Five things every Engineer should know about PDN

Focus:

If you hear the term “Power Distribution Network,” or PDN you’re likely to think of a power scheme used to power CPUs and FPGAs. But as the author describes in this short article, PDN concepts apply to all circuits even those as simple as a voltage regulator powering glue logic. Failure to observe certain PDN design rules can lead to numerous circuit malfunctions, which may be traced back to power problems such as loss of voltage regulation or PDN noise. The author spells out five concepts or guidelines that should be considered when designing PDNs in any application. Those guidelines include keeping the impedance curve of the PDN flat (the concept of target impedance is explained); the need for impedance matching; the greater potential for PDN problems at lower clock frequencies; why a dynamic current change can produce a noise voltage that is much greater than the current step times the target impedance; and why load devices with slower rise and fall times make it easier to manage PDN noise. Example measurements are provided to illustrate the concepts.

What you’ll learn:

• How to understand the basic rules of PDN design that apply when implementing power circuits in all types of board-level applications, not just those involving CPUs and FPGAs
• How to avoid PDN-induced circuit malfunctions

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Author & Publication:

Steve Sandler, Picotest, Power Electronics Technology, Oct 02 2013

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