**LEARN ABOUT WORST CASE CIRCUIT ANALYSIS**

**UPDATED!**
**Why Perform a WCCA?**

This short white paper explores the Who, What, Where, When and Why of WCCA.

**NEW!**
**Optimizing Electronics Test/Analysis Ratio**

Aerospace MRQW Reliability Conference Feb. 2020 - Reliability is a function of the amount of test and analysis applied.
But programs are often budget and time constrained. So, what is the right ratio? For many programs, no analysis is performed at all as stress & derating and/or worst case circuit analysis are deemed “too expensive or too challenging.”
The usage of COTS components in high reliability applications to save money requires more analysis, not less. And the less we know about the parts and “reference designs” we use the more analysis we need.
This paper discusses how we can use analysis to better complement our testing, Beginning- vs. End-of-Life (BOL vs EOL) tolerance impacts, and what circuit characteristics often fail stress and WCCA.

**NEW!**
**How WCCA Saves Money: The Case for Worst Case**

Learn about the different ways in which worst case analysis saves money, board spins, and schedule and supports continuous process improvement.

**NEW!** **Introduction to Worst Case Circuit Analysis**

Learn about skills and resources you need in order to be able to perform a worst case circuit analysis (WCCA) with this introductory presentation including detailed notes.

Taken from various lectures and AEi Systems' own WCCA Training Workshop this PowerPoint
Notes presentation discusses What WCCA is, Why and When to perform this critical
analysis, Who should perform it, and What aspects drive the cost and schedule. Common
issues found in WCCA are summarized and recommendations are made on how to improve
the efficiency of the analysis effort. Finally, the new Aerospace TOR on WCCA is
discussed by one of its authors, Charles Hymowitz (SME), along with its ramifications
and future challenges.

**Automotive WCCA
Example Report - Simulating Stability and EMC/ESD Transients for Automotive Power Supplies**

Performing WCCA for Automotive applications is not a trivial undertaking. Most SEVERELY UNDERESTIMATE the number of hours and resulting cost it takes to perform a WCCA for
the functional blocks connected to the battery. It’s easily in the hundreds of hours, even for simple circuitry. This example shows why.

**Lessons Learned from WCCA**

We know that “Worst Case Happens Everyday” and we review a lot of WCCA performed
by other companies. The quality of that work, as well as a desire to see the level
of analysis improved, motivated us to write this paper. This presentation looks
at two aspects; Lessons Learned from HOW we do WCCA and Lessons Learned from actually
DOING WCCA.

**Tailoring TOR for Class D, Commercial Space, and Cubesat Missions**

Presentation given by Charles Hymowitz at the NASA NEPP Workshop on 9.11.14. Discusses
the reasons for performing Worst Case Analysis, the issues the Testing as a substitute
for WCCA and the application of TOR-2012(8960)-4, REV. A Electrical Design Worst-Case
Circuit Analysis: Guidelines and Draft Standard principles to lower class and tech
demo/cubesat missions.

**Why Regulators Need Modeling, Testing, and Analysis**

The stability of regulator control loops and their noise performance are key factors in achieving a high level of power integrity for
downstream circuits. Designers often take their simplicity, as a sign of robustness. By way of several examples, this presentation
discusses the complex behavior that is revealed upon deeper investigation in to the control loop response. Load current and ESR variations
and their impact on output impedance, stability and step load performance and SPICE modeling are discussed.

**NEW!** **Migrating SI to GaN**

GaN is being promoted as the next generation silicon that wins in every metric including,
size, weight, cost and efficiency. There seems to be a lot of confusion about what
it means to migrate from Si to GaN. It isn’t as simple as just swapping out the
Si MOSFETs for GaN MOSFETs, though it is simpler to migrate linear regulators to
switching regulators. Not every topology is GaN friendly and not every topology
will see a performance increase. This paper will introduce the migration of linear
and switching regulators, from Si to GaN, along with some of the challenges and
trade-offs encountered along the way.

**Design a VRM with Perfectly Flat Output Impedance in 5 Seconds or Less**

Any discussion of power integrity includes a great deal of emphasis on the concept of target impedance and flat impedance requirements. But how do we design a voltage regulator module (VRM) specifically for flat impedance? This article will address not only that specific question, but how to accomplish it in 5 seconds or less.

**The inductive nature of voltage-control loops**

What is effective inductance of a voltage reference, voltage regulator, or op-amp and why is it important. "Is there really an inductor in there?", "Where does this inductance come from?", and "Why is the inductance so load current dependent?" All of these questions are answered.

**Improving Logic Timing with Worst-Case Analysis**

Digital worst case timing analysis (WCTA) analyzes the timing of digital devices
under worst case end-of-life conditions including initial, temperature, aging
and radiation tolerances. In this article the results of worst case timing analysis
are applied in order to improve the worst case performance of the design.

**Improving Circuit Designs with Logic Compatibility Analysis**

WC Logic Compatibility analysis computes the worst case DC interface compatibility for all digital interfaces.
The goal is to demonstrate positive margins for the required input voltages, positive margins for the worst case
load currents seen by the drivers, and margins for the recommended fan-out . In this article, the results of a
design analyzed using AEi Systems’ automated Logic Command software are presented.

**How do I pick the best voltage regulator for my circuit?**

There are so many different voltage regulators on the market these days.

**Simple Method to Determine ESR Requirement**

A single, simple measurement is described that allows the determination of the ESR
required to achieve a desired phase margin, using a particular value of output capacitor.
Solving the ESR requirement at the lowest operating current provides a stable solution
for higher operating currents as well.

**Component Aging in Power Converters**

Extreme environments such as oil drilling, deep sea exploration, and space applications
present daunting power supply design challenges. Power converters used in these
applications, especially in "down-hole" drilling, may be subject to temperatures
in excess of 200°C, while also facing extreme pressure.

**Unpredictable Aging Can Send Resistor Accuracy Way Off Course**

High-reliability thick-film and thin-film resistors such as those qualified to MIL-PRF-55342
promise good performance for space applications at prices that are considerably
lower than other resistor technologies like bulk foil.

**NEW!** **Designing Power for Sensitive Circuits**

The current focus on power integrity is related to maintaining a low and flat impedance
at high-speed devices such as memory devices, FPGAs, CPUs, and SerDes transceivers.
The singular goal is to ensure a stable supply voltage, within the specified range,
to these high-speed devices as their load currents are dynamically changing. This
article discusses Sensitivity to Power Supply Noise, Defining Sensitivity, Defining
Power Supply Noise Limits, Designing a Power Supply Noise Filter and High-Accuracy
Low-Noise Regulators.

**Generating Stable Voltages For Multiple
Applications**

Understanding the key parameters of diodes and other components used in reference
voltage circuits can help avoid issues in different application circuits across
many disciplines.

**Simulating RF Tuned Stages**

The ADS suite of CAE software can be used to perform simulations on RF and microwave
circuits with results that include the effects of component tuning. Assessing post-production-
tuning (PPT) elements should be part of any RF worst case circuit analysis (WCCA).

**Study of Aging Tolerance for Thin Film & Thick Film Resistors**

This paper covers the computation of resistor aging using Arrhenius models.

**So What Is Capacitor Corona?**

How Capacitor Corona can bring down your system.

**Quantifying Harmonic Distortion**

A detailed analysis of the total harmonic distortion for a non-isolated boost topology
with average current-mode control using the UC1854A and the UCC3817.

**Simulating Adaptive On-Time Switching Regulators...**

The advantages of constant on-time control in switching regulators are well understood.
However, a principal drawback is that the switching frequency can vary with input
and output voltages and the load making the EMI signature less than deterministic.

**UC1846 Gate Drive Circuit and Voltage Doublers**

This application note discusses the Texas Instruments UC1846 Current Mode PWM Controller,
MOSFET gate drive circuit simulations, and voltage doubling circuits. A full transient
model for the UC1846 is simulated.

**No-Load Specification Impacts Power-Supply Performance**

When reviewing power-supply specification requirements and supporting design proposals,
we often see the minimum load identified as 0A loading. Although not an issue in
and of itself, this no-load requirement significantly degrades the power supply's
performance.

**Gate Drive May Be the Culprit When "Q" is
Low**

The process of correlating SPICE models to bench data often leads to discoveries
of second-order and sometimes third-order parasitic elements that significantly
impact circuit performance. A couple of these side effects — a reduced circuit "Q"
and a circuit Q that is dependent on an IC's input power-supply voltage and output
circuit loading — seem to be relatively common, or at least prevalent in several
recently modeled ICs.

**Capacitor Values Don't Believe the Label**

Variations in capacitor characteristics due to DC bias and other effects impact
power-supply design and simulation, and their impact becomes greater as designers
pursue higher performance and higher reliability.

**Gain Equalization Improves Flyback Performance**

In a discontinuous flyback converter, the gain of the output current is a function
of the control voltage. A constant gain can be provided by compensating circuitry,
which improves control-loop stability.

**Optimizing Single-Stage Power Factor Correction**

A comparison of four distinct PFC topologies reveals their inherent design tradeoffs.
Based on these comparisons, a two-phase voltage mode Flyback converter is simulated
in PSpice and prototyped.

**SPICE uncovers regulator-stability problems**

An adjustable linear regulator, the LM317 is one of those products that seems to
have been around forever. Most people assume the device works just fine, but they've
got problems they weren't even aware of. In particular, its stability isn't rock
solid.

**Analyze regulator stability**

This article continues the LM317 discussion by examining how to simulate, predict
and optimize stability.

**LM317 Three Terminal Regulators Still Misunderstood**

Technology in power electronics continues to move forward at a rapid pace. Monolithic
switching regulators now offer switching frequencies above 2 MHz, synchronous rectification
available on a chip, high quality switched cap regulators and multiphase controllers
at our disposal. So why is it that we still seem to misunderstand the application
of simple three terminal regulators?

**Back to the Future with Magnetic Modulation**

More than two decades ago, I was responsible for developing the two ac-dc power
supplies that would ultimately be used in the AN/ALQ-184 Radar Jammer Pod aboard
the F-16 fighter plane. Though the application seems somewhat exotic, many of the
design goals would be considered mainstream today. What's more, some of the control
concepts used to build these supplies bear surprising resemblances to those now
being used in advanced dc-dc converters.

**A Comparison of Tolerance Analysis Methods**

We have seen many methods of calculating the worst case tolerance limits for electronic
circuits. The intent of this paper is to demonstrate several different methods and
determine the results and the corresponding confidence factors for each method.

**Failure Mechanisms Of Power Systems...**

Many challenges must be overcome when designing power systems for use in particle
accelerator-based projects. To succeed, a detailed understanding of the environment,
the potential component and functional failure modes, and the performance degradation
of the components is mandatory. This paper presents some of these challenges and
also recounts the success of such a power supply project.

**Critical Conduction and Boost Mode Power
Factor Corrector**

This article discusses two of the many transient IC models in the new Power IC Model
Library for PSpice: the MC33262 active power factor controller from ON Semiconductor
and the UC3854 high power factor preregulator from Texas Instruments.