Quiet Power: Dynamic Models for Passive Components


Reading time ( words)

A year ago, my Quiet Power column described the possible large loss of capacitance in multilayer ceramic capacitors (MLCC) when DC bias voltage is applied. However, DC bias effect is not the only way we can lose capacitance. Temperature, aging, and the magnitude of the AC voltage across the ceramic capacitor also can change its capacitance.

Finally, the initial tolerance needs to be considered as well. In the worst case, we may lose up to 90% of the capacitance for an X5R capacitor, and even for an X7R capacitor. This column will show you the details and also how the most advanced manufacturers are helping the users with new simulation models to take these effects into account.

As an actual example, let us look at one of the capacitors that was extensively tested, where 1uF 0603-size 16V capacitors were tested from various vendors. We further assume that we want to use the part on a 12V supply rail, where the AC noise is low (this will be important later when we take the AC bias dependence into account). Some of the samples were chosen with X5R, some with X7R temperature characteristics. As showed with actual test data , X7R capacitors are sometimes worse for DC bias sensitivity than X5R parts.

If we take the part from Vendor B (labeled B7) in Figure 1, we see that at 12V DC bias we can lose 60% or 70% of the capacitance, dependent on which way the DC bias changes. But when we need to consider the worst-case capacitance loss, we have to consider the cumulative effect of all of the following factors:

  • Initial tolerance
  • Temperature effect
  • DC bias effect
  • AC bias effect
  • Aging

The sample had +-10% initial tolerance. The X7R temperature characteristics comes with an additional +-15% tolerance window for the temperature variation.

To read this entire article, which appeared in the March issue of The PCB Design Magazine, click here.

Share

Print


Suggested Items

Words of Advice: What Concerns You About the Future?

02/14/2029 | Andy Shaughnessy, Design007 Magazine
In a recent survey, we asked the following question: What concerns do you have about the future? Here are just a few of the answers, edited slightly for clarity.

Effects of PCB Fiber Weave on High-Speed Signal Integrity

12/31/2018 | Chang Fei Yee, Keysight Technologies
This article studies the effect of PCB fiber weave on signal integrity in terms of mode conversion and differential channel loss due to intra-pair skew. The study used Keysight ADS 2DEM simulation to observe s-parameter (i.e., insertion loss and differential to common-mode conversion) and an eye diagram for signal transmission at 1 Gbps and 10 Gbps.

Calculation of Frequency-Dependent Effective Roughness Dielectric Parameters for Copper Foil Using Equivalent Capacitance Models

01/02/2019 | Marina Y. Koledintseva, Metamagnetics Inc.*, and Tracey Vincent, CST of America
Knowledge of the correct parameters of laminate PCB dielectrics refined from any copper foil roughness impact and the proper foil roughness characterization are important constituents of modeling high-speed digital electronics designs.



Copyright © 2019 I-Connect007. All rights reserved.