Power Integrity: It's not just decoupling caps

-February 11, 2016

If you're looking to distinguish yourself in an up-and-coming area of engineering, power integrity (PI) could be for you. The impressive number of DesignCon 2016 sessions (and a PI boot camp) were indicative of PI's growing importance.

Gone are the days when simple decoupling-cap rules-of-thumb were effective. Even lower speed circuitry needs more care than ever before as IC processes reach gigahertz levels. According to Steve Sandler, one of PI's leading researchers and practitioners, the field is about 15 years behind SI (signal integrity). Wow – talk about opportunity.

Power integrity encompasses the entire power system, from VRM to PCB planes to capacitors to the chips themselves. I learned so many things at DesignCon (though mostly, I learned just how much I don't know), such as:

  • Impedance-match the PDN (power distribution network) just as you would a transmission line (except we're talking milliohms, not 50Ω).
  • The PDN impedance should be as flat as possible. When multiple anti-resonant peaks are excited, rogue waves can result, pushing supply voltage way out of spec.
  • Ceramic caps can be TOO good; consider using ESR-controlled parts.
  • IC manufacturers sometimes sabotage you with poor package design, such that it's impossible to decouple adequately.
  • Evaluate regulators based on output inductance. It's one of the key specs leading to a good PDN.

An anti-resonance peak occurs at the cross-point of package inductance and chip capacitance.

Intrigued by the opportunities in PI? Read (start with the links below). Read. Read some more. Simulate. Design. Practise. Go to conferences. Network. Teach.

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