 The great search brought to you by itford and digi key. Thank you digi key This is the weekly segment where lady to use their power of engineering to help you. Yes, you find the things you're looking at and For on digi key comm lady Eda. What are you looking for this week in the great search? You would never guess it But this one has to do with a part that I can't get anymore. I bet the parts shortage I bet it has something to his parts. Oh good. Yes so this week We are you know, what's interesting is half the time You can tell I do a part shortage because I'm like, hey, I'm designing anything and I got a speck apart and the other half is I'm told by the fabrication team at itford. They're like, hey, like we can't get this when the purchasing team says This part would end of line. We can't get any more. We need your help to find an alternative So we can keep production going. So this week The part that I was told is no longer available Because again, not only is it hard to get some parts but parts that are available are going end of line much faster end of life and are you know, no Other not get you know, not uncanceable non-returnable Which means they're kind of nearing the end of their functionality life. And so You know finding a good alternative for The this part the fan five three three three Even though I think there's a last time by I haven't learned my lesson used to be last time by Meant you could actually last time by does not mean that anymore. It means like it's over. Good luck Maybe we'll send to you to some in two years so this It's this week. We're going to let's go to the computer and I'll show the part that I am getting so the part that we're gonna get is the fan five three three B and I love this part to be honest. It was a high current 1.5 amp internal switch fast 1.5 megahertz switching frequency Super small inexpensive sought 23 5 boost converter for LEDs and what's cool about this is that it was a constant current LED driver, which means that you know if you're Dealing with back lights. So oftentimes, you know, you get a tft anything. That's kind of big like this Like anything that's over like three inch tfts. The back lights are often in parallel So let's look at the backlight diagram Okay, so this is the Display and there's the pin out and then we look at the back light. It's like bam You have six or seven LEDs in a row You want to drive the 20 milliamps But you have to the the V forward for the LEDs is 22 volts and this is not uncommon most largest Flays require a boost converter to drive the LED backlight and The V forward of course is dependent on you know, if you have like what LED? You know, you can use a resistor. You don't have to do constant current cuz it's like, ah, it's three It's 3.4. It's it's you know, somewhere around three ish volts But when you have a bunch in a row and there's variations in the backlight design and variations in temperature and you know Whatever how bright you want to run it? That VF is it's it says 21.7, but that's not guaranteed. It can really vary from 20 to 24 So having something that's constant current you said it look I just want 20 milliamps and you you boost it as high as possible To get to that voltage That's what you want a constant current driver for and that's what the fan 5333 be did wonderfully. I loved it. So up to 30 volts Again did you know 1.5 amps because let's say You had you know 24 volts output divided by 3.3 volts input So it's a seven seven and a half times multiply and then let's say you had a 0.5 Sorry 0.05 amp output So you need at least You know 400 milliamps point for amp current switch, but honestly, I would really double it. You really want, you know, at least 750 milliamp Internal switch current so you don't overload it and also, you know, if you need a little bit more like 75 milliamps You can do it. So this was a really great driver, which is why it's so tragic That it's not available. So let's look at what what it used to be Here we go last time by This is it end of line. So let's find an alternative and I will say it's a little challenging to find a perfect alternative, but I'll do the best I can and One thing another thing is the price was really nice. These are about 60 cents a piece Which is like really sweet. So you do need an inductor You need a diode and these also needed a protection diode. They would actually They need a Zeno diode to avoid going over voltage, but you know, those were cheap. Those were 10 cents So not bad. So let's find something similar again from three to five volt input 2024 volt output Switch current of at least a half an amp But you know as much as possible high speed PWMable and Ideally the same size and pinout. Wouldn't that be wouldn't that be nice? So let's find something. It's a DC-DC regulator. It's a step up with an internal switch and one output I'm not going to set the voltage input min max because of course it can always be a wider range But also I'm a little flexible on it voltage output again. I don't need up to 30. I just need around like 20 Current output. I'll just see what's available I do want surface mount and I don't pick the package case because remember there's Sot 235 and there's T-Sot 235 and both will work. So I don't set this and I set this on the next page So All right, here we are. So let's look for only active items because again, we don't want to we don't want to find things We've already found Next up we do want to set the package So I'm going to go down here and I'm going to select Sot 23 thin or T-Sot Which is also the same as SC-74A I'm like pretty sure that was the one. It's not the same as 70 Yes, 70-5 is the smaller version 74A is the same as T-Sot 235 I will say by the because you know, obviously I do these You know earlier because I again already to make sure I can actually find something There is a lot more options if I'm willing to go to the T-Sot 6 So I will say, you know, if there might be some situation where I'm like, oh if I have to update the design There might be better. There'll be more and better options if I'm willing to go to a 6 pin It's not 236, but again, I'm looking for something that could swap into my current designs to just let me stretch out the PCBs I have now So let's look here and this is already only 35 options So I'm also going to look for stuff that's In stock right now. I will say that there's a couple options are not in stock If it's not in stock, a lot of them aren't coming into stock until 2023 And then the voltage output I will say, you know, I didn't want to limit this because Some of them they were like voltage output But they can actually go a little bit higher than 20 or 21 volts Also the current output because some of these are switch current and some of these are non switch I was like, you know what? Let me I'll just look at the data sheet for each and see what's up next step Search by price because I want to kind of get something close. So the first thing I'm going to look at is this like ZX LD With boost converters, you really do have to just look at the The design so the only thing is that this is actually kind of weird It is a backlight driver, but it's actually like a cell It's for a photo cell photovoltaic cell Input to an LED. So it's it's it's a funky useful thing, but it's not what I want It's not it's not the kind of boost converter. I'm looking for next step is the NCP 5 0 7 also pretty good price about the same looking at this Okay, so this this looks promising because this is you can tell it's actually boost converter and it's meant for a string of LEDs It can do up to 20 20 22 volt output, which is a little bit low But I think it might work fine for most of my designs. You'll read it said about 20 22 volt output Let's look at the current It can do 1.0 watts, which is if you divide by 22 volts about 45 milliamps. So, you know, yeah, not too bad The only thing is I looked at this one and I looked at this and you see it's switch ground feedback and this one is feedback ground and so it's It's not the same. It's the same package was not the same pin out. So You know, that doesn't mean I'm gonna say no to it because I could we route some traces I could still use the same pick-and-place program the same stencil, but I'm not loving this one so far. All right. Next step is the cat 4139 this one Looking so switch ground feedback And this one does switch ground feedback shut down VA and so this has the right pin out just good. It has the right package. It's good It's also says can drive lines up to 22 volts But when I looked Yeah, I'd like to have 22 volts, but it was actually willing to do a little bit above I think I remember I saw it was like, oh, you know, you could go to there's an old overvoltage detection at 23 or 24 so depending on the displays, it might actually be okay and then The switch current is 750 milliamps remember you've got like that's the Multiplied current from the input so that would mean Let's see 22 volts divided by 3.3 There's like seven times so 750 divided by seven so Max a hundred milliamp output, but really I'd say 50 milliamps is probably good. That means Two parallel strands which for that 4.3 inch display it only had one strand But the seven is displays we have have two strands in a row. So that's good to know and It has some open LED detection And it has PWM control So the only thing that was a lot is it wanted a little bit of like it had it was this stir Here to protect their feedback pin, but it wasn't clear if you actually needed it The feedback resistance is a little different. So this uses a 0.3 volts feedback and I believe this one uses Oh, no, it also has about 0.3 volts. So that's good the feedback resistor is the same and You can PWM the the input No more than two kilohertz But it is PWM. Well, which is what I would do for our designs I would use that for the that's how you PWM the LED you actually just like turn on and off the boost converter really really fast So will this work? I mean it doesn't go as high. It's not 30 volts is 22 volts that said I think Given the small number of items in stock like after this The price gets really high and like this boost converter is only 350 milliamp switch And then it's like okay. Now the pricing gets quite high one chip that did look like it was a very good option If if the cat 4139 doesn't work Is the MCP? 1664 this goes up to 36 volts and a 1.8 amp switch so it's it's a really good output and I think I Think the yeah switch ground feedback switch ground feedback So this is also pin compatible the only thing is it's twice the price, but It will definitely do the job. It does that voltage or higher. It does that much current or higher So it's it's kind of an upgrade. So I've got two options. I'm probably going to Try this one for some of the smaller displays like again the ones that only have one strand but if I need You know two strand or three strand something that really wants to push a lot of current or High voltage across the display. I can always go to the the MCP party the MCP one six six four So two options But I'm going to probably start with this one the cat We'll go back here the cat 4139 and there's a couple thousand stocks so I can pick these up and then You know see how they how they do in the design and of course, you know, I'll know immediately if It's not lighting up the backlight or if there's any issues So I'll probably pick some up hot air them on to the backlight controller for some of my displays And just like do they light up bright enough if so? We'll be able to use that. I'll just check each display one after the other If it doesn't work with this one, I'll try the MCP as well All right, that's a great search