Tips for reading datasheets


#1

Component datasheets contain a wealth of information that can lend itself to misinterpretation. Following are some concepts that have been found to apply quite generally, and which are recurring themes in responses to technical inquiries.

Conditions and qualifications apply

  • They apply whether or not they’re explicitly stated
  • They’re as important as whatever they’re qualifying. Perhaps more so.
  • They’re often found in footnotes or small print.
  • Cultivate a habit of seeking this kind of supporting information: if your mother tells you she loves you and you ask what test conditions and qualifications apply, you’re on the right track…

The datasheet describes device behavior under the indicated test conditions.

  • The indicated conditions might closely represent conditions likely to be encountered in practice.
  • They might also represent something completely impractical and unrealistic.
  • Or something in between…
  • Regardless, conditions in your application will likely be different.
  • Device behavior/performance in your application may also be different as a result.
  • Figures given in a datasheet require interpretation accordingly.
  • Good datasheets also provide information on how part behavior changes in response to common variables, such as temperature. Look for the word “coefficient” in the tabular characteristics, and to the graphs often located between the tables and the application section.

There’s a difference between specification and characterization

  • Specifications are guaranteed (subject to conditions and qualifications)
  • Characterizations aren’t guaranteed, they simply describe what’s common, with the understanding that some examples of a part will be uncommon.
  • Both are next to meaningless if applicable conditions and qualifications aren’t known.
  • The portion of a datasheet that’s regarded as a specification is usually quite small
  • It’s usually limited to minimum/maximum values in the parametric tables.
  • The ‘Absolute Maximum Values’ section doesn’t count.
  • If it’s described as ‘typical’ it’s a characterization. Don’t bank on it.
  • The first page, the applications section, graphs, and most anything written in prose generally aren’t considered specifications either.

The datasheet means what it means.

  • This may differ from what you understand it to mean.
  • It might even differ from what most reasonable people would understand it to mean.
  • The parts described aren’t going to change their character to adapt themselves to your understanding, and the datasheet probably won’t be changed to suit your preferences either.
  • If you don’t really understand some portion of a datasheet, it’s a good idea to stop and figure it out. It’s probably important.

Calculating A/H rating on lead acid batteries
Learning electronics