 The Great Search brought to you by Digikey and Adafruit. Every single weekly data user power of engineering, WSU, find the things that you're looking for on digikey.com. Lady, what is the Great Search of the Week this week? Okay, so this week I'm working on this power delivery chip which would negotiate with a USB wall adapter. And like I have one here, for example. And this wall adapter, you know, it's, sorry, this is USB type A. I had a USB type C, oh, it's over there. Hold on one second, I'll get one. Okay. One second, I'm not going anywhere. Breaking the fourth wall. Yeah, but I mean it's, I mean people understand I have legs, I get up once in a while, okay. Yeah, it's not like the Facebook virtual world where the characters didn't have legs. Okay, so this is a USB adapter with USB-C on it. And then let's go to the overhead real fast and I'll just show the text so people can see it. Okay, so this, I'm gonna focus on it. Okay, so you can see here this has multiple outputs possible. So, you know, there's only one plug but it can give you five volts, three amps up to 20 volts, three and a half amps. And when you connect normally, if you don't do anything special it'll give you five volts and be like, hey, you got five volts and this is, be happy with that. But there could be some cases where you have motors or big battery packs or something you wanna negotiate and get higher voltages, maybe up to 20 volts. That's the maximum that you can get from USB Type-C. And to do that, the device on the other, so this is PD, power delivery. The device on the other side has to negotiate. It has to request that higher voltage and it isn't as simple as just setting a couple resistors. It actually has to do this bi-directional communication where it sends data back and forth to say, hey, what voltage can you supply and how much current and how much do I need and it's what I want and it's non-trivial. So to do that, we're gonna use a helper chip. Let's go to the computer. And the helper chip I'm using right now is the FUSB 302. There's actually a couple different chips that do this but this is the one I picked. It's low cost, it communicates over I squared C. It's available on digikey.com for like 60 cents and we'll show that. And what it will do is that this V-bus when you first turn it on, it'll be five volts but then you can communicate over the CC lines and this chip is going to say negotiate up to 20 volts. When it goes up to 20 volts, I still need this regulator here that provides 3.3 volts to work. This needs to work no matter what. I don't need a lot of current, maybe only 10, 20 milliamps but I do wanna be able to have it function and not blow up even if it goes up to 20 volts and I want a little bit of headroom above that too because you can sometimes get 21 volts out of the USB PD and then maybe there's a little bit of spikiness and so let's say 24 volts, right? Just to give ourselves a 20% engineering margin. I need to spec a regulator that can give me this. So let's go to digikey and first off, I'll show you the FUSB 302. That's the chip I'm using. Yeah, so this particular one isn't in stock but yeah, this one isn't stock. So there's a whole bunch in the family type C controllers. They're apparently inexpensive. They're like 50, 60 cents, which is a great deal. So you just like plop it on. It's not even very big connected to the CC lines and over I squared C you have, there's little drivers that are published everywhere from various platforms. Tell it what you want. But like I said, it doesn't have a built-in regulator. As far as I can tell, you need to connect an external three volt regulator that can run off of the V USB no matter what. So let's find a 3.3 volts LDO. And so the question is, why am I using the LDO not a buck converter? Mostly because I'm cheap and I don't need a lot of current. A buck converter would totally do a great job here but it's gonna take up more space. It's gonna cost more because I'm gonna need a diode and I'm gonna need an inductor. I don't need that much current. I'm pretty happy with a very simple LDO that costs maybe 10, 20 cents. It does the job and then I can always redesign this later if I need more current, which would necessitate a buck converter because the power dissipation would be too high, especially if I'm requesting 20 volts or 15 volts. All right, so voltage regulators. And there's a lot. I've already kind of pared it down because I said 3.3 volts but let's just go to the plain regulator. So if I don't specify 3.3 volts, there's 70,000 regulators. There's a lot of stuff in stock. So let's look at active. Let's look at ones that only have a positive output. One regulator and fixed output type. And I also want it to be in stock. So that'll get me down to about 10,000 pieces. Next up, the voltage output I want it to be fixed. If I was willing to go with a adjustable, I set it with a resistor divider. There'll be more options, but frankly, there's a lot of options already. I don't think I need, it turned out I found so many that I was like, you know what, why have two resistors if I don't need them? So many LDOs have 3.3 volts output. All right, so now I have 1,700 options. Next up, I don't care about the dropout so much because again, I did a lot of current. For current output, I did want at least 100 milliamps. You know, I don't think I'm gonna be able to get seven amps but you know, I'll go all the way up there just to be complete. I do want it to be surface mount, not through a hole. I don't want a TO 22 or whatever. And the voltage input. Now remember, the tough part about this, not the tough part but the challenge, is that this V bus, which nominally would have been five volts now can be up to 20 volts. And so I need to make sure that my regulator can handle it so I can't pick anything too low. There is 20 but again, 20 is really cutting it close. You wanna give yourself a little bit of margin. So let's give ourselves up to 24 volts. I don't think 120 is gonna give you anything but for completeness, I'm gonna select everything above 24. Okay, so now I've got 300 options. Let's look at some of what we got here. So lots and lots of options. This is a very common issue. You know, one of the things that you'll have to decide is the trade off between packaging and power dissipation. So in general, the bigger the package, the better your power dissipation. You'll have to calculate, if you have 20 volts, if you have 20 volts of output and you are doing 3.3 volts, that's 16 volts difference. And then let's say you're drawing 20 milliamps. So it's a third of a watt. You know, if you're driving, if you're, you know, because the voltage difference times the amount of current that's how much heat you're dissipating. You know, for this design, I think I'm gonna just warn people, hey, like you're not gonna get, I don't need more than five to 10 milliamps of drive, the chip itself. But if you want to use that for other circuitry, you know, you may not, and you've got the 20 volts output, people have to kind of realize like, hey, you know, I'm not gonna be able to get that much current out of it. I think that's fine as long as I document it. I'm going to still stick with going with a SOT 23.5. Although, you know, I think I might do some more math and verify, I don't need a SOT 89. A SOT 89 is like, it's a little bit bigger, but it has a very good, you see that big tab, it's a nice big heat sinking tab. That said, you know, I think if you see, or you could go with this, a HT SOP 8 with a big power pad on the bottom. So, you know, again, calculate how much current are you gonna need. You need a lot of current, this TO 225 will dissipate like a watt or more. Let's go with the SOT 23 size. So, go over here, and I'm gonna get, I'm gonna skip this SOT 89, let's do the SOT 23. I'm gonna do the five pin version, which I kind of like, because it has an enable pin, and it's also kind of a well-known version, although, well, maybe I'll select these as well. You never know. And then SC 74, that's the smaller version. Well, I'll select also. Okay, so now I've really got not that many options, but you know, if you don't need an enable pin, three pin version will work fine. I tend to like having an enable pin, I don't know why, but this is kind of funky, it's like a caterpillar of some sort, eight pin SOT. Don't see a lot of those. All right, so, a lot of good options. I don't really care about quiescent current, that's something that if you want, you can care about. You know, voltage max again, you know, I don't think I need the higher levels, but let's look at, you know, there's quantity available and pricing, and I kind of like to do a balance between the two. Some really good options here, 36 volt, 24 volts, fairly good dropout, all these have good current capabilities. The RT90 series, GPS 7933, all of them are, you know, good price also about 50 cents or less, but I was actually kind of into this MCP718 BSN, I'll tell you why. Given that there's like a bazillion options, there was, you know, like 30 options available and more if I was willing to go with a different package. This one, you know, if you have five to nine volts, it will give you 300 milliamps out. So at a lower, you know, as long as you're within the power capabilities of this package, you can get 300 milliamps, which is kind of nice. So if you're happy to negotiate, again, maybe you're negotiating only five volts, but you want, you know, five amps, the dropout small enough that this 300 milliamp drive won't, you know, dissipate too much heat. The price was really nice. It was only 25 cents, what a good deal. And then, you know, looking at the data sheets, this used the standard pin out. There was actually one of the chips that I found there didn't have the standard five pin, sought 23.5 pin out. And it was stable with ceramic capacitors, just something to watch for, sometimes or not. It had thermal shutdown and current limit protection. So again, if people tried to overdrive them, drive it at high voltages, it would be fine. And I've always had really good luck with the on semi voltage regulators, also very low quiescent, which is kind of nice. So all together, you know, a pretty nice little regulator. So this is my pick, MCP718, that's what I'm gonna use. That's a great charge.