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

Autodesk’s Fusion 360 Merges ECAD, MCAD

05/28/2020 | Andy Shaughnessy, Design007 Magazine
Andy Shaughnessy spoke with Autodesk’s Matt Berggren about the company’s Fusion 360 EDA tool and the new capabilities added to the software. Matt explains how Fusion 360 blends ECAD and MCAD functionality in one environment and at an affordable price, and why he believes it will help round out Autodesk's electronic portfolio with end-to-end capabilities.

Ventec Book Excerpt: Thermal Management with Insulated Metal Substrates

05/28/2020 | I-Connect007 Editorial Team
The following is an excerpt from Chapter 1 of "The Printed Circuit Designer's Guide to... Thermal Management with Insulated Metal Substrates," written by Ventec International Group’s Didier Mauve and Ian Mayoh. In this free eBook, the authors provide PCB designers with the essential information required to understand the thermal, electrical, and mechanical characteristics of insulated metal substrate laminates.

This Month in Design007 Magazine: What Did You Expect From Me, Anyway?

05/14/2020 | Todd Westerhoff, Mentor, a Siemens business
As engineers, we work in the middle of a (usually long) process chain. It’s sort of like working on an intellectual assembly line—we get requirements and data as input, perform our particular task, and then provide our output as requirements and data to the next person on down the line. It seems easy enough. So, why is it that so many of the requirements we’re supposed to meet and so much of the data we receive is downright bad?



Copyright © 2020 I-Connect007. All rights reserved.