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.



Suggested Items

Why We Simulate

04/29/2021 | Bill Hargin, Z-zero
When Bill Hargin was cutting his teeth in high-speed PCB design some 25 years ago, speeds were slow, layer counts were low, dielectric constants and loss tangents were high, design margins were wide, copper roughness didn’t matter, and glass-weave styles didn’t matter. Dielectrics were called “FR-4” and their properties didn’t matter much. A fast PCI bus operated at just 66 MHz. Times have certainly changed.

Alternatives to Simulation

04/23/2021 | Dan Beeker, NXP Semiconductors
We are living in an age where the demands on electronic product designs are constantly evolving. The IC technology and operating speeds continue to pose significant challenges for teams as they work to develop their products. The increased transistor switching speeds and less forgiving compliance standards make signal integrity and electro-magnetic compliance more difficult to achieve. The status quo seems to have become, “We expect to fail EMC testing.”

Bridging the Simulation Tool Divide

04/12/2021 | I-Connect007 Editorial Team
Todd Westerhoff of Siemens EDA recently spoke with the I-Connect007 Editorial Team about the divide between users of high-powered enterprise simulation tools and those who need a more practical tool for everyday use, and how Siemens is working to bridge the gap. Todd also shared his views on why so many engineers do not use simulation, as well as advice for engineers just getting started with simulation tools.

Copyright © 2021 I-Connect007. All rights reserved.