General > General Technical Chat
Do semiconductor datasheets suck?
magic:
Include complete absolute maximum ratings.
I have seen 21st century chips whose datasheet fails to mention the existence of some clamping diodes :palm:
It's also nice if diodes are specified to survive X mA of clamping current rather than just "VCC+300mV".
magic:
--- Quote from: dmills on November 26, 2023, 12:11:03 pm ---Opamps (and things containing them), it would sometimes be useful to know which supply pin the Vas integrating cap connected to, you can sometimes infer this from differences in PSRR between the rails, but it would be good information for a designer to have directly. If your part utilises 'Bias current compensation' please specify levels of correlated current noise, far too many of them don't, and it is a nasty surprise when the input impedances are unequal and suddenly excess noise appears.
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Actually, why would you want to know the compensation thing if not for the reason of PSRR difference?
Hard to disagree about bias cancellation. Plenty of confusion out there and occasionally outright lies, i.e. noise specified using creatively designed test circuit which makes it look lower than everybody else's specs.
The crown goes to Microchip for their auto-zero opamps with 1pA bias and 100pA offset. What it means is that bias is ±50pA, but opposite polarity on the two pins.
PlainName:
I would like to see a typical application circuit. And a description is what the thing is used for, not just what it does.
16bitanalogue:
--- Quote from: T3sl4co1l on November 27, 2023, 09:02:06 am ---Pet peeve: leakage current missing from inputs. So often I've seen regulators with ~1k resistors when 100k+ would do; why waste power unnecessarily?!
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As a general rule, reading through the ABS MAX will provide a clue for diode clamps. If ABS MAX on an op-amp input pin is VSS + 300mV and VDD - 300mV then that indicates a diode clamp, and I would expect leakage. Many digital I/O pins should have it in the EC table, along with other specific pins (BIAS, an LDO style input on many converters/controllers). If you do not see it listed it is usually not considered important for most customers.
Generally speaking, a product is defined for a customer and their application in mind. There is a back-and-forth with that driving customer over the entire datasheet. First release just considers their needs. Of course as other customers gain interest, they may have other questions, use cases, and limits that the datasheet may not currently include. In most cases, I and my team will update the datasheets with new requests.
For pole/zeros, zener style clamps, what the input structure looks like: you are preaching to the choir. There are instances where information is purposely vague, because we only target specific vertical markets and we want 1) customers to ask those questions, 2) keep info out of the hands of our competitors.
#2 is debatable, there is nothing to stop a competitor from ordering a sample and an evaluation board. So :-//
--- Quote from: T3sl4co1l on November 27, 2023, 09:02:06 am ---Do manufacturers do research and prototyping labs anymore? I mean of the sort like the classics played around with. Like how the LM13700 datasheet has dozens of applications, because, well it has to, it's a somewhat unusual part (it's not your bog standard op-amp), but also those were well-known and practical applications for the function at the time.
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I been around a while. Different companies, different groups within the same company. In one sentence: "Is there a business justification for this?" I have always had to justify why I want to write an application note, create a design sheet, or create interesting circuits. It really depends on the type of product and if there is a justifiable need to tinker in the lab. Most tinkering is with tools (programming, hardware) to help make our lab testing easier, but this is specific to us and not a customer. I blame the MBA's.
--- Quote from: T3sl4co1l on November 27, 2023, 09:02:06 am ---Also the perennial: Why do Application Notes suck SO BAD? :-DD
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Depends on what you mean by sucking so bad. The reality is app notes (many, not all) are conceptual and tied to a release of a product to help promote it. The other reality is the authors will have varying levels of education, experience, and practical knowledge. This is all very generic, but if someone expects an appnote to be some 6-sigma design over PVT (process, voltage, temperature) for the device and passives, you are looking in the wrong place. They are not meant to be "copy this and you will have no problems". This is a long winded way of saying, app notes (modern app notes) are MARKETING material.
At least the designs are simulated to help bolster the concept, then some may actually be built in the lab and tested. TI and ADI have circuit designs to this affect.
16bitanalogue:
--- Quote from: T3sl4co1l on November 27, 2023, 09:28:04 am ---BTW regarding "typ", is there an industry standard for how this is determined? Some kind of mean, I'm sure (most often arithmetic, but maybe others depending on statistics), but nobody and I mean NOBODY ever gives σ, or histograms or anything, unless it's something very particular (e.g. precision op-amp Vos histograms aren't uncommon). Is variance literally prohibited?
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I do not know of an industry standard. There is a team that oversees quality which includes how devices are tested to help with wafer yield. I can only tell you how I have seen it done over my many years, and there is variance (no pun intended, :-DD) from company to company.
1. One company would take worst case skew lots (https://en.wikipedia.org/wiki/Process_corners) and a few hundred parts and test them all over voltage, and temperature to gather statistical data.
2. Another company only looked at a typical lot of a few hundred samples over voltage and temperature to gather statistical data.
Which is better? Above my pay grade. I trust the engineering PhDs.
The production test limit is wider than the 6-sigma limit, and in turn the datasheet MIN/MAX is even wider than the production test limit. Statistically, you should never see a part anywhere near the MIN/MAX limit in the datasheet. You are either measuring wrong or the part is damaged. Rarely, and the most dreaded fear of any company, it is a test escape. Code Red.
Now, you will always here "Design to the MIN/MAX which is worst case." But we all know now that MIN/MAX limits are often well beyond 6-sigma, so what gives? Depending on who the customer is, we may provide characterization data, so the customer can use their own judgement on their design corners from our data. We still tell them we will not guarantee it - and I have seen on a few occasions a process shift. It may still be within final test limits, but that could still be a problem for the customer.
This may not always be true. Say for example, a group may get a waiver to have MIN/MAX only be 4-sigma and accept the yield loss.
I do believe it is beneficial to add sigma limits around the typical in the performance graph, but that is just me.
--- Quote from: T3sl4co1l on November 27, 2023, 09:28:04 am ---Also showing how min/max is calculated ("guaranteed by design" vs. 6σ vs. test limit range) would be nice. Maybe that's something else assumed (industry standard), I don't know.
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Hopefully, my previous answer helps with this as well.
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