Why are manufactorers allowed to lie (misrepresent) datasheet values? - Page 1
Forum section: electronics / beginners

author: bitman
author_rank: Unknown
timestamp: October 21, 2020, 02:43:55 am
content: I'm just a newbie - electronics is my hobby. Most circuits I create have less than 20 components, only a few have had 50 or so on them. I make a lot of mistakes - but I try to learn from my mistakes. But it doesn't help when datasheets lie - or try to be so generic that when you search for the right component, you get a lot of false hits.Here's a simple example. I have a 9V power input that needs to drive external components plus a simple ESP8266 which runs at about 200-300mA @3.3V. Lately I've begun to use more SMD components and since I had a handful of AMS1117 3.3V around I used the SOT223 version but that quickly turned ugly.The datasheethttp://www.advanced-monolithic.com/pdf/ds1117.pdfsays it can drive up to 1A. That's what comes up even when you search for similar components. The problem is, given the thermal parameters (JA of 90 C/W). So at a 125 degrees max, at best I can hope to handle 1.33W? So even if I drive it from 5V which seems to be minimum given the forward 1->1.5v I can almost get to 0.25A - not the 1A advertised? Even if you add a SMD heat-sink (I can only find one for SOT223) you get less than 1W of cooling? So not even a 0.5A?I've watched Dave talk about this in some of his videos (tricks for young players) and it seems to just be an industry standard. Why? It makes no sense to me that items can be spec'ed this way overselling capabilities etc? While I appreciate that conditions can differ and extreme environments should be covered, it's amazing why something like this will show up as a 1A regulator?Am I calculating things wrong here? Missing something? I know when I get close 0.4A on the output the AMS1117 shuts down and it's extremely hot. When running it from 9V it shuts down just after 100mA.

author: ve7xen
author_rank: Super Contributor
timestamp: October 21, 2020, 02:56:31 am
content: Maybe you're going to cryocool it?I see what you're getting at, but you have to understand that the datasheet is describing each limit in isolation. The device can pass 1A without failure. The device can work between -40-125C. The device has a Tja of 90 C/W. This is actually more descriptive than combining them all into a graph of 'usable current at 25C ambient vs voltage drop' or something like that. It allows you to modify the parameters and determine for yourself where the limits are, how to derate the parameters in your application, how adjusting voltage drop across the device or Tja (heatsinking etc.) affects it and so on. Nothing wrong with *including* such a chart of course, and sometimes you will see things like this, but if it was *all* that was included, that wouldn't be sufficient.I wouldn't call this lying, or even being deceitful, but you do need to understand exactly what the specifications are telling you and where the 'traps for young players' are. The datasheets are mostly engineering specifications, not user guides, though there's more and more material out there these days that is targeted more at 'here's what you need to know to use this device' and less at 'here are the exact parameters of how this device works, the rest of it you're on your own'. Even some of it is starting to come from the device manufacturers. Look for app notes for more details on actually using devices, but stuff like calculating thermal limits is definitely going to be considered general knowledge.

author: Ground_Loop
author_rank: Frequent Contributor
timestamp: October 21, 2020, 03:04:23 am
content: I don't have a good answer for you, but their phone number is right at the bottom of the page. Give them a call and ask for the 1 amp conditions or example.

author: ejeffrey
author_rank: Super Contributor
timestamp: October 21, 2020, 03:47:30 am
content: Quote from: bitman on October 21, 2020, 02:43:55 amThe dropout voltage is listed as 1.1 V typ. 1.3 V max at 0.8 A (higher but not specified at 1A). You could easily use this as a 5V to 3.3 V regulator. At 1 amp, it would be dissipating only 1.7 watt. Thats too much for air cooling but easily achieved with a small heatsink.Edit: yes you are calculating wrong. The power dissipated by the regulator is Iload * (Vin - Vout), not Iload * Vin. The latter is the total power taken from the supply but some of that goes to the load. So in the 5V -> 3.3V case, 1.33 watt would be reached at a load current of 780 milliamp not 250 milliamp.

author: Berni
author_rank: Super Contributor
timestamp: October 21, 2020, 04:12:54 am
content: Alright then lets do some math:The max limit for the minimum required dropout voltage is 1.3V so lets assume we are turning 5V into 3.7V, so at the rated 1A max this is 1.3W of dissipated power.Page 5 of the datasheet has a table of junction to ambient resistance so with 25cm2 of copper area you get 55°C/W of junction to ambient thermal resistance, so we do 1.3W*55 = 71°C above ambient. So lets add a resonable ambient temperature to it so 30+71 = 101°C. Look again at the 1st page of the datasheet and the rated temperature range is -40 to +125°C so this is fine.It's YOU who is not reading the datasheet correctly. Do you have sufficent copper surface area stated in the datasheet for cooling on your board?

author: S. Petrukhin
author_rank: Super Contributor
timestamp: October 21, 2020, 04:46:44 am
content: No matter how small the loss of power and the release of heat may seem, it must be dissipated - given to the atmosphere, heated air, otherwise it will accumulate and heat up. The permissible current and temperature rise do not tell you that this is acceptable without any conditions. The body of the LM itself may give off some heat, but you need to take care to ensure this.

author: srb1954
author_rank: Super Contributor
timestamp: October 21, 2020, 04:49:30 am
content: Quote from: bitman on October 21, 2020, 02:43:55 amReputable manufacturer's generally don't lie on their datasheets - they just stretch the truth to the maximum extent possible.Three rules for reading datasheets:1) Ignore the figures in bold print on the front page of the datasheet. These figures are put there by the marketing department and the claimed performance can only be achieved under the mostfavourable conditions e.g. it is the 5th Tuesday in the 9th month of a leap year, the wind is blowing from the south at at exactly 15knots and the moon is in the correct phase.2) Read the figures in the specifications table very carefully but take any typical figures with a grain of salt. Only the minimum and maximum specifications have any real meaning and you can have areasonable expectation that the part will meet these figures and that a reputable manufacturer will stand by these figures.3) Most of important of all, very carefully read the fine print at the bottom of the specifications table. This fine print is sneaked into the datasheet by the design engineers and tells you the gotchas youreally need to know to get the part working correctly. Very small fine print is used so that the marketing department doesn't notice these items.

author: bitman
author_rank: Unknown
timestamp: October 21, 2020, 01:27:52 pm
content: Quote from: ve7xen on October 21, 2020, 02:56:31 amThis is really what I find deceptive. This datasheet falsely (in my opinion) states the AMS1117 3.3v can be used at 15V input. Heck, even at 9V the max 1.2W (note 2) is so far off that it's useless. All I can say is that I feel "privileged" not to have the job of finding/sourcing the right components for a living. If everything is to be taken out of context the data/content of a datasheet is relatively useless and comes down to your test given your specific parameters that combined may or may not find themselves at the SPEC level.Not being in the industry I definitely took for granted (obviously being wrong) that when characteristics in the datasheet said 15V max/1A that those two went together. You'll most likely have to work a lot harder for me to not say that's a "lie" or at least a misrepresentation of the truth here. Or put in a different way, had Advanced Monolithic Systems created separate datasheets for each of the AMS1117 chip in the series, the 3.3V would look very different.QuoteI'm definitely not trying to argue that the parameters needed to do the calculations shouldn't be present. I get under different loads and conditions things behave/performs differently. But it's deception to me to both proclaim 1A loads AND 15V absolute max, when 5V is pretty much the only accepted voltage at 1Amp (assuming active cooling and a very specific PCB design for heat decipation). While I definitely understand that the two parameters should be taken in isolation this simply makes the data useless and seems to only be there to mislead.QuoteHaving spent 30+ years in the SOFTWARE industry I'm definitely not in the "young" category except when it comes to electronics (when I was very young I couldn't go down my preferred path of electronics because I'm colorblind - making up for lost time now). I've written and read a ton of specifications for software over the time. I don't have to read the "fine print" when it comes to understanding an API call or kernel configuration option, ethernet specification etc. As a matter of fact, we would call it a bug if parameters documented would under some circumstances produce a crash calling an API - even if there was a note saying "do not pass X and Y and the same time" or "this can take values up to 10 except during leap years where it will crash". So it's not exactly the truth when it's only true under some circumstances that aren't laid out??So I am learning, and Dave is not the first (nor is the thread here) where I see people proclaim the normal of "don't trust what you read in the datasheet" and basically it's up to you to create your own datasheet based on your specific situation. While this situation is completely of my own making I got frustrated as I debugged my "issues" just to find the regulator was what kept shorting out at 200mA loads. I didn't provide any additional cooling because I was so far off the max load (I thought) and now I realize that was a bad miscalculation. But not until I posted my frustration here.QuoteI appreciate it's not a "user guide" and I thought I was not using it as such. My mistake was to take the parameters specified as a whole instead of individual and unrelated specs. I really would like to know how someone who does this for a living finds a regulator that would provide the right output from a known input voltage and load? This unit comes up if you search on 3.3V output and 12V input and 1A. Those values aren't true and if every component result you get is like this, how do you guys get any work done? It's not like there aren't 10k+ regulators out there?Anyway - it will take me a bit of time before I get a chance to reply to everyone who's helped so far. Thanks for all the replies and particular for pointing out where my calculations were wrong.

author: Berni
author_rank: Super Contributor
timestamp: October 21, 2020, 02:04:11 pm
content: It's the job of the engineer to determine if a part is suitable for the specific need NOT the datasheet.The datasheet is there just to give you the required information to do the number crunching in order to determine how well the part will peform in your specific application. Pretty much all the datasheets specify each parameter in isolation since if it had to specify all the different combinations of operating parameters the datasheet would be as thick as a phone book. Besides if all the limits suposebly apply then pretty much every transistor datasheet ever made is 'wrong'. For example take a common mosfet like the IRF3205https://www.digikey.com/en/products/detail/infineon-technologies/IRF3205ZSTRLPBF/1928282The datasheet claims a max current of 75A and a max voltage of 55V. If you are to apply 75A at 55V simultaniusly the transistor would be dispating 75*55 = 4125W so with a 62°C/W Junction to Ambient this gives 4125*62 = 266750 °C that is 50 times hotter than the surface of the sun. Obviusly you can't run it at that power for more than a few microseconds, but suprise suprise the datasheet tells you that with a Maximum SOA graph on page 4. It clearly shows it can hold that for <100us. All the data is right there.You can use that regulator perfectly fine at 15V, you can even use it to step down 15V to 3.3V at 1A too if the load only pulses on for short periods of time. So there is nothing wrong with that, you just have to respect the maximum power disipation of the package.As for how does one find the correct regulator out of the many thousands? You calculate the power disipation before even starting to look for one. If you calculate you need to disipate 2W of power then you won't even look at LDOs in these tiny SMD packages because no matter what space age technology is inside it they will not be able to disipate the required power at that junction temperature. Heck, when you see 2W from a SMD part you might actually start looking at your board design to make sure you can even provide enugh copper area to cool a SMD package LDO at all. So before even opening DigiKey the engineer might decide "You kow what.. this is too much heat to disipate in my small product, this needs a switching regulator instead", but if the engineer does the calculaton and gets 20W of disipated power then they might not even think about using a LDO because they know any LDO on the market will need a large heatsink to disipate it (even tho there are many thousands of LDOs that can disipate more than 20W) so the need for a large heatsink might make the normaly cheaper LDO actually more expensive than a DC/DC switchmode solution.Could you explain how should the datasheet show the maximum current for that LDO? Keep in mind that the number is different dependant on your input or output voltage, ambient temperature, PCB footprint, number of PCB copper layers, thickness of PCB copper, load duty cycle, the product enloshure and airflow, other near by heat generating components...etcThis is the reason why electronics engineers always keep a calculator near by. Its impossible to get our job done without one.

author: tggzzz
author_rank: Super Contributor
timestamp: October 21, 2020, 02:47:22 pm
content: If you think hardware datasheets are bad, let me introduce you to the C language specification!An essential engineering skill is working out what the datasheetdoesn'tsay. (See my .sig)For practice:I say I won't give you a jam sandwich before you give me $10you give me $10what must happen after step 2?

author: rstofer
author_rank: Super Contributor
timestamp: October 21, 2020, 03:16:52 pm
content: Quote from: tggzzz on October 21, 2020, 02:47:22 pmNothing! You didn't say you would give a jam sandwich after receiving the $10.Equally as important as the numbers in the datasheet is the collections of graphs. If you know your operating point, everything else falls out from the graphs.In the case of this regulator, I'm certain that there is at least one operating point where it can handle 1A. But I also notice that it doesn't want an input voltage much more than 1.5V above the output. It is unlikely that the 3.3V version will work very well with 9V input. For certain, it won't handle 1A with that much voltage drop.I think the intended application is to create 3.3V from a 5V supply and this makes sense when you think about today's lower logic levels.

author: bdunham7
author_rank: Super Contributor
timestamp: October 21, 2020, 03:31:59 pm
content: Quote from: bitman on October 21, 2020, 01:27:52 pmStart by realizing that there is no free lunch. For a regulator example, if Vin - Vout is 9 volts, there's no point in using an LDO because the power dissipation is the same either way. Power dissipation capability depends on the physical package, heat sink and the particulars of the installation. If you start by realizing that a design that dissipates 9 watts is going to need to be a certain overall size, then you can quickly see the futility of looking at SOT packages. Specifying parts is often not all that easy, especially if you aren't a pro (which I'm not) but for basic, non-cutting-edge design, you can start by identifying the critical characteristics that aren't negotiable--which may be cost and size, not electrical parameters--and going from there. How you whittle down the 10,000 hits you get on your first search can be interesting, but package size and type is often a good way to go.

author: tooki
author_rank: Super Contributor
timestamp: October 21, 2020, 04:12:49 pm
content: Honestly, when it comes to datasheets, I think both sides of the argument here (“the datasheets obfuscate key information” vs. “it’s the engineer’s job to determine the suitability of a part”) are correct.Having spent probably hundreds of hours reading datasheets since February, Icompletelyagree that datasheets tend to be unnecessarily obtuse. As someone who has worked professionally as a technical writer, I find many of them to be appallingly unclear and/or misleading. Yes, it’s the engineer’s job to understand the specs and apply them, but this is not at odds with a clear datasheet. A typical example is when you have closely related parts in a series. Rarely do the manufacturers tell you what the differences are, leaving you to pore over dozens of pages of nearly identical text, trying to spot the differences, which can be as small as an alternative pinout, a different default setting, or most maddeningly, some internal difference that’s not documented AT ALL. All of these I have encountered in the past half year. For one pair of parts, the only difference was some optimization that was not mentioned in either datasheet, explained only by finding a TI engineer’s response to a forum post by someone equally frustrated at trying to find the difference.Is it the manufacturer’s job to engineer your product? No, but... itistheir job to provide you the information needed to do your job, namely to correctly and efficiently identifyand implementthe best part for the job. And at this, most datasheets fail miserably, especially in the “efficiently” department. A parametric search on the website is no substitute for a human-designed part selection guide. What’s super irritating to me is the fact that such a guide was almost certainly used internally to decide what features and specs to put into each product when they were designing them! Similarly, good documentation on how to implement the part is hugely important, but it’s often presented as an afterthought.For what it’s worth, other than a few instances of incomplete removal of the now-unsupported switch mode (resulting in “when using linear mode”, which now is the only mode), the best datasheet I’ve come across so far is the one for the MAX713 NiMH charger IC. It explains the theory of operation, and does go into detail, but also has a guide telling you exactly how to use the documentation to get it up and running. It literally has a numbered list saying what steps to do in what order. Obviously that’s only possible for a task-specific part, but still, every other charger datasheet took a lot more time and effort. Time that I would have rather spent on other things.

author: rstofer
author_rank: Super Contributor
timestamp: October 21, 2020, 04:18:22 pm
content: In the table of specs, there is Current Limit (the internally non-adjustable self-protection limit) and it varies from 900 mA to 1500 mA with 1100 mA as 'Typical'. Great! It will handle the current without limiting (Typically). However, you are far better off picking the minimum number and perhaps even a bit less - maybe 800 mA. You certainly wouldn't design for the atypical 1500 mA.However, look at the (Vout - Vin) = 1.5V -- that's the important part of that Current Limit spec. The regulator will pass 1.1A ('Typical') or at least 900 mA without a problem in the world if that 1.5V number isn't violated. But that number also gives you a hint: The intended application for this regulator is dropping a 5V rail to a 3.3V rail. They don't intend for this device to have much more than 1.5V drop.But the fact is, you might not be able to push 900 mA through the regulator even if Vout-Vin <= 1.5V. You still have to work through the heat dissipation.Funny fact: The dropout voltage for the OP's regulator is a max of 1.3V while the decades old 7805 has a dropout voltage of just 2V. Yes, the new magic is better than the old magic but maybe not all that much. See Note 4 - the dropout voltage will increase if the current is higher than 0.8A but it doesn't give a spec. The hint given: Don't use the device above 0.8A as the dropout voltage isn't specified and presumably not tested.Thermal may be a lot easier to handle with the 7805 in a TO-220 package and a decent heatsink. The datasheet for the OP's device does discuss the copper area under the SMD package as a heatsink and in great detail. Of course, it provides the area in "least usable units" and I have to use Google to come up with square inches. See Table 1Every single number in the datasheet places a limitation on how the device can be used. It may seem that some numbers are unimportant - right up until you violate one of them. I really like the Safe Operating Area graphs when they are provided.

author: coppice
author_rank: Super Contributor
timestamp: October 21, 2020, 04:22:41 pm
content: Quote from: bitman on October 21, 2020, 02:43:55 amYou haven't described any actual problem with the datasheet. The device can supply 1A. The device has certain thermal limitations. Those limitations mean it can't supply 1A continuously, especially if the drop across the device is large. The percentage of the time it can supply 1A will depend on the cooling you provide. Working out how this plays out as to whether the device is suitable for you is what engineering is all about. Many applications require a generally low current with some short high current bursts. This device looks like a good and well specified choice for those applications.

author: rstofer
author_rank: Super Contributor
timestamp: October 21, 2020, 04:28:48 pm
content: Quote from: tooki on October 21, 2020, 04:12:49 pmAnd some datasheets are better than others. I tend to like National and TI because they typically present more information and better charts and graphs. There will almost always be application information and usually right on point. The smaller manufacturers aren't spending much money on documentation.Of course, if you are a big manufacturer of products, you can just call up the relevant application engineer and they will help you design their part into your product. That's what they get paid for! Alas, hobbyists don't have much leverage. We're lucky if the company has a forum or that one of their people participates on a more public forum.

author: ucanel
author_rank: Regular Contributor
timestamp: October 21, 2020, 04:44:00 pm
content: Reading a datasheet is a language for an engineer to know.For hobbyist engineering is not a hobby sothere is no need to design a document like a tutorial.Datasheet does not need to speak your languageyou need to learn datasheet's jargon.

author: Kleinstein
author_rank: Super Contributor
timestamp: October 21, 2020, 04:56:57 pm
content: There is nothing wrong with the 1117 specs. For a higher current it just needs cooling and of cause the heat dissipation is only from the voltage drop.The bold printed claim are sometimes a little exaggerated or deceptive - e.g. mixing typical and guarantied values and assuming unrealistic good cooling. Cherry-picking also sometime happens: show those data that are good.There are sometimes also actually wrong claims - not all intentionally, but still annoying. Known examples are drift claims in some old days references from Analog Devices and the noise of the ICL7650. A common problem is the SOA of MOSFETs, that with some manufacturers ignores thermal instability and thus the main point of the SOA.P.S.Another odd example is the input bias current specs for AZ OPs. Microchip uses the average of the two inputs, and as these are usually nearly opposite sign the number looks very good - but it is deceptive. Other use the larger absolute value and thus a more relevant larger number.

author: mikerj
author_rank: Super Contributor
timestamp: October 21, 2020, 05:13:58 pm
content: Quote from: bitman on October 21, 2020, 01:27:52 pmWith all due respect this is not a problem with the datasheet in this case, it's a lack of experience giving unrealistic expectations. Datasheets have to assume some basic level of knowledge on behalf of the reader, such as the fact that linear regulators dissipate power depending on current and voltage drop, and that all packages have dissipation limits.The headlines paint a rosy picture of a part by giving the maximums of several parameters of interest, but you should never assume that all those maximums can be applied at once. All the information needed to determine if the AMS1117 is suitable for a given application is in the datasheet, it's up to the reader to ensure they use the device within the electrical and thermal limits given.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 21, 2020, 06:11:47 pm
content: If you brought up the case to a judge, I think you would find a conclusion like: "No _reasonable_ customer would expect that this specification was 'AND', not 'OR'. Dismissed."For example, do you expect your automobile to be capable of its, whatever, 500 ft.lbs of torque, at any speed, in any gear? Or that it's capable of whatever peak output power is, under the same range of conditions? Of course not -- certainly it can't produce that power from a complete standstill, but it's also common knowledge among automotive enthusiasts that there's a torque band, a range of RPM where the engine produces the most torque. There isn't really any other meaningful way to slice that curve, short of plotting or tabulating it -- which would be ridiculous for marketing purposes. The peak is both a simple measure of performance as well as a marketing-friendly number (the highest).This is perhaps a trivial example, but trivial cases have been called before, and will be called again -- I recall there was one a few years ago that hit the news for its silliness, that plumbing pipes aren't the dimensions they say they are. Or maybe it was about framing lumber being similarly off size, or maybe it was both, I don't remember. In any case, a reasonable customer should expect that these are types, not actual measurements. It's dumb, but that's how standards are sometimes.Regarding the electrical matter, the real case is more complicated, because it must. We start with the 'AND' condition (maximum V and I), to outline the operating region in question. Then, it is further refined with dependent conditions.After all, it would be a terrible burden to have to define the complete operating region, under all possible combinations of input, output and environment (temperature, mfg. variation, etc.). Not just to test, but it would be a big burden on the reader to understand such data.Power for example, depends on ambient temperature, device ratings, and thermal resistance. Power defines a hyperbola (curve of constant V*I), which pulls in from the far corner of the V/I rectangle. The voltage in question is voltagedrop, but voltage also has an absolute limit, so we should be mindful of that as well.Note that we can easily push into illegal corners of the operating region: say we use an elevated GND or REF pin to set a higher Vout. This is fine for normal operating conditions (and even standard procedure for some types, LM317 for example), and we can deliver higher than V(abs max) in this way -- the device never sees more than, whatever, across it, thanks to the elevated GND or REF trick. But say the output gets shorted: now Vin-Vout is higher than rating, and it blows up.Tim

author: bdunham7
author_rank: Super Contributor
timestamp: October 21, 2020, 06:15:48 pm
content: Quote from: T3sl4co1l on October 21, 2020, 06:11:47 pmBetter example--buy an airplane with a 'useful load' of 1400lb and a maximum range of 800 miles. Then see if you can take 5 people on an 800 mile trip.

author: rhodges
author_rank: Frequent Contributor
timestamp: October 22, 2020, 12:21:25 am
content: I completely get your example, and it reminds me of my PPSEL written exam. But after owning a C150 and a C175, I wonder which airplane you are referencing? Surely it is larger than a 210.

author: tkamiya
author_rank: Super Contributor
timestamp: October 22, 2020, 12:35:09 am
content: A knowledgeable designer NEVER push those regulators to the limit on spec sheet. However, spec sheet is not lying. With short enough duty cycle you can draw that much. Or, use some exotic cooling method. You can actually draw that much and not destroy the regulator. Of course cost of doing so will be high - but it is possible.

author: tooki
author_rank: Super Contributor
timestamp: October 22, 2020, 12:40:04 am
content: Quote from: ucanel on October 21, 2020, 04:44:00 pmTo me, that’s an elitist and ultimately wasteful approach. There absolutely is a need to design somewhat tutorial-like guides, because even an experienced engineer might never have dealt with that specific type of circuit before.And as I said already, a huge part of the problem is how they hide critical information in footnotes or as a passing comment in the text. Engineer’s’ time isexpensive. I am sure that the annual cumulative cost of the time wasted by engineers having to go through documents with a microscope is in the tens of millions of dollars, if not more. As someone who has written technical documentation for a living before, I am fully qualified to say that there’s a better way. And it doesn’t mean turning the documentation into Fisher Price toys.

author: Berni
author_rank: Super Contributor
timestamp: October 22, 2020, 04:13:55 am
content: Yeah writing a well made datasheet is another thing.Sometimes the datasheet is a unreadable mess with information scattered all over the place. Or the section with graphs contains like 30 different obscure graphs that don't look very useful but are missing some of the most useful graphs that are in almost all other datasheets for similar parts (Like no SOA in a transistor datasheet). I had to reconsider using a part just because the datasheet was missing some key part of information, so rather than taking a gamble on it, i would go look for an alternative part that does have that piece of info in the datasheet just to be sure it will indeed work for my application.Tho these days new guys tend to just follow chip datasheets like a cookbook. That's what a lot of these modern chips are. The datasheet doesn't tell you how exactly it works, it just shows you a rough approximate block diagram of what is inside (where everything is connected to some magical 'controller' box in the middle). It just gives you a schematic of how to connect it and some math on how to calculate the values of external components. And most of the time that works out fine, you just do exactly what the datasheet says and it works first try. However... when you build the circuit and it doesn't work and does weird stuff then these chips are a huge pain in the ass. You can't methodically troubleshoot it because you have no idea how it works, you can just do trial and error of swapping component values until it somehow starts working correctly.

author: SilverSolder
author_rank: Super Contributor
timestamp: October 22, 2020, 04:47:55 am
content: Quote from: tooki on October 22, 2020, 12:40:04 amIsn't that what an Application Note does, though? - I love it when a part has both a good datasheet and a good application note.Sometimes there is a little overlap, I guess. But isn't there a case to be made for keeping datasheets concise, and using application notes for the tutorials?

author: Berni
author_rank: Super Contributor
timestamp: October 22, 2020, 05:01:49 am
content: Quote from: SilverSolder on October 22, 2020, 04:47:55 amYes THIS.Unfortunately its pretty rare to see a really nice well done appnote to go along with it. Even less the sort of app notes that you would see from say Jim Williams where chips get abused to do all sorts of weird and wonderful things with the help of some discrete silicon magic.

author: srb1954
author_rank: Super Contributor
timestamp: October 22, 2020, 05:23:13 am
content: Quote from: Berni on October 22, 2020, 05:01:49 amYes, the quality of app notes has declined steadily since the 1970's when the analog chip designers themselves usually wrote detailed explanations of the internal workings of their latest product showing it off like a proud parent with a new baby. There was an enthusiasm to demonstrate all the useful and wonderful things that you could do with their latest offspring.Nowadays, with just about everything done with digital circuitry, what passes for an app note is usually just a user guide which contains hundreds of pages of terse register descriptions plus a few short example programs (usually poorly commented) that do nothing more than initialise the chip but usually don't give much insight into the sort of things that the chip can accomplish.

author: tooki
author_rank: Super Contributor
timestamp: October 22, 2020, 05:33:23 am
content: Quote from: SilverSolder on October 22, 2020, 04:47:55 amThat’s certainly a viable argument. In the end, the datasheet needs to contain the information needed to quickly and accurately make a good decision on a part’s suitability.But as Berni says above, they rarely make separate application notes. And often, they’re just a note about how to implement a particular thing with it, not necessarily a guide to all the common configurations.Similarly, as I said earlier, selection guides are few and far between.An example of a simple, but good, selection guide isRohm’s catalog. Below is a screenshot of the section for analog sound processors with 3-band equalizers. This table alone let us easily see what differentiates the members of an entire family of closely related parts. TI, for example, utterly fails at providing overviews like this, and the parametric search doesn’t cover all the differences, leaving you to spend countless hours poring over datasheets to essentially compile a table like this on your own.Another good example is Panasonic, which publishes handy charts to help in selecting electrolytics. Attached are screenshots of the charts from theirTHT electrolytics catalogandSMD electrolytics. Everyone should be publishing things like this.Edit: fixed URLs that the software “helpfully” rewrote for me...

author: tooki
author_rank: Super Contributor
timestamp: October 22, 2020, 05:34:02 am
content: Quote from: srb1954 on October 22, 2020, 05:23:13 amSo, so true.

author: magic
author_rank: Super Contributor
timestamp: October 22, 2020, 06:50:16 am
content: Quote from: Kleinstein on October 21, 2020, 04:56:57 pmI was wondering what's the problem with those very high input offset currents on their AZ opamps. Now I know, thanks for the info.I will add another one: LT1028/1128 noise current specification.QuoteIf you run this procedure on any other opamp, even Linear's own, you will get a figure 1.4x less than the opamp's published specification.Their specified noise (1pA/rtHz) is even less than shot noise of the typical uncompensated bias current shown on the schematic (4.5µ → 1.2pA/rtHz). Miracle

author: tggzzz
author_rank: Super Contributor
timestamp: October 22, 2020, 10:44:24 am
content: Quote from: rstofer on October 21, 2020, 03:16:52 pmActually the OP would emit nasal dæmons. (Oops, that's C spec, not hardware spec).

author: newbrain
author_rank: Super Contributor
timestamp: October 22, 2020, 11:44:57 am
content: Quote from: tggzzz on October 22, 2020, 10:44:24 amI disagree. Your example falls in the unspecified behaviour category, not the undefined one.It is not specified whether I'll get my sandwich or not.Unspecified behaviour differs from implementation defined in the fact the vendor is not bound to document it, but it is more benign than undefined.Note: Tongue firmly planted in cheek, (trying to dislodge some crumbles from the sandwich).

author: rstofer
author_rank: Super Contributor
timestamp: October 22, 2020, 03:37:13 pm
content: Quote from: srb1954 on October 22, 2020, 05:23:13 amI'm thinking about the 3 Bobs: Bob Widlar, Bob Pease and Bob Dobkins - giants in analog design. There are many others but these 3 are at the top of my list.

author: rstofer
author_rank: Super Contributor
timestamp: October 22, 2020, 03:43:58 pm
content: In at least one of Dave's videos, he points out that the marketing data on the first page in the upper left corner of most datasheets is to be taken with a grain of salt.A rather humorous approach to reading datasheets:https://youtu.be/KCAqVKeArXsRight out of the gate, the author describes the 'paper' used for most datasheets as being like a tablet but a lot thinner... Just in case his more modern students hadn't run across it.I will have to watch this after I finish the comics.

author: Kasper
author_rank: Frequent Contributor
timestamp: October 22, 2020, 03:58:41 pm
content: I get the frustration. I went through it as a 'young player' myself when I was handed a product that was getting too hot and we (the one HW designer and myself) blamed the datasheet. The limitation of the front page based parametric search is annoying but I can't think of a better way. Can you?The max voltage and the max current are important and once you get familiar with this, you'll know they don't go together.What rating should they put in the parametric search?If they put max voltage = 12V then what should they say is the max current? If they say max rating is 12V and 100mA then someone who wants 5V and 200mA won't even see it in their parametric search and that would make it even harder to find components.

author: ogden
author_rank: Super Contributor
timestamp: October 22, 2020, 04:23:38 pm
content: Quote from: SilverSolder on October 22, 2020, 04:47:55 amYou can go even further and learn from reference designs as well. Not only learn but copy/paste them - circuit, BOM and board layout. I see this very often with SMPS designs and not only. Usually time to market and/or saving on engineering resources is much more important than technical excellence or few cents saved. So you just copy existing, tested and proven design to have more time for part of the circuit which is unique.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: October 22, 2020, 04:39:32 pm
content: Data sheets and app notes really aren't too bad overall. And when you think about it, surprisingly good. The manufacturers of complex ICs don't make their money off of thousands of engineers incorporating their parts into small volume products. And especially not from tens of thousands of hobby folk making one off creations. Their money is made off of very high volume products, and only a few engineers are involved. They are very willing to spend a lot of time with those engineers ironing out the details of their parts interaction with that high volume application. The residual sales to all the rest of the applications don't merit the effort and they don't get it.Making data sheets that work for occasional users of a part is kind of like chumming in the fishing world. I some instances it pays off. But very often it is just pouring money in the ocean.

author: Kleinstein
author_rank: Super Contributor
timestamp: October 22, 2020, 05:12:53 pm
content: Quote from: Kasper on October 22, 2020, 03:58:41 pmParametric search is a different topic, especially if done by third party (e.g. digikey, mouser). It may work well with some parameters, but it can fail with other that are more inconsistent across data-sheets. For some part one may get max values for others one gets typical and than under different conditions. So not every search works - e.g. looking for a MOSFET with high threshold failed, as they mixed typical and max values for different currents, rarely min values.Many data-sheet are really good and the appl. notes are great for learning once you start to understand them. With complicated parts like SMPS controllers the application example is an important part of the datasheet: the relevant parameters may not have a unique name and one need the circuit as explanation what the numbers mean / how they are measured. The example circuit also give you a quick hint of the part is suitable and can do the job you need.However in App notes there are sometimes also funny circuit of the class can be done, but still not a good idea (e.g. there are better, cheaper solutions). To a large part those 3 pin voltage regulator and transistor to boost power circuits belong to this group.

author: Siwastaja
author_rank: Super Contributor
timestamp: October 22, 2020, 05:32:21 pm
content: I don't see any problem listing limits like maximum current, maximum voltage, maximum power dissipation and maximum junction temperature. Obviously, ifanysingle limit is exceeded, there is a problem. It's a ridiculous assumption you could run any thing atalllimits simultaneously, yet you are assuming exactly this.It's like expecting you can run a car at top speed while towing a trailer of maximum specified weight.Withanylinear reg, the more you drop voltage over it, the higher the power dissipation per current, so you'll get maximum current only at low drop-out over the regulator.Your frustration seems to be the lack of understanding the basics of electronic design, not datasheets "lying". This is understandable because there are not too many textbooks about practical electronic design, this is a trade learnt through trial and error in significant part.Of course, additionally, sometimes datasheetsdooutright lie, or mispresent the truth, often on purpose, but the example you have given is not such a case.You may want to look at pre-designed modules; these have simpler-to-understand specifications because the underlying engineering has been done by someone else (and you'll pay for it).

author: jmelson
author_rank: Super Contributor
timestamp: October 23, 2020, 03:07:40 am
content: Quote from: bitman on October 21, 2020, 02:43:55 amThe component (1117 regulator) has a big heat sink tab on it. If you need more power dissipation, attach big copper pours on the board to radiate/conduct the heat. If needed, go to thicker copper layers on the board, or even an aluminum-core board. The maker makes the chip, YOU need to deal with the thermal envoronment. There are data sheets about power transistors with 100+ W possible power dissipation, but you'd BETTER put them on a big metal heat sink!Jon

author: rstofer
author_rank: Super Contributor
timestamp: October 23, 2020, 03:41:34 pm
content: The datasheet covers copper heatsinking in some detail. Single sided, double sided, thickness and so on. "Thermal Considerations" on page 5/8 in the PDF. There is a table of suggested areas and it is large. 2500 sq mm is nearly 4 sq inches. There are smaller areas in the table, some as low as 1.5 sq inches. There is also a comment that there need not always be copper directly below the device nor must the tab be in electrical connection with the copper.It's an area where some experimenting with proper equipment might lead to a decent design. Otherwise, use lots of copper on both sides with a bazillion thermal vias.