Choosing and Using Bypass Capacitors (Part 1 of 3)
By Tamara Schmitz and Mike Wong, Intersil Corp.
Courtesy of Planet Analog
(06/19/2007 5:51 PM EDT)
(Editor's Note: Part 2 and Part 3 will examine common capacitor types, tradeoffs, package types, sizing, bandwidth issues, and application examples. Also, see the list of other recent articles by these authors, below their biographies at the end.)
Parts 2 and 3 of this article seem not to have been e-published yet, but sound good.
By Tamara Schmitz and Mike Wong, Intersil Corp.
Courtesy of Planet Analog
(06/19/2007 5:51 PM EDT)
(Editor's Note: Part 2 and Part 3 will examine common capacitor types, tradeoffs, package types, sizing, bandwidth issues, and application examples. Also, see the list of other recent articles by these authors, below their biographies at the end.)
Bypass capacitors are found in every working piece of electronic equipment. Most engineers know that systems, circuits, and individual chips need to be bypassed. The methods for choosing bypass capacitors typically follow decisions of tradition instead of optimizing for any particular circuit. This article aims to bring the design aspect back to this seemingly simple component. After discussing the motivation for using bypass capacitors, we form a vocabulary around the basics: equivalent circuit, dielectrics and types of available capacitors.
The next step is identifying the primary function and environment of the bypass capacitor. Circuits that exhibit large current spikes have different bypassing needs than ones that solely operate at high frequencies. A few special options are discussed, like scaling multiple bypass capacitors, as well as the importance of board layout.
...
We have three questions to answer before grabbing the closest capacitor:
1. What size bypass capacitor do we need?
2. Where do we place the bypass capacitor for maximum effect?
3. What type of bypass capacitor will work best/adequately in our circuit/system?
4. And a hidden fourth question: what type of package do I need to choose for my bypass capacitor? (which will depend on the size needed, the board area available, and type of capacitor chosen)
The next step is identifying the primary function and environment of the bypass capacitor. Circuits that exhibit large current spikes have different bypassing needs than ones that solely operate at high frequencies. A few special options are discussed, like scaling multiple bypass capacitors, as well as the importance of board layout.
...
We have three questions to answer before grabbing the closest capacitor:
1. What size bypass capacitor do we need?
2. Where do we place the bypass capacitor for maximum effect?
3. What type of bypass capacitor will work best/adequately in our circuit/system?
4. And a hidden fourth question: what type of package do I need to choose for my bypass capacitor? (which will depend on the size needed, the board area available, and type of capacitor chosen)