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




Suggested Items

EMA Helps Ease Designers’ Supply Chain Woes

10/20/2022 | Andy Shaughnessy, Design007 Magazine
Supply chain issues are continuing to cause disruptions in our industry, though lead times have dropped from astronomical to merely troublesome. In this interview, Chris Banton, EMA Design Automation’s director of marketing, explains how Cadence’s software has evolved as designers’ needs have changed in the past few turbulent years, including providing designers with component availability data early in the process.

Cadence Provides ‘Clarity’ in Design Tool

08/11/2022 | Nolan Johnson, I-Connect007
Nolan Johnson recently spoke with Brad Griffin, product marketing director for Cadence Design Systems, about Cadence’s Matrix solver technology. They discuss its use as a multi-disciplinary field solver as well as Cadence’s focus on thermal analysis and utilizing the power of the cloud.

HyperLynx: There’s an App for That

08/05/2022 | I-Connect007 Editorial Team
I recently spoke with Todd Westerhoff, product marketing manager for signal integrity software tools at Siemens. We discussed a new capability called HyperLynx Apps that offers a new take on traditional signal and power integrity analysis, and how that fits in with the Siemens plan to put SI and PI tools into the hands of more designers early in the design cycle.



Copyright © 2022 I-Connect007 | IPC Publishing Group Inc. All rights reserved.