Most component suppliers view application notes as necessary evils. They are mandatory to ensuring a design's success. But they can be "evil" if the information they contain is not prepared with the same rigor applied to the rest of the development process. Unfortunately, application notes are often given short shrift in that they are "cut and pasted" from one product generation to the next.

In so doing, old information is duplicated and new numbers placed on top of it without any appurtenant analytical work or lab testing. Users assume the data in the application notes is correct and only find it is not when their system fails. Tracing the problem to erroneous information within the application notes is tedious and costly.

Because the task is not viewed as important by the component design team, it goes to rookie engineers.

The real danger from poorly prepared application notes stems from today's high-speed designs, which contain subnanosecond rise and fall times. Those times on which most applications notes are based contain the numbers carried over from the old TTL days-5 to 20 nanoseconds. At those speeds, wires can be 10 to 15 inches long without serious signal quality problems. With most current memory ICs having 300-picosecond edges, wires as short as 1 inch can have problems.

What is to be done about poorly prepared app notes? High-speed pc-board and system engineers must educate themselves about the components and ask questions: What is the worst-case Vcc and ground bounce? What is the fastest edge the part will generate? How much plane capacitance is required to support worst-case switching currents?

Moreover, component suppliers must assume responsibility for the components and their application notes. Every major supplier's application notes contain disclaimers relative to the reliability of using that information in a product design. Some of these disclaimers imply that no matter how carefully an engineer applies the rules in the application notes, if the part does not function properly, it is the engineer's problem. Component suppliers need to spend enough time evaluating their components to make sure the information provided in applications notes, if applied properly, will result in a design that works reliably. To do less amounts to malpractice.

Lee Ritchey is the founder and president of Speeding Edge (www.speedingedge.com), a consulting firm specializing in the high-speed pc-board and system design disciplines.