Datasheets (Don’t) Lie

Circuitguy shares some tips for reading datasheets. There’s a lot of good advice in here, and it’s well worth checking out. He writes:

“Datasheets Lie.”  I’m sure we’ve all said it before.  I’ve said it myself, and I still catch myself saying it.  Just because we say it, it doesn’t mean it’s true.  Most datasheets are, in fact, very accurate and representative of the part.  Sometimes you have to read all the lines to find the truth between the facts.

[via Dangerous Prototypes]

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  1. > “Datasheets Lie.”

    Yeah, datasheets are marketing documents almost as much as they are engineering documents.

  2. In the defense of datasheets: they are generally created by a single person and that person isn’t thinking about how you plan to use the component/device. Most datasheets are well documented. Meaning, if you expect a certain level of performance from a device you need to carefully understand how the datasheet’s results were produced. The information is there, you need to extract it.

    The idea "the datasheet lies" or "they are marketing documents" typically demonstrates someone who got bit, because they did not read the fine print.

    So that being the case, you need to consider how the person who wrote the datasheet was thinking so that you can apply the device correctly in your application.

    In fact, very few datasheets lie. In most cases when they appear to “lie”, the reader just doesn’t understand what it says.

  3. Jame Lewis is uncommonly wise. If you are of the opinion that datasheets lie, re-read Jame’s comment again. Seriously.

    As someone who has been involved in setting the limits on our company’s IC datasheet, you can talk (and we have) for hours about the details of a datasheet, and which values should be included, but they’re always accurate, in my experience. It’s just in the details and nuance that people misunderstand, because everyone’s application is different.

    For example, take power consumption values for an average microcontroller. If you’re publishing the datasheet, if you set the maximum value that the device can ever achieve, it often involves ridiculously abstract testcases that don’t represent any useful work, and so are not representative of the customer’s actual maximum. Then you’ll get customers complaining the values are too high for their application, because they’re comparing to a competitor’s datasheet where they take a more realistic scenario and get values 30% below your figures, even if the devices are comparable in practice.

    But which value is less misleading to put in a datasheet for a maximum power consumption? A value that will never ever be reached in a real-world scenario, or a maximum value that is valid for > 95% of cases? In the end, you can only pick a policy, then make sure that your assumptions are spelled out in the sheet.

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