Skills for the Coming Market: Reading Datasheets

Electronics engineers will (hopefully) learn plenty during their educational experiences at university, but there are some important skills that they don’t teach. A lot of these are learned on the job, but there are some skills that should be taught in electronics engineering courses. One of these skills may sound basic but it is absolutely important for front-end engineering and schematic capture: how to read a datasheet.

Datasheets contain tons of valuable information, but how can you parse through it quickly, find the most important specs you need for a design, and ultimately land on a useful part? We’ll show you what to watch for in this article.

What’s the Challenge With Reading Datasheets?

Reading a datasheet, decoding the technical vocabulary, and inferring the intent or context of the datasheet author is something a new engineer is expected to just figure out. Part of this problem is that datasheets already contain a wealth of information, including for ICs, and there is no room to “dumb down” the information to a basic level. After a bit of handholding from a senior engineer, and some mistakes along the way, a younger engineer can usually figure it out or decode the technical lingo found in datasheets.

The other reason this continues to be a problem is that this is not covered in any technical courses or engineering courses. Students might be required to read some information from a datasheet in a lab class, but it’s usually checking the main specifications (power, frequency, etc.) and not looking at the finer specifications that are required to build a reliable, functioning product.

What to Watch For in Datasheets

Application Circuits

The application example you see in a datasheet may not be universally applicable to other designs. This one should not need too much explaining, but it’s easy for a new engineer to get carried away with using an application circuit before looking at its specifications and making reasonable modifications.

Make sure you understand how you can change the specs on this type of application circuit.

So before you start replicating an application circuit in a new design, do the following. Compare the circuit with your design’s performance specifications and limits. If you can’t hit your required limits with the part based on the application circuit, you will know by comparing the comprehensive specs and the application circuit specs. If there are no specs, then consider a different part that allows you to more easily re-engineer an application example into a custom design.

Guaranteed vs. Derived Performance

The rating you see in a datasheet will be specified against some test condition or operating environment, and so it can only be guaranteed at that one test condition. If your circuit will differ from the test circuit being specified in the datasheet (it almost certainly will be different), then more information is needed to qualify the part.

Instead, look for graphs that show comprehensive performance across a range of operating conditions. If the performance specs don’t exist for your application, and you need a specific spec for the design, then pick a different part. Some of the best manufacturers will include this test data directly in the datasheet, rather than putting it into an application note or a different technical document. While graphs can’t capture every test condition, they should give enough data for you to interpolate the performance at your operating specs.

Understand the Lingo

Datasheets do their best to use language that matches industry standard terminology describing part functionality, performance expectations, pin functions, pin naming, and a host of other data points. This is one of those areas that can be difficult for new engineers because there are not enough online resources for learning the vocabulary. As a result, most engineers pick this up common terminology through experience.

However, for some component-specific terminology, datasheets may include specific sections that describe a concept or performance specification in greater detail. Make sure you fully understand these sections; they may contain useful notes or equations that are absolutely necessary for your design to function correctly. Don’t just assume that the application circuit is the only piece of information needed to build a custom system.

Datasheet Revisions and Production Status

Just like components have a production or lifecycle statuses, datasheets will also have production statuses and release revisions. The datasheet status should align with the part lifecycle status:

• Active - The specifications are fully tested and qualified.
• Preliminary - This is an initial release and the part specifications or use case information may change.
• Not recommended for new designs (NRND) - The part can still be purchased, but newer options are available.
• Last time to buy (LTB) - The part is near the end of its lifecycle and production of the part will soon end.
• Obsolete - The part is no longer produced, although stock may still be floating around with distributors.

Quality Manufacturers Create Quality Datasheets

The previous point brings up something else that is very important: the quality of a datasheet reflects the quality of the components. If the manufacturer of the component can’t be bothered to include the above information, then you shouldn’t be bothered to use their products. Many of the leading semiconductor companies like TI and ADI/LTC pack tons of data into their datasheets, and all of it is very important for ensuring you can build a fully functioning product with a vendor’s components.

No matter what designs you want to build, the best way to get started is with a powerful industry-standard PCB design tool like OrCAD from Cadence. Only Cadence offers a comprehensive set of circuit, IC, and PCB design tools for any application and any level of complexity.

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