronous Rectify But as I said, you can't take that 800 milliamps at face value Because okay, we need 500 milliamps on our output and you think this one will balls it in easy with 800 milliamps? Well, I think we'll find that. That's not the case. Now let's go down and try and find the parametric graph again. And here we go.

We found the efficiency versus load current Exactly what we want. Now we want the output voltage. This is the one on the right hand side. Here is V out equal 3.3 That's not the graph we want.

We want this one V out equal 5 Vol And notice also that they actually give you the uh, typical values that these will measured at. So it gives you an inductance value of 6.8 microen, C in and C out values as well. So these parametric graphs will change with all of your circuit parameters as well. so you we're really only taking taking these as a guide at this stage a rough you know, ballpark, um uh, type thing to see if we can use this device, but it will actually require either further calculation.

Further, looking into the um, the parameters of the data sheet and building up the Prototype and actually measuring it before we can actually make a call on any individual device. Now this one only has a VIN of 1.5 Vols So really, that's not helping us much. Now if we go down here, there's a V out equal 1.8 with a V in of 1.2 but they don't have really the uh, the the curve we want on this characteristic graph. We' I'd like to see it down at 1.2 Vols or or 1 Volt or even lower.

what does it actually do? But so we're stuck with the 1.5 But even at the 1.5 look uh, it's only going to do 100 200, it's only going to do 300 milliamps at 5 volts at 1.5 Vols And you know that it's actually going to be worse than that. At lower voltages, you'll have a curve that'll go something like that and then drop off much earlier at 1.2 So this one's a clear loser. So we've exhausted the parts we found on our first pass here for Digi key. Now let's actually go back.

We'll scroll back through these parametric uh search and we'll take out the uh the power output which we had cuz sometimes they don't specified. Okay, the power output here is not specified at all, so we'll actually reset that. Now let's go for say, the output current. Let's try and use this as a search parameter, shall we? Now now, this is a trap because as I said, if you thought that the output current was only 500 milliamps capable, then really, you know you're not going to find the devices you want in that region cuz the switch current curent uh is going to have to be much larger than that.

but let's choose 500 milliamps anyway. No, actually we we'll start at 1 amp and we'll go up to say 10 amps. That's pretty extreme, but let's try it out. Apply filter and Bingo! have searched and once again, the voltage input is a really key requirement, so we must have that.

But let's stretch it a little bit. Let's stretch it and say VN 1.2 Vols Say let's let's be fairly generous because it might operate a bit below that. The parametric search data could be wrong. You don't know.

So let's narrow that down and Bingo. look at the manufacturers. We' got diodes Inc we've got Mel I like Mikil Parts Um, we've got TX semiconductors, some of the smaller players sech. so let's take a look at those parts.

There's 173 items down there and let's go into view page and once again, we'll sort by Price shall we? Price is always a good indicator to Uh search and to do a first pass search on. So as you can see $135 each in oneoff quantity. So they're going to be really cheap and these are tiny little devices. Look at this: Torx device down here.

Um, it's got a 1 amp um output capability anywhere from Uh 1.8 Vol to 5.3 Vols output 8 Vols to 6 Vols In Let's take a look at this. let's see what Torx can do. The good thing about Digi key is that it just allows you to jump straight to the data sheets and you don't have to go to the manufacturer's website. Bingo they pop open when I was a boy.

you had to have you know bookshelves full of these data books and they're the only devices you could use. But anyway, let's not go there. Let's see what this TX device has to do now. Output Current Oh no, we don't want that bit of a fail there there.

Okay, now down here it shows that we've got 500 milliamps output it's capable of at output of 3.3 Vols at a V in of 1.8 Uh, it's really not going to do it. Um, because we just know from experience looking at the other graphs that it just gets worse with a a lower input voltage and B a higher output voltage that differential between V in and V out. When that gets wider, you know the current capability is going to drop. That's why why, um, we failed again.

That's why this one here that has when VN drops to .9 Vols and it's got a greater Vin Tov out range. The max output current is only 150 milliamps, so that's no good at all. But let's go have a look at the characteristic curves anyway. Output voltage: 3 volts Oh no, we're it's no.

let's not bother this sucker. just not going to do the job. So we're back at our Digi key search here. and well, that price thing didn't work out.

Let's search by output current, shall we? Uh, here it is output current. uh column. Let's sort downwards. so descend in order Max output current of 5 amp.

Now we're talking right. linear technology. Look, this looks like a big pin count uh package. So it's probably a uh, multi-channel converter or something like that, but it's input volage .5 Um, so let's go check that one out, shall we? It's $536 cents for one off which I guess isn't too bad LTC 3425 And yes, I was right.

It's a four-phase synchronous Step Up converter, so that means it needs four inductors if we go down here to the Circuit there it is four different inductors so that takes up a lot of board space, but that will definitely get you. Um, the extra the the. The effic efficiency is much better with these multiphase devices, so you might have to sacrifice board space for uh output Uh current capability. So let's keep this one in mind even though I don't have much board space.

I'm going to keep an open mind and this one is for a V out of 3.3 so no I don't like that at all. Let's go down and find Bang. As you can see, we ignore all this, all of this data. here, all these specs, we just ignore them and we go straight to the bottom line of the efficiency graph.

Here we go: Converter efficiency for V out at 5 Vol And as you can see V in Ah, look, it only gives you a minimum V in of 2.4 That's useless I Want to go down to 1 Vol So it looks like this thing just doesn't give us the data that we want V out at 5 Vols discontinuous mode forc mode oh gets all messy um and uh. converter input current microamps no let's no, it just it's not really going to have what we want. Ah, so let's this is another one which another graph we can get the maximum output current in uh Burst Mode operation V out equals 5 Vols at versus V in output current V in and as you can see at 5 Vols at VN of 1 volt, it only does 50 milliamps God What a wimp! And let's just keep going through the list because this is What you have to do typically to find devices like this. You might get one that you like first go, but this is a bit more of an obscure application.

To go from a true single cell up to a 5 Vol output at Uh 2 1/2 watts is actually quite a demanding application. So let's check out this. LM 2623 Let's look at the data sheet: general Purpose Gated oscillated DC DC Converter Boom I Don't care. Let's go down to the parametric graph and this one, as you can see, needs an external diode on it.

Let's go down and try and find these graphs. Here we go: Efficiency versus V in exactly what we want for V out 5 Vols Bingo No problems at all. V In Ah, as you can see, these graphs do change manufacturer to manufacturer. they're not always the same.

This is actually Uh versus VN So this one at 600 milliamps. It doesn't really have the 500 milliamps we want, but we can sort of guess that the 500 milliamps is sort of going to be well there. There's the 300 milliamp one. So and that's the 600.

so you can guess 500. Let's just split it down the middle like that and say 500 goes down there like that. And the problem is with this device, it only has goes down V in of 1.8 So that's no good at all. This graph? you? You don't know whether or not these things just gently go down like that or whether they tail off really quickly.

So in in the case of the 600 milliamp, you can see it really tails off very quickly and that's just going to Plum it like that. So really, this one doesn't have the graph we need to uh to determine if this device is suitable or not. So this one's scrapped too. All right, I'm sick of using Digi it just hasn't produced what I want in this particular instance, so let's choose one of those manufacturers.

TI Uh makes some really good converters. So let's go to the Ti website and let's go down here to the power management. There it is and Bingo! let's try and this list over here. Different types of switch in Regulators As you can see.

Step down, step up. there's 90 of them. They have 90 different Step Up Regulators Surely we can find a regulator in here from 90 of them. Oh, check this out.

The good thing about Texas Instruments Look at this. They have a specific checkbox for one cell. uh, sorry, one cell alkaline nickel metal hydride input. so let's tick that they're doing their hard work for us.

It automatically refreshes the table. We don't have to do anything else. Look, we can type in the input voltage here and do better. Better parametric search, but let's search for a true one cell capable um.

alkaline converter and Bingo! these are the ones we've got here. The TPS 61026. That's what we looked at before originally. Here it is.

You remember this, the Uh Texas Instruments data sheet. We had the 61026 so it looks like that's pretty much the only device. Um, they've got that will actually do it. There's another one here, the TPS 6122 uh series.

which is that part of this one over here? 22? No. So we can, probably, um, take a look at this one. and here it is. We've got the TPS 6122 and let's take a look at the data sheet.

Let's not muck around waiting for the internet can be a real. There we go and we're up right I Don't care about the rest of the crap up the top, just give me the graph. That's all I want Really? Oh, efficiency versus output, current and input voltage. Oh, check out this.

It's even in color. Isn't that neat? Let's see if we can make heads or tails out of this one. Now the input voltage up here. it does go to8 so that's brilliant I Love that.

But this. ah look. there's the trap trap for young players V out 3.3 Vols That's no good at all. Let's see if we can find the graph down here.

similar one for the 5 Vols which is what we want V out 1.8 Here we go. we've got it. Efficiency and versus output, current and input voltage. Okay, now we're talking VN of7 volts.

Excellent. Ah, this is a real wimpy device. Look at this. it's got output current at 7 volts only goes to H 25 milliamps useless.

No, this really isn't going to cut it. even at a V of 1.2 We're only talking No, we're we're talking sub 100 milliamps useless. Scrapped. All right.

So we've done our dash at TI Let's check out Microchip, shall we? Because microchip are highly underrated when they come when it comes to analog. Uh, Parts I've mentioned this before, they're very, very cheap and they're really quite good performance. So let's check out their power management. One's down here.

we're switching Regulators Microchip. Here we go. It jumps up with the parametric table. really nice.

Now what we want is input voltage range here. So we want to sort here from low to high. So there we go. They do make ones.

It looks like they only make uh, the mCP 16, uh, 1623, 1624, and 16 1640 range which goes down to a low enough voltage for our particular use. Uh, now let's check out the output current milliamps. Well, this one only goes to 350. That's the beefiest one they've got.

But uh, let's check it out anyway, just for fun. And let's load up the data sheet and here we go: the MC P640 It's quite a nice device. It's only a small footprint and typical converter for 3.3 Vols out n give us the real graph I want 5 Vols Thank you Okay here we go: 5 Vols out Pfm or Pwm mode. As we've mentioned before, uh, Pfm mode allows you greater efficiency at lower current.

So we're looking at the dashed Pwm only mode here: VN at 1.2 is the lower graph, it goes up and starts to drop off and the graph ends at about 100 milliamps for 5 Vols out. So we're about five times short. Oh well, and let's try National Semiconductor cuz they're big in the Uh converter market. So let's go down and have a look at their boost converters down here.

Convenient link on the front page here and they've got this like Java sort of app which I don't know, don't really don't really like it. It's a bit of a bit of a pain in the ass, but here we go: Minimum input voltage Okay, we're looking at one point. let's change the slider here at it's a bit tricky, but let's go to 0.99 Actually, let's be generous. let's type it in 1.2 Let's hit go and look, they've only got two devices LM 2621 and Lm26 23 so that's no good at all.

We've already looked at the LM 2623 that's the best they had and it wasn't suitable and we can't stop there. Let's try linear technology. They make some of the best devices in the business so let's go to Power Management. Let's go to Switch In Regulators Let's go to Step Up Regulators and let's see what they can do for us.

Let's go down here. Let's not worry about all this quick search I don't really like the uh linear Tech thing they've got down here. It's a bit confusing. Let's go to view all products view table down here and we'll sort it out for ourselves.

rather than use their silly little tool. we'll go V in minimum. Okay, so we're looking at um, let's sort that column there, the Ving column and as you can see, they've got quite a few devices which go down to 1 point2 volts here. The look at them.

there's a whole bunch of them so we're going to have to check these out. But let's also look at the switch current. Now let's uh, look at the switch currents for well, 180 amps is just insane. But let's go for say anywhere from say 1 and2 amps to there.

So let's update that and Bingo! We still got a ton of devices which actually oh sorry, no, we have to go uh V in minimum so let's go V in 1.2 It It cleared the previous uh thing we had and Bingo! We've narrowed down our devices to these ones here now. Now let's take a look at uh, they all do Vin minimum 1 Vol that might be good enough V out uh Vin Max 10 switch current 3 amps that's what we're talking about. Um, so in an S8 package, let's take a look at the LT 1308 and here you go: 5 Vols at 1 amp from a single lithium ion cell. Now we're talking.

we've only got an alkaline uh cell, so maybe it won't do the 500 milliamps whereafter. But hey, this is this. Sounds like it might certainly might be in the ballark. So let's open up the data sheet.

Okay, let's not Mark around. Let's go straight down to the graph, which is what we want. although they've got one here for it. doesn't tell you what the vout is.

No, doesn't tell you on that graph. What's the point of that? If they don't tell you what the V out voltage is crazy? Well I can't see it there. I must be blind. Anyway, let's go down and find the proper graph down.

here. Here we go: 5 Vols Output Efficiency Let's take a look at this baby. What can what can it do for us? 1.5 volts input voltage. Ah, it drops out at 100 200, 250 milliamps What fail and that looks like that was the best device that Linear Technology had.

Because if you go back and look at the why do I have to click resin there It's crazy if you look at the ones that we had that had the biggest uh switch current capability So that's going to be the best device out of all these. these ones won't be able to touch it. but if you want to go, we can look at the 3539 just as a quick little aside. but you know, because the switch current isn't as large that it's pretty much not going to do it.

But hey, it might be a little bit more optimized. So let's give it the beneit benefit of the doubt, shall we? And we'll go down here in the efficiency: low current at V out 1.8 3.3 there must be another one here. 5 Vols There it is, our friend. the 5vt efficiency versus low current graph.

Now for V in, it's only got Vin of 2.4 Once again, that's a fail because it doesn't. um give us any data that we can use to actually uh to see if this device is suitable at um, you know, at Uh at low input voltages. So the efficiency here at V in 2.4 at 2.4 Vols Yeah, it doesn't amp, but what does it do here I Don't want to have to buy the chip, build it up, and then actually measure these graphs myself. What a pain in the ass.

So I'm going to give Linear Technology the flick. Well, we're starting to get a bit slim pickings now, but let's go to Maximum and see what Maxum have you know about Maxim's lead times? I've bitched about them before and their availability, but they do make a hell of a lot of Uh devices. and they make a hell of a lot of Uh Power regulators and switching converters and stuff like that. So let's go into Power and Battery management.

They make 1769 different power management devices. It's crazy and this is one of the problems. Why Maxim can't actually Supply their devices because they don't have enough factories to churn out the things cuz they've got. you know, 20,000 different parts or something.

It's crazy. Anyway, rant over DC to DC switching Regulators step up. there's 89. They make 89 different Step Up converter chips and that's fantastic for us.

So let's go in V in minimum. Ah, here we go. and this is I like Maxim because as you can see as I slide this um slider down here it tells me fewer and fewer parts are available. So let's Go 1.2 Vols and under we've got 31 Parts out of the total of 87 up here.

So it it tells you I I I Like it. It's a pretty good uh sorting capability. It's got all the info you want there right in front of you. Now let's uh, maximum IO Let's go the minimum.

It's got to be greater than and let's say 1 and 1/2 amp Bingo We're down to four parts. There you go. Once you start sorting these parameters down, it comes down pretty quickly. Now the Max: 7 1708, 1763, 1709, 1703 Um, this one down here.

the 703 one cell to three cell high power. Oh 1.5 amps. Here we go. This might be a winner.

Let's check it out. Well, let's hope it is. It's in an So I See1 16 package, so that tells me that it's reasonably higher power than some of the other Um packages we've been looking at. Um, it's It's certainly a little bit bigger.

So let's go down to the max 1703 one cell a look at popup God No I Do not want to. Yeah, you may be selected to take part in customer satisfaction survey. No go away God No thanks. Should the button should be called? Piss off? Not no thanks.

Anyway, let's not muck around. Um, well no I just noticed uh, something down here. It's 140 mli 75 milliohm n Channel mosfet switch 2 amps That's pretty nice. So let's download the data sheet and take a look at the maximum 1703.

And once again, let's notm around. Let's go down to our parametric graph down here and effici Icy versus low current at V out 5 Vols on the left hand side here. now. uh VN 1.2 Vols Now let's look at this one.

Uh, as you can see, it's look. it's getting up there. 100 200, 300, 400 Oh look, it's going to do it. The graph actually stops at about 350 milliamps.

Uh, sorry, 4 50 milliamps. So it's all. That graph almost goes to 500. If you extrapolate that graph, this one here is the one we're talking about.

If you extrapolate that down a little bit further, it's going to plummet at 500 milliamps. Here, it's going to be about still about maybe 65% to 70% efficient at a VIN of 1.2 volts at 500 milliamps I Think we found a winner. It's a shame that it does doesn't have a lower um input voltage graph, but you know 1.1 Vols isn't much lower than 1.2 So you can sort of you know, guesstimate where the graph is going to be and the efficiency? Well, it might be down at 50% at one Vol input. You don't know you'd have to actually measure it, but it looks like after all that searching, we finally found a chip that actually looks like it might do what we want.

It certainly looks like it's capable of getting 500 milliamps out of it or pretty close to it for a good part of the input battery range. And that's what we want Even though. Um, because once you get down to 1 volt, that's you know, the lower sort of 30% of the battery capacity or something like that. but the majority of the battery capacity uh, will occur at greater than 1.2 volts.

And if we use a Lithium uh ablea cell instead of an alkaline alkaline sell, then we'll get even better performance again. So this one looks like it's going to do do the job. So the max 1703 I think we might have a winner here. So let's go over to Digi Key and go Max 1703 And once again, we didn't see that Max 1703 in our parametric searches on Digi key so we had to go.

This is an example of how you have to go direct to the manufacturer's website um often to actually find these parts. You can't just rely on the uh on the supplier like Digi key and their search capability. So let's go down here. Let found it.

Uh, do they have them in stock? Yes, they got them in stock. Quantity available: 852. That's reasonable. but look at the unit price.

12 bucks and 10 and9 for one chip? Jeez. God You can buy a rocket for 12 bucks. Fly to the moon with that. It's crazy.

But the the hund of price down here? Oh $548 at even a 100 of price. And if we go back to Maxum here and they should have a typical that's a Digi key price. if we look at Maxum they'll have a typical price. Here it is down here.

there it is. It's $329 at 1K quantity so you can buy them directly from Maxum They do sell them, sell them themselves direct I believe. so you should be able to get them for $329 Bit more expensive than I wanted, but certainly not out of the ballpark. So I like it.

The Max 1703 I'm going to call that one a tentative winner, but of course that's not the end of it. Let's take a look through the data sheet a bit further and Let's uh, look at some other stuff. Here's an interesting one: Startup Voltage versus Load Current: Now, this is important because if your converter can't start up, then you've got a real problem now. Um, due to the nature of this design I Don't actually expect it to start up at low uh battery voltage as I expect it to start up with a fresh cell and that's it.

It'll just use up all the cell and it shouldn't have a requirement to start up at low voltage. So this is interesting: Start up voltage on the Y-axis versus load current on the X-axis down here. So let's look at 1.5 Smack in the middle there the startup current. It looks like at 1.5 Vols it can do 200 300 milliamps.

So anything greater than 300 milliamps uh, load current. it's not going to be able to start up. So really, that's requ that's dependent upon um, that's that. That might be pushing it for the design.

I'll have to actually try it out practically and see if it works because if the load comes on instant, which it may not with this device. Um, in fact, you can use it in a mode where the Um output isn't loaded until such time as you plug it in so the regulator would start up first and then you can plug it in so it shouldn't be too much of a problem. Let's have a look at some other stuff. this.

uh Peak inductor current limit versus output voltage for Pwm mode. That's uh, quite interesting. an output voltage of 5 Vols it's about 2. uh7 amps uh output current limit.

So this chip, it looks like it actually has Uh current limiting um capability. Uh, basically. so so that um might be a potential trap if we try and use it um in um in in an actual circuit where we're trying to maybe overpower the thing or you know, uh, over over speec the thing so it might actually shut down on us. So we just have to be careful of that and we'll have to actually try this chip out in a Um mockup prototype first just to make sure it can do the job.

Now of course I know what you're thinking. There's more than one uh component manufacturer out there, so let's try. Mouser shall we? DC Converter: Let's type that into Mouser and see what sort of parametric search it has. So semiconductors down here.

We want 3,666 devices. There we go. Power Management Ic's that's what we want. and let's go to DC to DC switching converters 1,544 cuz you want the converters instead of the controllers, just watch out for that there.

Normally those controllers are normally used in Higher Power Systems um that have more more discrete components, external uh, fets and things like that. So we want a switch in allinone switch in converters. So let's go down into there and W look at the parametric surch they got. It's hardly anything.

It's hopeless it it. I Don't think it used to be like this. There something changed in Mousa but all they got is through hole and SMD and case and packaging. You? you going to be kidding me? So let's go to the through hole.

sorry the um SMD devices, but look, it just doesn't work. It's hopeless. What's the point of that parametric search at all? Just none. So we can limit products to manufacturers which is quite good.

Um, but really? I mean god, let's go down to Maximum Products down here and select manufacturer and once again, it still hasn't given us the parametric search we need. So Mouser is absolutely hopeless for DC to DC converters. compared to Digi Key Mous can be great for other stuff I found but in this case it's next to useless. Unless you're searching for a price which we'll search for our Max 703 here we'll type that into Mouser and we'll get um yeah, they've got 215 in stock.

they at $16 for a one off. um $788 for 100. so that's pretty much all it's good for. So there you go: I Did actually search uh, many other manufacturers as well I used their parametric searches directly on their sites and I couldn't find anything.

The best. The closest device I could find is the Maxim Max 1703 device here which looks like it will get fairly close to my requirements. but I have to build it up and find out. But these parametric searches usually uh, you'll usually get like uh, three four five devices turn up that will suit your particular requirements.

you might even have more. It's it's fairly rare to get down to one device which is your only choice. um cuz uh, if you got three four Five devices available, then you choose the one with the lowest price. the best availability, the best footprint, the best features which have you know I might have some stuff built in you might need yada, yada yada but um, the best I could do here is Max 1703 now.

I Also searched for devices with external fets as well and I still couldn't find anything um suitable. So there are two other options left either. apart from use the Max 703 which I am going to try out I'll I'll uh, breadboard that up and see what it's like. The other option is to actually get multiple DC Todc converters like this and actually put them in parallel and then sum them at their Um diode uh, the actual cathode of the diode here.

but that's a bit tricky because then you, how do you equally share, uh, load across across the various regulators? And but it might turn out because this Max 1703 is quite expensive. so it might turn out that um, it might be more cost beneficial to use five of those little cheap microchip devices at you know, 40 cents each or something like that. five of those with uh, but then you're going to need five diodes and you know, five inductors and stuff like that takes up more room. But hey, it might be more cost effective.

so if your design is cost driven, you might look down that. Avenue But um, I'm not so necessarily cost- driven in this respect. um, that I'd have to resort to paralleling DC to DC converters, which is a pretty tricky business. you've um, it's quite hard to share power across these converters.

they can upset each other and one Hogs all the current and that just gets really nasty. and the third option would be to uh, roll my own DC Todc converter. Um, but really, I don't want to go there I haven't got the time nor the enthusiasm to dick around and try and do that sort of stuff. So I think there you go I'll just buy the max 1703 and suck it and see.

So there you go I Hope that was, uh, interesting that this is a typical design example uh, where it was actually quite hard and even though I might have compressed this into I don't know, 20 or 30 minutes however long I've been going. um I've actually spent much, much longer looking through all these data sheets trying to find all this stuff. It's crazy and this is just for one part. For a simple Step Up DC to DC converter, you can see how much Works involved, but this is what a typical design engineer would do.

A lot of the time they're just looking through data sheets parametric searches trying to find suitable parts. So good luck when you're trying to do this. See you next time.