One of the first major challenges in life is learning to write, which cannot be achieved until we learn to stay within the lines or boundaries. A major challenge in becoming a good PCB designer is to master power integrity basics, which involves learning to design a power delivery network that delivers electrical energy where it is needed within established boundaries on and from your circuit board. Not enough power can mean no functionality, and supplying too much can result in damage to components, the board, or even be harmful to persons nearby.
Power Integrity Basics: The Essentials
With the current reliance on smart devices and electronics-driven systems, it is probably safe to say that power, which all of these products rely on, makes the world go around. For electronic circuit boards, it is important that all devices are supplied with the required level of electrical energy consistently. The quality at which this goal is achieved is known as the power integrity (PI) of the PCB. Irrespective of design, there are basic power integrity elements, as described below, that are essential to your power integrity design strategy.
| ESSENTIAL POWER INTEGRITY BASIC ATTRIBUTES | ||
| Elements | Description | Why it’s important |
| Defined PI requirements | The voltage/current values required by all supplied devices. | These determine PDN requirements and establish minimums and maximums for voltages and currents. |
| Consistent Power Distribution Network (PDN) | The system of components and trace routes that distributes electrical energy to all loads. | The PDN controls and manages voltage and current levels to ensure these levels are within acceptable and safe ranges. |
| PCB Layout that follows best practices | The placement of components, traces, layers, and vias that adheres to industry standards and contract manufacturer (CM) DFMA guidelines. | Failing to adhere to industry standards; such as creepage and clearance distances, and following your CM’s DFM and DFA rules and guidelines may result in costly and time-consuming redesign and respins, or failures once installed. |
| Validation plan | A practical strategy for simulating and verifying PDN operation during design. | Performing simulations like thermal design analysis provide insight into problem areas and afford you the opportunity to correct issues that could cause damage or pose safety hazards. |
The elements listed above are essential to designing for power integrity. However, achieving a high-quality PI-designed board necessitates that certain considerations, often specific to your design objectives, are adequately addressed. How to achieve this is described for these critical power integrity basic elements below.
Power Integrity Design Requirements
PI design requirements vary based on board type. For example, specifics, including recommended decoupling capacitor parameters, differ for different speed PCBs, as listed below.
| GENERAL POWER INTEGRITY BASIC DESIGN ATTRIBUTES | ||||
| Design Element | Low-Speed (<100MHz) | Mid-Speed (100MHz-1GHz) | High-Speed (>1GHz) | Critical Considerations |
| Decoupling Capacitors | 0.1μF ceramic every 2-3 ICs | 0.1μF + 0.01μF per IC | Multiple values, <5mm from pins | ESR, ESL, resonant frequency |
| Power Plane Impedance | <1Ω target | <0.5Ω target | <0.1Ω target | Measured at switching frequency |
| Via Inductance | Standard vias acceptable | Short, wide vias preferred | Multiple vias per connection | <1nH per via typical |
| Plane Spacing | 10-20 mils typical | 5-10 mils preferred | 3-5 mils optimal | Dielectric constant impact |
| Thermal Management | Basic copper pour | Strategic thermal vias | Dedicated thermal planes | Power density >2W/in² |
The specifications above are not all-inclusive. For example, digital power consumption is often overlooked when defining PI requirements. Yet the list does provide elements that are typically important to consider for any PI strategy and PDN design.
Power Distribution Network Architecture
Your PDN serves as the foundation for reliable power integrity performance. A well-designed PDN maintains stable voltages and/or currents across all frequency ranges while minimizing impedance from DC to the highest switching frequencies in your design. The target impedance for your PDN depends on your IC specifications and switching characteristics.
An important parameter that affects the quality of power supplied to loads is ripple, which is typically caused by diode or transistor switching of converter circuitry. It is important to minimize this signal variation as much as possible. Acceptable levels can be as low as 1%. Tips for a good PDN design are:
General PDN Design Checklist:
- Calculate impedance requirements for each power rail
- Identify frequency ranges requiring different decoupling solutions
- Plan power entry points and distribution paths
- Consider voltage regulator placement and bypass capacitor requirements
PCB Layout Best Practices for Power Integrity
The PCB layout is the most difficult and time-consuming aspect of the circuit board design process. Consequently, it is important to employ methods to improve efficiency. Nevertheless, it is critical that your board layout adheres to industry and DFMA standards to ensure your design is manufacturable. Satisfying these, which may seem to be competing goals, requires implementing best practices that are required to achieve a high-quality PI design.
Proper layout techniques ensure your carefully planned PDN performs as intended in the final design. Power plane design, via placement, and thermal considerations all contribute to overall power integrity performance. Techniques for optimizing these PDN aspects are:
PCB Layout PI Optimization Techniques:
- Power plane continuity: Eliminate unnecessary splits and maintain solid reference planes
- Via placement: Use multiple vias for power connections to reduce inductance
- Thermal relief: Balance electrical connection with thermal management requirements
- Component orientation: Align decoupling capacitors for optimal current flow paths
- Decoupling: Choose capacitors based on board speed
For grounding, avoid creating plane splits that force return currents through narrow channels or alternate paths. Maintain solid reference planes under high-speed signals and provide multiple connection points between power islands to minimize impedance discontinuities.
Validating the PI of Your PCB Design
Verification of power integrity performance requires both simulation and measurement to ensure your design meets specifications across all operating conditions. Targeted impedance measurements, noise analysis, and thermal verification provide a comprehensive assessment of PDN performance. The effectiveness of your PI validation plan depends on the capabilities of the simulation tools employed. Typically, your plan should include simulation software that performs the following evaluations.
Recommended Power Integrity Simulation Capabilities
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Understanding power integrity basics is essential to creating a power integrity design that addresses your performance objectives. Achieving this mandate requires implementing simulation and analysis tools to ensure these objectives are met within the boundaries of standards and guidelines necessary for manufacturability and safe operation. Making the best choice of tools for you can be daunting. The best option may be to rely on the industry leader in helping engineers acquire the right tools and learn to use them effectively.
EMA Design Automation is a leading provider of the resources that engineers rely on to accelerate innovation. We provide solutions that include PCB design and analysis packages, custom integration software, engineering expertise, and a comprehensive academy of learning and training materials, which enable you to create more efficiently. For more information on essential power integrity basics for your design and how we can help you or your team innovate faster, contact us.
